Putting all the McClellan stuff in one place...

Saphroneth

Major
Joined
Feb 18, 2017
It sounds like there was some kind of organizational SNAFU, then, about whether Porter was allowed to take his whole corps.

I see from the correspondences in the ORs that Porter was ordering Whipple to send Tyler and Allabach to concentrate as a division under Humphreys on the 11th, but there doesn't seem to be a reason for him to do that if he was to take his whole corps and that included Whipple etc. (As Porter tells Whipple "you remain as essential to the defences on this side", so he's not just leaving Whipple with no troops).


Porter's statement about being offered a division en route through Washington may be a case of misremembering, or it may be a gloss on something else that's going on (such as Porter being told that anything he doesn't take with him won't be part of 5th Corps any more). Certainly Whipple's division is not considered part of 5th Corps on the 20th, so perhaps it was an ad-hoc thing.


This would then imply:

In addition to Morell's division (which based on the September 2 state, casualties from the 2BR campaign and the August 10 state was probably not more than 7,000 PFD after the addition of two extra regiments), Porter was on the 10th in command of additional troops south of the Potomac (including but not limited to what would become Humphreys' division, that being about 6,800 PFD) which brought his strength up to 21,000 to 23,000 men PFD. These men may have been formally assigned to 5th Corps, or they may have simply been in "Porter's sector" and thus informally under Porter's command.

If that 21,000 to 23,000 men PFD total included Sykes, then the additional troops not factored into that would number just 1,700 to 3,700 PFD, which would match with the strength of "Whipple" on the September 20 report.

If however that was the case, then the reduction in strength of Whipple's command in AP&A would reflect the departure of Tyler and Allabach, and the reduction is not large enough to reflect this. This is a bit of a mystery.

The Aggregate Present and Absent listed for Morell's division in the September 20 report from Banks (17,000) does not just reflect Morell's division - a mathematical impossibility as far as I can tell - but may also reflect some or all of Humphreys' division.

The AP&A of 5th Corps in the Army of the Potomac report is 32,679, which is an increase of about 2,000 from the same number on August 10; in that time the PA Reserves at 10,700 AP&A have been assigned away and casualties have been suffered but Morell gained two new regiments and Humphreys is eight entirely new/green regiments. The numbers don't seem to quite add up.
 

NedBaldwin

Major
Joined
Feb 19, 2011
Location
California
I dont see any SNAFU. Porter was ordered to take Morrell and two brigades from Whipple formed into a new division and so he did. The last brigade of Whipple was detached from the 5th Corps and remained in the defenses.

I dont have time right now to go through all your numbers but I think Morell added more than 2 regiments

Do you have any order for a so called "Porter's sector" than included troops not part of his Corps? Otherwise this idea that Porter's command extended beyond his corps seems unsupported

It sounds like there was some kind of organizational SNAFU, then, about whether Porter was allowed to take his whole corps.

I see from the correspondences in the ORs that Porter was ordering Whipple to send Tyler and Allabach to concentrate as a division under Humphreys on the 11th, but there doesn't seem to be a reason for him to do that if he was to take his whole corps and that included Whipple etc. (As Porter tells Whipple "you remain as essential to the defences on this side", so he's not just leaving Whipple with no troops).


Porter's statement about being offered a division en route through Washington may be a case of misremembering, or it may be a gloss on something else that's going on (such as Porter being told that anything he doesn't take with him won't be part of 5th Corps any more). Certainly Whipple's division is not considered part of 5th Corps on the 20th, so perhaps it was an ad-hoc thing.


This would then imply:

In addition to Morell's division (which based on the September 2 state, casualties from the 2BR campaign and the August 10 state was probably not more than 7,000 PFD after the addition of two extra regiments), Porter was on the 10th in command of additional troops south of the Potomac (including but not limited to what would become Humphreys' division, that being about 6,800 PFD) which brought his strength up to 21,000 to 23,000 men PFD. These men may have been formally assigned to 5th Corps, or they may have simply been in "Porter's sector" and thus informally under Porter's command.

If that 21,000 to 23,000 men PFD total included Sykes, then the additional troops not factored into that would number just 1,700 to 3,700 PFD, which would match with the strength of "Whipple" on the September 20 report.

If however that was the case, then the reduction in strength of Whipple's command in AP&A would reflect the departure of Tyler and Allabach, and the reduction is not large enough to reflect this. This is a bit of a mystery.

The Aggregate Present and Absent listed for Morell's division in the September 20 report from Banks (17,000) does not just reflect Morell's division - a mathematical impossibility as far as I can tell - but may also reflect some or all of Humphreys' division.

The AP&A of 5th Corps in the Army of the Potomac report is 32,679, which is an increase of about 2,000 from the same number on August 10; in that time the PA Reserves at 10,700 AP&A have been assigned away and casualties have been suffered but Morell gained two new regiments and Humphreys is eight entirely new/green regiments. The numbers don't seem to quite add up.
 

Saphroneth

Major
Joined
Feb 18, 2017
I dont see any SNAFU. Porter was ordered to take Morrell and two brigades from Whipple formed into a new division and so he did. The last brigade of Whipple was detached from the 5th Corps and remained in the defenses.

I dont have time right now to go through all your numbers but I think Morell added more than 2 regiments

Do you have any order for a so called "Porter's sector" than included troops not part of his Corps? Otherwise this idea that Porter's command extended beyond his corps seems unsupported
I haven't been able to locate the order where Porter was ordered to take "Morell and two brigades from Whipple" - I've found mention of Porter's entire force being ordered, but no more than that, and if Porter's entire force was Morell + 3 bdes Whipple then the numbers don't line up - you need Sykes as well, but in that case saying Porter was taking 21,000 troops to join McClellan is double counting Sykes at least, plus erroneously counting the third brigade of Whipple.


My reasoning for the "Porter's sector" is precisely that it would be a way for there to be troops who were under Porter's command but not assigned to his corps, as an ad-hoc result of the complicated situation going on. I'm not saying it's necessarily the case, and if there's orders which state that Whipple's last brigade was formally detached from 5th Corps then that is a good bit of evidence that it's not.


As for Morell adding more than two regiments, Morell's composition was:

Seven Days​
By twentieth July and through Northern Virginia​
Maryland Campaign​
Division​
Brigade​
Regiment​
Regiment​
Regiment​
Morell​
1st​
2nd Maine​
2nd Maine​
2nd Maine​
Morell​
1st​
18th Mass​
18th Mass​
18th Mass​
Morell​
1st​
22nd Mass​
22nd Mass​
22nd Mass​
Morell​
1st​
1st Mich​
1st Mich​
1st Mich​
Morell​
1st​
13th NY​
13th NY​
13th NY​
Morell​
1st​
25th NY​
25th NY​
25th NY​
Morell​
1st​
32nd Mass
32nd Mass joined and then left​
Morell​
1st​
20th Maine
New for Maryland​
Morell​
1st​
118th PA
New for Maryland​
Morell​
2nd​
9th Mass​
9th Mass​
9th Mass​
Morell​
2nd​
4th Mich​
4th Mich​
4th Mich​
Morell​
2nd​
14th Mich​
14th Mich​
14th Mich​
Morell​
2nd​
62nd Penn​
62nd Penn​
62nd Penn​
32nd Mass​
Transferred from 1st Bde​
Morell​
3rd​
16th Mich​
16th Mich​
16th Mich​
Morell​
3rd​
12th NY​
12th NY​
12th NY​
Morell​
3rd​
17th NY​
17th NY​
17th NY​
Morell​
3rd​
44th NY​
44th NY​
44th NY​
Morell​
3rd​
83rd PA​
83rd PA​
83rd PA​
Other​
1st US Sharpshooters​
1st US Sharpshooters​
1st US Sharpshooters​

So yes, only two regiments joined between 20 July and 20 September. Porter's -> Morell's division was already one of the strongest by regiment count, which is why it has so many regiments, but the increase was only by two regiments.
 

NedBaldwin

Major
Joined
Feb 19, 2011
Location
California
I haven't been able to locate the order where Porter was ordered to take "Morell and two brigades from Whipple" - I've found mention of Porter's entire force being ordered, but no more than that, and if Porter's entire force was Morell + 3 bdes Whipple then the numbers don't line up - you need Sykes as well, but in that case saying Porter was taking 21,000 troops to join McClellan is double counting Sykes at least, plus erroneously counting the third brigade of Whipple.


My reasoning for the "Porter's sector" is precisely that it would be a way for there to be troops who were under Porter's command but not assigned to his corps, as an ad-hoc result of the complicated situation going on. I'm not saying it's necessarily the case, and if there's orders which state that Whipple's last brigade was formally detached from 5th Corps then that is a good bit of evidence that it's not.


As for Morell adding more than two regiments, Morell's composition was:

Seven Days​
By twentieth July and through Northern Virginia​
Maryland Campaign​
Division​
Brigade​
Regiment​
Regiment​
Regiment​
Morell​
1st​
2nd Maine​
2nd Maine​
2nd Maine​
Morell​
1st​
18th Mass​
18th Mass​
18th Mass​
Morell​
1st​
22nd Mass​
22nd Mass​
22nd Mass​
Morell​
1st​
1st Mich​
1st Mich​
1st Mich​
Morell​
1st​
13th NY​
13th NY​
13th NY​
Morell​
1st​
25th NY​
25th NY​
25th NY​
Morell​
1st​
32nd Mass
32nd Mass joined and then left​
Morell​
1st​
20th Maine
New for Maryland​
Morell​
1st​
118th PA
New for Maryland​
Morell​
2nd​
9th Mass​
9th Mass​
9th Mass​
Morell​
2nd​
4th Mich​
4th Mich​
4th Mich​
Morell​
2nd​
14th Mich​
14th Mich​
14th Mich​
Morell​
2nd​
62nd Penn​
62nd Penn​
62nd Penn​
32nd Mass​
Transferred from 1st Bde​
Morell​
3rd​
16th Mich​
16th Mich​
16th Mich​
Morell​
3rd​
12th NY​
12th NY​
12th NY​
Morell​
3rd​
17th NY​
17th NY​
17th NY​
Morell​
3rd​
44th NY​
44th NY​
44th NY​
Morell​
3rd​
83rd PA​
83rd PA​
83rd PA​
Other​
1st US Sharpshooters​
1st US Sharpshooters​
1st US Sharpshooters​

So yes, only two regiments joined between 20 July and 20 September. Porter's -> Morell's division was already one of the strongest by regiment count, which is why it has so many regiments, but the increase was only by two regiments.
You show 3 regiments -- 32nd MA, 20 ME and 118 PA -- and you are missing the 2nd DC.
 

Saphroneth

Major
Joined
Feb 18, 2017
You show 3 regiments -- 32nd MA, 20 ME and 118 PA -- and you are missing the 2nd DC.
32nd MA joined before July 20 (specifically they joined around July 3 at Harrisons Landing), so they're not relevant to changes from the July 20 strength. Look at 1st Brigade.

The 2nd DC is a regiment I indeed missed, thanks for pointing it out (the error here is that the site I was using missed it). That means the increase was three regiments, rather than two.
 

wausaubob

Lt. Colonel
Joined
Apr 4, 2017
Location
Denver, CO
years ago I spent a good deal of time studying the interaction between Pope Halleck and McClellan at the end of August and came to the conclusion that Halleck was the one that screwed everything up. Halleck had given Pope the impression that Halleck had assigned some force from DC to guard Manassas so Pope felt he was secure from the kind of move Jackson did; but this wasnt the case. And McClellan acted as best he could given what Halleck was telling him, but Halleck's directions were fluctuating and unclear. Halleck also bears responsibility for pulling McClellan from the peninsula while pushing Pope further from DC. So in general, I think putting Halleck in charge of everything was the worst thing to happen in August 1862. He also left things in the west ambiguous and open to command confusion.
McClellan's biggest problem was Halleck. Halleck did not want McClellan to get south of the James, just like he ridiculed Grant's operation to extend westward south of the James and Appomattox. Halleck did not have to do anything about Buell. Don Carlos Buell was capable of self destruction.
Halleck wanted to be the general that won the US Civil War.
It took Lincoln and Stanton about 16 months to figure out that Halleck's intellectualism did not correspond to any understanding of conditions in the US and Confederacy.
 

NedBaldwin

Major
Joined
Feb 19, 2011
Location
California
I haven't been able to locate the order where Porter was ordered to take "Morell and two brigades from Whipple" - I've found mention of Porter's entire force being ordered, but no more than that, and if Porter's entire force was Morell + 3 bdes Whipple then the numbers don't line up - you need Sykes as well, but in that case saying Porter was taking 21,000 troops to join McClellan is double counting Sykes at least, plus erroneously counting the third brigade of Whipple.
Porter to Whipple on September 11 -- telling Whipple to put Tyler and Allabach in motion and have them report to him at Brookville; Whipple to remain, Humphreys to command the new division. Porter wrote McClellan (or really Seth Williams) the next day that he was on his way with Morrell, and Tyler and Allabach under Humphreys. Halleck followed up with Heintzelman telling him to get Tyler and Allabach on the move to Porter, who had already gone ahead.



My reasoning for the "Porter's sector" is precisely that it would be a way for there to be troops who were under Porter's command but not assigned to his corps, as an ad-hoc result of the complicated situation going on. I'm not saying it's necessarily the case, and if there's orders which state that Whipple's last brigade was formally detached from 5th Corps then that is a good bit of evidence that it's not.
So you have just hypothesized it rather than shown any order for it?
 

Saphroneth

Major
Joined
Feb 18, 2017
Porter to Whipple on September 11 -- telling Whipple to put Tyler and Allabach in motion and have them report to him at Brookville; Whipple to remain, Humphreys to command the new division. Porter wrote McClellan (or really Seth Williams) the next day that he was on his way with Morrell, and Tyler and Allabach under Humphreys. Halleck followed up with Heintzelman telling him to get Tyler and Allabach on the move to Porter, who had already gone ahead.
That's not the order to Porter, though; it's the order from Porter. I already accept that one exists, but you said:

Porter was ordered to take Morrell and two brigades from Whipple formed into a new division and so he did.



So you have just hypothesized it rather than shown any order for it?
My understanding had originally resulted from Stoltemyer; what I'm trying to do is to understand why Porter left behind the third brigade of Whipple, and why it is that he later described Morell's division as "all I had the right to take".


Looking through the ORs, I note:

On September 6th Porter sent
1616688563032.png


This means that his command at the time, or the force he was responsible for, included Piatt's brigade. On the 2nd September this was part of the Reserve Corps (not the 5th Corps), though was under Porter at the time.
There is thus a precedent for the idea of a force being under Porter but not part of 5th Corps.


Special Order 3 gives:

1616688976825.png


Now, clearly not all of these assignments actually meant that the regiment was assigned to that formal corps. We just need to look at the regiments assigned to Franklin's Corps in this order to see that - 18th Maine, 19th Maine, 136th Pennsylvania, 137th Pennsylvania. Of those:

18th Maine went to the defences of Washington and stayed there, eventually being converted to Heavy Artillery.
19th Maine stayed in the defences of Washington, and joined the 2nd Corps in October.
136th Pennsylvania stayed in the defences of Washington, and joined 1st Corps at the end of September.
137th Pennsylvania did indeed join 6th Corps and was at Antietam.

In addition the 121st PA was at Arlington Heights and did not march with 6th Corps.

Which seems to me to further suggest that it's possible for units to "join Franklin's Corps" without actually joining, well, 6th Corps.
 

Saphroneth

Major
Joined
Feb 18, 2017
Measuring Lee's army in Maryland


There are these ways in which we can measure the strength of Lee's army.


What Steiner Saw


Other observations


Taking the September 2 strength and go forwards from there


Taking the October 10 report (the first complete report, which includes the cavalry) and adding back either admitted Confederate casualties, total derived casualties (based on burials, captures and known wounded) or a casualty count based on the second but reduced according to how many were still sick


Taking the September 22 report (which is noted as "very imperfect") and adding back casualties (either admitted or derived), for an estimate of troops with their units on the field


Taking Carman's strengths on the field (at Antietam) and going through carefully to tease out errors


Generalized company/regiment count


Officer count by analogy with non-new regiments from McClellan's force



Not all of these strength measures will generate the same number, and some will or will not account for straggling. The September 2 report (the Schulte ORBAT) is in Effectives, and the same or similar is true for the September 22 and October 10 reports (which are in Confederate PFD).

Method​
What does it show​
What should we compare it with​
Steiner’s observation​
Size of the moving armed bodies, not counting wagons​
Not immediately clear – Union PFD or Union AP​
Other observations​
Size of the moving armed bodies​
Probably Union PFD or AP, depending on if wagons are included​
September 2 strength​
Confederate Effectives before straggling​
Union effectives calculated as 0.8 of PFD (known calculation)​
October 10 strength and add-back​
Confederate PFD for the campaign​
Union PFD with casualties added back, with caveats​
September 22 report and add-back​
Confederate strength on the field (plus Thomas’ brigade)​
Union PFD on the field, from McClellan’s report, though with caveats​
Carman’s strength​
Effectives on the field at Antietam​
Carman’s strength for the Union​
Regiments of all arms​
Estimated strength based on ROAA​
Union ROAA count (green regiments are stronger numerically but not necessarily in combat terms, and heavily depleted Union regiments partly compensate)​
Officer count​
Strength in any given category​
Union strength in the appropriate category (i.e. compare officer strengths)​



What Steiner saw:

Steiner saw the main body of the Confederate force (Jackson's corps, Longstreet's corps, McLaws, Anderson, and the reserve artillery) to be "not more than 64,000".
This is:
557 companies in Longstreet's command
141 companies in Anderson's division
683 companies in Jackson's command
164 companies in McLaws' command
19 companies in Pendleton's reserve artillery
1,564 total

And implies 40.9 men per company in this category.

He also saw DH Hill's division (minus GB Anderson) to be 8,000. This is 193 companies, and implies 41.5 men per company in this category.



The other observations have been compiled by Gene Thorp for an article in the Washington Post, and they are:

Observation​
Number​
Companies​
Men per coy​
Whole army, September 4-6, said by a Virginia captain in Leesburg​
84000​
2015​
41.7​
Whole army, September 8​
75000​
2015​
37.2​
Whole army, September 9, Rebel deserter​
100000​
2015​
49.6​
Whole army, September 9, telegraph operator, over 100,000​
100000​
2015​
49.6​
Whole army, September 10, newspaper, 60,000 to 100,000​
80000​
2015​
39.7​
Main Body (Jackson Longstreet McLaws Anderson res art), September 10​
60000​
1564​
38.4​
Main Body (Jackson Longstreet McLaws Anderson res art), September 10​
70000​
1564​
44.8​
Main Body (Jackson Longstreet McLaws Anderson), September 10, “40,000 to 60,000”​
50000​
1564​
32.0​
Walker​
6000​
92​
65.2​
Jackson, Williamsport, “15,000 men and 70 pieces of artillery”​
15000​
683​
22.0​
Jackson, south of Williamsport, “not less than 25,000”​
25000​
683​
36.6​
Jackson, 6 miles west of Williamsport, “15,000 infantry, 100 cavalry, 40 pieces of artillery”​
15000​
683​
22.0​
Jackson, west of Martinsburg, “with a force of 20,000”​
20000​
683​
29.3​
McLaws and Anderson, “30,000 men at Burkittsville”​
30000​
305​
98.4​
McLaws and Anderson, “25,000 down to 12,000”​
18500​
305​
60.7​
Anderson, “8,000 or 10,000 of the enemy”​
9000​
141​
63.8​
McLaws and Anderson, “some 30,000 of the enemy’s troops on the heights”​
30000​
305​
98.4​
McLaws or McLaws and Anderson, “I thought there were some 12,000 or 15,000, perhaps more”​
13500​
305​
44.3​
Longstreet’s Command, “20,000 to 30,000”​
25000​
557​
44.9​
McLaws and Anderson passing over from Maryland Heights, counter gave up after counting 17,600 infantry in 22 regiments averaging about 800​
17600​
305​
57.7​
McLaws and Anderson passing over from Maryland Heights, “20,000, perhaps 30,000”​
25000​
305​
82.0​
Total attacking force at Harpers Ferry (Jackson, McLaws, Anderson, Walker) “amounting in all to 40,000”​
40000​
1080​
37.0​



September 2 strength


The Schulte ORBAT has the total strength of the Army of Northern Virginia on September 2 as 75,687 men (in effectives), which equates to a little over 94,000 Union PFD given the conversion factor Schulte used when generating Union strength for this report.


In major formations:
Unit Name
Strength
Cos.
Effectives per coy​
PFD per coy​
Confederate Army: September 2, 1862
Army of Northern Virginia / General Robert E. Lee
75687
2015
37.6​
47.0​
Longstreet's Command / MG James Longstreet
19624
557
35.2​
44.0​
Jones' Division / BG D.R. Jones
3724
126
29.6​
36.9​
Wilcox's Division / BG Cadmus Wilcox
5582
130
42.9​
53.7​
Kemper's Division / BG James L. Kemper
4887
152
32.2​
40.2​
Hood's Division / BG John B. Hood
3839
92
41.7​
52.2​
Evans' Independent Brigade / BG N.G. Evans
996
49
20.3​
25.4​
Longstreet's Artillery Reserve
590
8
73.8​
92.2​
Anderson's Division / MG R.H. Anderson
5712
141
40.5​
50.6​
Jackson's Command / MG Thomas J. "Stonewall" Jackson
20608
683
30.2​
37.7​
Jackson's Division / BG W.E. Starke
5646
198
28.5​
35.6​
Ewell's Division / BG A.R. Lawton
6383
218
29.3​
36.6​
A.P. Hill's "Light" Division / MG A.P. Hill
8570
267
32.1​
40.1​
Cavalry Division / MG J.E.B. Stuart
5664
127
44.6​
55.7​
Reinforcing Column
24071
507
47.5​
59.3​
McLaws' Division / MG Lafayette McLaws
7765
164
47.3​
59.2​
D.H. Hill's Division / MG D.H. Hill
9848
232
42.4​
53.1​
Walker's Division / BG John G. Walker
5159
92
56.1​
70.1​
Reserve Artillery / BG W.N. Pendleton
1299
19
68.4​
85.5​


McClellan's force marching out of Washington (discounting cavalry) was on the order of 178 regiments (1,780 companies) and was on the order of 75,000 PFD, which gives about 42 men per company. This is on par with Longstreet's force, less than the Confederate reinforcing column and more than Jackson's hard-fought formation, which is a good sign for this calculation being reasonable. The accession of reinforcement regiments over the course of the campaign would tend to drive up the average per-company strength (though he did not join, Humphreys for example was about 6,800 in 82 companies and would thus be an average of 83 men per company organization) towards parity with Lee's total.

I should also point out that the Confederate batteries are often quite strong, though I've counted them as one company each. This may be the result of them just not being in the forefront of the fighting much - no battle yet had had the Confederate artillery line "overrun", especially not the reserve artillery which is broken out separately here. At Second Bull Run meanwhile many Union batteries lost all their guns.



To add back casualties, we need to know how many casualties were suffered in the campaign as a whole (this will generate numbers which are whole-campaign, not Antietam).


We have the following known information:

McClellan's medical director, Letterman, reported 2,500 wounded Confederates under his care following the battle.
OR S1 V19 P1 Pg 111:
"In addition to our own wounded, we had upon our hands from the battles of South Mountain, Crampton's Gap, and Antietam in all about 2,500 Confederate wounded".
At about the same time, about 3,000 unwounded prisoners were held in Fort Delaware (of which 3/4 were exchanged) and a minimum of 224 were in Fort McHenry (that's the number exchanged from there).
In the cemeteries associated with Antietam there are 3,270 Confederate graves, of which 690 were buried in Shepherdstown and Winchester (and thus were buried by the Confederates) and the rest of which were buried or reburied by the Union:
The Confederates who were captured mortally wounded and subsequently perished in Union hospitals were buried at Mount Olivet, and numbered 112.
The Confederates reinterred at Washington Confederate Ceremony years after being buried on the battlefield numbered 2,468.
The number of Confederates who were mortally wounded and died at Shepherdstown numbered 114 (and were buried at Elmwood).
The number who died at the hospitals in Winchester and were buried there is 576.

There are a number of disconnected reports which give Confederate casualties. One report gives the casualties in troops under Longstreet's command as 964 KIA, 5,236 WIA and 1,310 MIA.
Another for Hood's division alone gives casualties from Northern Virginia and Maryland campaigns mostly intermingled, and if the Maryland campaign casualties alone are used gives 122 KIA, 807 WIA and 87 MIA.

The most complete single report is Lafayette Guild's report of killed and wounded at South Mountain, Crampton's Gap, Harper's Ferry, Antietam and Shepherdstown. This report however misses out some regiments and even entire brigades (such as the cavalry and the reserve artillery).
It gives as the total 1,567 killed and 8,724 wounded. The shortcomings of this report are:
AP Hill's division is listed en masse rather than broken out into regiments.
Rodes' brigade is listed en masse.
Jones' brigade (3 regiments, 1 battalion) is not listed.
The following regiments are not listed:
4th SC Bn
3rd SC Bn
Philips' Legion
9th VA
5th FL
61st VA
10th VA
1st Louisiana Zouaves
26th GA
38th GA
58th VA
14th LA
21st GA
21st NC
1st NC Sharpshooters
5th NC
12th NC
13th AL

In addition some batteries are not listed (though it is possible they took no casualties) and the cavalry, as mentioned, is unlisted.
All told this means that Guild's report misses more than 10% of the Confederate infantry formations and all the cavalry.

Totalling the more granular individual reports (as done by Gene Thorp, looking at OR Vol. 27, pages, 843, 861, 862, 888, 925, 974, 975, 983 and 1026) comes to a total of 1,674 killed, 9,451 wounded and 2,292 missing for a total of 13,417. This may also be missing some casualties.

To tally this up without double counting, we would begin:

MIA
5,000 or more (as this is the number of wounded Confederates under Letterman's care, plus the number of unwounded Confederates who were held in Forts Delaware and McHenry and were subsequently exchanged. Using 5,000 excludes about 750 men who were not exchanged but for these purposes I will be doing this).
KIA
2,468 (as this is the number who were buried on the field of battle)

As of yet there is no double counting.

Moving on to Confederate reports, the only way to be certain we are avoiding double counting is to count only the total listed wounded in the Confederate reports. If the reports were compiled immediately after the army crossed the river, then using the wounded count and adding burials on the Confederate side of the river would risk double counting men who died in hospitals after the report was compiled. (Anyone who was left behind wounded would either die - and be buried on the field - or not die - and become one of the captured wounded statistics.)

This number is 9,451 wounded.

The total estimate of Confederate casualties in the Maryland Campaign thus comes to a lower bar of 16,919.


I should note here that post-war the surgeon-general assessed the Confederate casualties of the campaign as:

Harpers Ferry
500 WIA

South Mountain
500 KIA, 2343 WIA, 1500 MIA

Antietam
3500 KIA, 16399 WIA, 6000 MIA

Shepherdstown
33 KIA, 231 WIA

Total
4033 KIA, 19473 WIA, 7500 MIA


So the 16,919 number is a lower bar and the casualties could have been significantly higher, which would in turn push the estimates of things like the amount of straggling that took place lower.




Post battle reported strength and add-back

The September 22 return, the first filed after the battle, gives:
Longstreet's corps 1,574 officers and 19,001 men (total 20,575)
Jackson's corps 1,158 officers and 14,685 men (total 15,843)

These are given in PFD.

This report is noted as being "very imperfect". It does not include the cavalry or reserve artillery.

The September 30 report gives:

Longstreet's corps 2,018 officers and 26,481 men (total 28,499)
Jackson's corps 1,784 officers and 21,728 men (total 23,512)
The reserve artillery is listed as 55 officers and 716 men (total 771)
The cavalry is still not listed.
This report is also noted as being "incorrect".

The October 10 report gives:

Longstreet's corps 2,146 officers and 27,934 men (total 30,080)
Jackson's corps 1,917 officers and 25,603 men (total 27,520)
Cavalry 423 officers and 5,338 men (total 5,761)
Reserve artillery 54 officers and 858 men (total 912)

At this date Lafayette Guild reported that there were still about 5,000 sick and wounded at Winchester and that they were being moved to Staunton.

Given that the number of men who died of wounds south of the Potomac is 690, this allows us to estimate that of the 9,451 wounded we initially had on record as south of the Potomac then as of October 10:
690 died
3,761 may have returned to the ranks*
5,000 remain convalescent
* This estimate assumes that no wounded were sent to anywhere else or kept at Shepherdstown, and is therefore the largest possible estimate.


Adding back casualties in the same way that McClellan did to estimate his pre-Antietam strength, and bearing in mind that Confederate-recorded PFD may not be the same as Union-recorded PFD:


Using the September 22 report, but the 30 September number for artillery and the 10 October number for cavalry:
Longstreet 20,575
Jackson 15,843
Reserve artillery 771
Cavalry 5,761
All casualties 16,919 (this is a slight overestimate as some of the 3,761 casualties estimated to have recovered by October 10 may have been cavalry or reserve artillery)
Total estimate 59,869

This is effectively the Confederate strength in the campaign, minus stragglers (particularly stragglers south of the Potomac, such as on the marches undertaken by the commands of Jackson, McLaws, Anderson and Walker). It also includes some of the post-Antietam disruption to the Army of Northern Virginia.


Using the October 10 report, and counting 3,761 casualties as having returned to the ranks:
Longstreet's 30,080
Jackson 27,520
Cavalry 5,761
Reserve artillery 912
All casualties 16,919
-3,761 returned to the ranks
Total estimate 77,431

This is effectively an estimate of the strength with which Lee campaigned during the Maryland Campaign. It is quite close to the 75,000 figure from Allen's MA thesis (which is Effectives).




The next one on the list is Carman's strengths. This doesn't mean Carman's raw numbers, but going through to (1) identify the cases where Carman used numbers which may be or are not quite in the right category and (2) include unengaged units, which is something Carman did not do.

Doing this at Antietam for the Confederacy results in:




DH Hill: DH Hill claimed 3,000 infantry, but Carman calculated 5,449 infantry and 346 artillery.
Via Clemens we get:
Ripley's brigade: 1,349 infantry into action
Rodes' brigade: 3rd, 6th and 12th Alabama carried 840 into action, excluding at least the officers of the 12th. 5th Alabama was a small regiment, but no clue about the 26th; if the 5th and 26th average the same as the other three then it's ca. 1,400.
Colquitt's brigade, from Carman's correspondence:
6th Georgia: 300+ (and one company on picket not counted)
23rd Georgia: 485 men (not officers)
27th Georgia: 400 men (not officers)
28th Georgia: 250 men or 250-275 officers and men
13th Alabama: Carman guessed 310 based on a 2nd September strength of 612
Which implies that there were ~1,780 men plus officers, for a brigade strength of ~1,900
Garland's brigade:
Carman gives the brigade 756, but it was the strongest in the division on the 2nd September (though it did then take plenty of casualties at South Mountain) and the 5th North Carolina had ~625 men at Antietam. Adding officers and assuming the other four regiments are each about half the size of the 5th NC gives an estimate of about 2,100, but I'd say we could go with 1,700 to avoid overclaiming. Effectively this is assuming the other four regiments average 250 officers and men.

GB Anderson's brigade - Carman gives 1,174 and this seems fairly solid.
Divisional total:
1349+1400+1900+1700+1174 = 7,523 infantry, and 346 gunners.


McLaws: Carman gives 2,823 infantry and 138 gunners. This might actually make sense, on 2nd September McLaws disposed of 7,340 infantry and 419 gunners but they got hit hard at Crampton's Gap and suffered 1,907 claimed infantry casualties. If the actual casualties were higher and there was the usual straggling, or those casualties and a bit more than the usual straggling, then I suppose it's possible they could be down to about 3,000.

RH Anderson: The brigades except for Armistead (who remained in reserve) were sent to reinforce DH Hill, who estimated it at ca. 3,000-4,000. As we've seen DH Hill's estimated strength was really low for his own division, so it could be considerably higher. (The 22nd September return gives 5,324 PFD, and it suffered 1,278 casualties at Antietam; it'd probably be reasonable to say it had about 5,000 actually with the division once Armistead is counted.)

Walker: Carman calculated 3,764 infantry and 230 artillery.

DR Jones: DR Jones himself estimated "only 2,430 men" from a pre-campaign PFD of 8,953 infantry; he suffered about 1,000 casualties in the pre-Antietam fighting, but being down to less than 2,500 simply isn't credible. In particular this division includes Drayton's brigade, which is the one that had had almost no straggling until September 11th, so a lot of the hypothetical stragglers would have had to fall out of line and be swept up.
Carman estimated 3,311 infantry and 81 artillery, but going brigade by brigade:

Toombs: Toombs claimed over 400 muskets in the 2nd and 20th Georgia, while Carman estimated 357 officers and men in the same two regiments. Then 15th and 17th Georgia (Carman est. 281 muskets) joined them, and half the 11th Georgia (reported as 140 muskets in the five companies present).
This implies about 750-780 men minus officers, or a bit more with officers (so ca. 825).

Garnett: Carman gave 261 officers and men in the brigade, arguing that the brigade was recruited from near where Lee crossed the Potomac and briefly deserted. This would imply something like 80% of the brigade had either done that or was elsewhere.

Kemper: Carman estimates 443 on the field by adding regimental reports and guessing for the 28th VA, but others reported the brigade at 500-600 muskets (which would imply 600 or so with officers added, indicating the 28th VA was a strong regiment). 600 would also indicate straggling of about 50%.

GT Anderson - Carman estimates 597, but see Hood/Evans...

Drayton: Carman estimates 465, excluding 11th Georgia (detached and one wing fought in Toombs' brigade, 140 men counted there). Carman was told by a veteran the 15th SC had 300 men, but he used 200 in his calculation. Carman's estimate of 100 for the 51st Georgia is given no basis but we'll use it. The Phillips Legion infantry was also present, but Carman doesn't include it.
Correcting the 15th SC from 200 to 300, and adding the Phillip's Legion (ca. 135) plus adding officers would be ca. 700 men plus about 80 officers, so 780.

Jenkins: Carman quotes a newspaper to give 755 but in correspondence with the brigadier he's told 1,250 officers and men plus the 1st SC (106). So 1,356.

This totals to 825+261+600+780+1356 infantry, for 3,822 infantry (not including GT Anderson) plus 81 artillery.

Hood/Evans:

Carman says Evans' brigade straggled really badly, down to 284 infantry and 112 gunners for 396 all told. That's down from 1,058 on 2nd September, though there were 216 casualties so it means "only" about 53% straggling, or 47% of the strength in line.

Hood's brigade and Whiting's brigade are estimated at 2000 infantry (Hood gave this) and 304 artillery, and this does not include officers (so ca. 230 officers). 2230 infantry means about 62% of theoretical strength in line.

GT Anderson's brigade: 597, and Evans claimed it in his report. That's about 43% of theoretical strength which is another bad straggle.

Total for these four brigades considered here is 3,111 infantry and 416 artillery.

Jackson: As covered above, the number Carman gives is 1,784 infantry and 310 artillery, but this is just after the arrival on the field. If we take Starke's number of 1,400-1,500, take the low number (1,400) and correct the other three brigades to match then we multiply their September 2 strength by 0.86, to give:
Grigsby 1,000
Johnson 700
Warren 1,330
Starke 1,400
Total 4,430 infantry and 310 artillery

Ewell:
Carman gives 3,904 infantry and 223 artillery, but for once there's full reports in the OR. Ewell moved more slowly than the Stonewall division and took care to keep his straggling under control (he paused south of Boteler's Ford to collect up stragglers before crossing), and Lawton and Early's brigades match very closely to 22nd September PFD plus casualties; the other two don't.
It looks like there's an artillery battery buried in the reports for Hays and Trimble (as Ewell's division reported artillery in brigade totals) and the numbers for Hay and Trimble are also a bit vague - Hays' entire brigade is reported as the force Hays took to the wheatfield, and Trimble is just "out of less than 700 men carried into action". Assuming the four brigades behaved similarly you get about 1,000 in both (1078 instead of 550 for Hays and 1029 instead of 700 for Walker) but this includes the artillery. This would give a total of about 4,400 infantry and 223 artillery, and would mean that there were 73% of the infantry in battle - what we'd expect from a division that controlled straggling especially well.

AP Hill: Carman gives 2,231 infantry for the three engaged brigades, plus 337 artillery. The three engaged brigades were Branch, Archer and Gregg (2nd September total 3,887, so 57.3% of 2nd September strength engaged), with Pender and Field (2nd September total 2,932) not engaged; if Pender and Field straggled as much as Branch, Archer and Gregg, that gives an extra 1,683 infantry for a total of 3,914 infantry and 337 artillery on the field.
Thomas was of course not on the field.

Total strengths of the infantry divisions:

DH Hill 7523 + 346
McLaws 2823 + 138
Anderson 5,000 + 0
Walker 3,764 + 230
DR Jones 3,822 + 81
Hood/Evans 3,311 + 416
Jackson/Stonewall 4,430 + 310
Ewell 4,400 + 223
AP Hill 3,914 + 337

Total infantry 38,987

Carman gives the cavalry directly at 4,500, and the total artillery at 3,629. This would mean a grand total of

47,116 effectives




This estimate has large error bars on it, and could be off by a few thousand either way. There were also quite a lot of men who have to have been just behind the lines, as taking the September 22 return and adding back casualties gives just under 60,000 for the whole army - a difference of 13,000 men.



The comparable number for the Union is:


Infantry



1st Corps
Meade said that ca. 9,000 were carried into battle, and Carman estimated 8,619 infantry were on the field. Notably they got only 63% of their infantry PFD into the firing line as assessed at the time.


2nd Corps
Carman gives 4,029 for Richardson
5,437 for Sedgewick
5,740 for French
But these numbers are dubious.
67th Tigers goes through the whole corps in a post:
http://67thtigers.blogspot.com/2009/08/strength-of-2nd-corps-at-antietam.html
And the estimate for effectives given by this analysis is on the order of 12,500.



4th Corps:
Not at Antietam itself on the 17th.



5th Corps
Carman estimates:
1,640 for Buchanan's brigade, but no supporting source can be found
The rest were not engaged.

It would be reasonable to say:
1,060 PFD for Lovell's brigade (not effectives),implying about 800 effectives
5th and 10th NY: unknown, but but small - the 5th NY history gives effective strength and the 10th at the same ratio would give them just 225. I'll use 500 however (25 per company).
(Sykes on September 2 in the Schulte ORBAT is 2,938 infantry, this gives them 2,940 which seems reasonable)
Morell: 5,407 PFD for the whole division, including artillery (two batteries of which were in Carman's count of engaged). This would indicate about 4,000 effectives, but the given PFD is lower than expected pre-straggling PFD by a couple of thousand (but then again Morell's division had marched all the way from Arlington to Antietam in five days, which would tend to induce straggling). I'll use 5,000 effectives as a broad figure, giving the whole of 5th Corps as just under 8,000 infantry effectives.


Humphreys was not at Antietam on the 17th.




6th Corps:

Franklin: Frankin said he had 8,100 effectives at South Mountain, and deducting 533 South Mountain casualties and assuming none of that figure is artillery gives 7,467 infantry effectives. This is an overestimate.



9th Corps
Carman gives 11,714, but several of the regimental strengths he uses are PFD. Again 67th has looked at this:
http://67thtigers.blogspot.com/2009/08/strength-of-9th-corps-at-antietam.html
And the rough number he has reached is about 8,400 infantry effectives.


12th Corps
Carman gives 7,239. This implies that 71% of PFD is infantry effectives, which suggests that it is high.



Artillery: Carman gives 5,982 engaged, and there was one battery of Morell which was not engaged in Carman's definition. Using 118 for ease of calculation gives 6,100.

Cavalry: Carman includes units off the field, but going through by companies estimates 2,636 cavalry on the field.

This gives a total of

52225 infantry
2636 cavalry
6100 artillery

For 61,000 effectives on the field.

If all corps got 62% of their PFD into line as infantry effectives the total strength on the field would be 58,499. This gives the general picture of the Union army being roughly 24%-30% stronger on the field than the Confederate one, though much of this would be in "green" regiments (there were 21 "green" regiments on the field at Antietam, inclusive of Morell but exclusive of Humphreys, and these would represent roughly 11,070 effectives at 62% of an average PFD of 850 - most or all of the difference in the army sizes)

Union corps​
PFD (pre straggle) at Antietam​
Inf eff at Antietam​
% of PFD as inf eff​
Notes​
1st​
13996​
8619​
61.58%​
This is the one we have the best information for​
2nd​
17953​
12500​
69.63%​
This one might still be high​
5th​
12930​
8000​
61.87%​
6th​
11440​
7467​
65.27%​
Known overestimate​
9th​
13819​
8400​
60.79%​
12th​
10126​
7239​
71.49%​
This one might still be high​
Green regiments​
17850​
11067​
62.00%​
62% by definition here​

It's worth noting at this point that the Union PFD on the field on the 17th was about 83,000.



I've already been largely alluding to it, but the next category is regiments of all arms. The figure for the Confederates is 2,015 companies (201.5 regiments of all arms), though only about 197 ROAA were at Antietam, and for the Union it is:

Corps​
Division​
Inf regiments​
Arty batteries​
Cav coys​
Total coys​
Notes​
Army​
Escorts etc​
1.6​
11​
27​
1st​
Doubleday​
17​
4​
174​
1st​
Ricketts​
12​
2​
122​
1st​
Meade​
11.7​
3​
120​
4 PA R has 5 coys, 13 PA R has 6, 2 PA R has 8, 10 and 12 PA R has 9​
1st​
Escorts​
4​
4​
2nd​
Richardson​
13.8​
2​
140​
69th NY and 52nd NY have 9 coys each​
2nd​
Sedgwick​
13.8​
2​
140​
1st MN has 11 coys, 72nd PA has 15, plus 2 coys of sharpshooters​
2nd​
French​
10​
100​
2nd​
Escorts​
3​
2​
5​
4th​
Couch (not present 17th)​
15​
4​
154​
Includes 139th PA, which joined 17th​
5th​
Sykes​
8.8​
3​
91​
68 total regular coys, plus Warren​
5th​
Morell​
20.2​
3​
205​
Extra coys of MI and MA sharpshooters​
5th​
Humphreys (not present 17th)​
8​
2​
82​
5th​
Escorts etc​
7​
2​
9​
6th​
Slocum​
11.8​
4​
122​
18th NY is 8 coys​
6th​
Smith​
14.4​
3​
147​
43rd NY is 5 coys, 3rd VT is 9​
6th​
Escorts​
2​
2​
9th​
Wilcox​
8​
2​
82​
9th​
Sturgis​
8​
2​
82​
9th​
Rodman​
7​
1​
71​
9th​
Kanawha​
6​
2​
1​
63​
9th​
Escorts etc​
2​
10​
12​
Includes 6th NY (8 coys)​
12th​
Williams​
11.1​
111​
Zouaves d’afrique just 1 coy​
12th​
Greene​
11.2​
112​
28th PA is 15 coys, but Purnell Legion/3 MD/109 PA are all 9​
12th​
Escorts etc​
7​
1​
8​
Averell​
31​
31​
10 coys 5th US, 4th PA, 9 coys 6th PA​
Pleasonton​
36​
36​
8th IL, 3rd IN, 1st MA​
Horse Art​
3.5​
3.5​
Half a battery with McReynolds​
Scattered other coys​
20​
20​
3rd PA, bn 12th PA, bn 1st US​
McReynolds (not present 17th)​
0.5​
32​
32.5​

For 231 regiments of all arms, of which 204 were on the field at some point on the 17th.



The final category is officers.

Number of Confederate officers on the reports:

September 22 (very imperfect): 2,732 (12.2 ORs per officer)
September 30: 3,857 (12.6 ORs per officer)
October 10:
4,540 (13.2 ORs per officer)
4,117 without the cav div (13.2 ORs per officer)


Union officers on the returns:

1st Corps September 18:
374 (16 ORs per officer)
1st Corps September 22:
666 (22 ORs per officer)

October 10 return (first with officers broken out)
5139 officers in the field (20.3 ORs per officer)


This supports the argument that the Confederate strength category "PFD" is not the same as the Union. If the average Confederate division had as many ORs per officer as the Union 1st Corps on the 22nd then the Confederate strength on the 22nd would be expected to be 46,444 PFD (officers and men) on that date (which is after casualties).




Conclusion

The exact strength on the field is hard to define, but there are these common threads:

The Union and Confederate army strengths were quite similar, and somewhat discounting the new green regiments means we can largely see the two armies as comparable in combat strength in Maryland (and indeed at Antietam itself). Any significant disparity in strength would result from what happens during the campaign (i.e. straggling).

Lee's decision to invade the North now actually makes sense. He had beaten an army significantly larger than his own at Second Bull Run, and subsequently been reinforced; he had no reason to think that in a "fair fight" he couldn't produce a win.

There is no data to support the idea that the Union force outnumbered the Confederates 2:1 by any consistent measure.
 

Saphroneth

Major
Joined
Feb 18, 2017
Special Order 191


The time that Special Order 191 passed into McClellan's possession


The exact time when SO 191 was found is not explicitly stated. There has been an argument in the past that it was found and passed to McClellan before noon, but the evidence for this is scanty. (It was promulgated perhaps first by Jacob D. Cox.)

There is a telegram to Lincoln in which McClellan says that he has captured the Confederate plans, and that he is in control of the passes in Catoctin Mountain. The "it was in McClellan's hands by noon" argument holds that this telegram (dated 12 M in the ORs) was sent at 12 Midday, but this does not hang together:

- The telegraph in the area had been destroyed, and at 1500 hours on the 13rd it had been re-established over the Monocacy River (connecting Frederick and Monocacy station) and it then needed to be relaid to Urbanna. Thus sending a telegram at noon would be impossible.

- As of noon, the Union had control of neither of the Catoctin passes. Braddock Heights (the National Road pass) was captured around 1PM, and Jefferson Pass was not captured until after 5PM when elements of the 6th Corps arrived to help the cavalry and 9th Corps elements already assigned to capture it.

- The regiment that found SO 191 went into bivouac around midday (per their commander) and it was after that that the envelope was noticed and it began heading up the chain of command. The first few jumps (Corporal Mitchell -> Sergeant Bloss -> Captain Kop -> Colonel Colgrove) were fairly quick because a regimental encampment is fairly small, but then it had to go to brigade HQ (to Gordon's HQ, where Kimball was also present) and then to divisional HQ.

Williams was absent and had to be fetched by runner, and this is also the period in which the signature was verified.

Kimball then went looking for McClellan's HQ, which wasn't established until between 2 and 3 PM at the Steiner Farm. McClellan returned to his HQ around 2:30 PM and by 3 PM he was sending a copy forwards to Pleasonton to verify it.

- This one should have been conclusive years ago, but the original telegram at the War Department says "12 Midnight" and the Time Recieved form reads "2/35 am".


What the Lost Order says


The Lost Order reads:


Special Orders, No. 191
Hdqrs. Army of Northern Virginia
September 9, 1862


(sections 1 and 2 are missing from McClellan's copy)
3 The army will resume its march tomorrow, taking the Hagerstown road. General Jackson's command will form the advance, and, after passing Middletown, with such portion as he may select, take the route toward Sharpsburg, cross the Potomac at the most convenient point, and by Friday morning take possession of the Baltimore and Ohio Railroad, capture such of them as may be at Martinsburg, and intercept such as may attempt to escape from Harpers Ferry.
4 General Longstreet's command will pursue the same road as far as Boonsborough, where it will halt, with reserve, supply, and baggage trains of the army.
5 General McLaws, with his own division and that of General R. H. Anderson, will follow General Longstreet. On reaching Middletown will take the route to Harpers Ferry, and by Friday morning possess himself of the Maryland Heights and endeavor to capture the enemy at Harpers Ferry and vicinity.
6 General Walker, with his division, after accomplishing the object in which he is now engaged, will cross the Potomac at Cheek's Ford, ascend its right bank to Lovettsville, take possession of Loudoun Heights, if practicable, by Friday morning, Key's Ford on his left, and the road between the end of the mountain and the Potomac on his right. He will, as far as practicable, cooperate with General McLaws and Jackson, and intercept retreat of the enemy.
7 General D. H. Hill's division will form the rear guard of the army, pursuing the road taken by the main body. The reserve artillery, ordnance, and supply trains, &c., will precede General Hill.
8 General Stuart will detach a squadron of cavalry to accompany the commands of Generals Longstreet, Jackson, and McLaws, and, with the main body of the cavalry, will cover the route of the army, bringing up all stragglers that may have been left behind.
9 The commands of Generals Jackson, McLaws, and Walker, after accomplishing the objects for which they have been detached, will join the main body of the army at Boonsborough or Hagerstown.
10 Each regiment on the march will habitually carry its axes in the regimental ordnance—wagons, for use of the men at their encampments, to procure wood &c.

Special Order 191's contents on the map, including the two most likely routes Jackson could take
SO191.jpg



The orders are for movements from Wednesday September 10th to Friday September 12th, in that "by Friday morning" is the operative phrase in sections 3, 5 and 6.

McClellan knows that Harpers Ferry has not yet fallen as of when he captures the orders, and he doesn't know if the orders have yet been changed. He does know however that if the orders have not changed then he can expect:

1 division to be southeast of Harpers Ferry
"Jackson's command" to be southwest of Harpers Ferry, though not necessarily close to it
2 divisions to be northeast of Harpers Ferry
And "Longstreet's command" plus DH Hill's division to be at or around Boonsboro.


This tells McClellan a few important things. One of them is that the Confederate army is divided, and another is that it at the same time gives him an opportunity and limits the damage he can really do:

Positions on the 13th. Strict reading of SO191 in red, true positions where different in orange.
SO191_13.jpg


Walker's force is south of the Potomac, and not far from the fords near Charlestown. If McClellan tried to trap Walker's division, then Walker could simply escape into the Shenandoah, and it's hard to get at Walker anyway.


Longstreet's force and DH Hill are at Boonsboro, and they have more than one possible line of retreat. If McClellan drove hell-for-leather at Boonsboro and Lee wanted to get that part of his army out of trouble they could (1) defend the mountain pass and then (2) withdraw over the Potomac via Shepherdstown (or other fords) and be fine - the greatest cost in that scenario would be the loss of the wagons which couldn't cross those fords in time, which would be painful for Lee but leave his army otherwise intact.


Jackson's force in the Shenanodah is completely inaccessible as things stand. To get to them would require McClellan to punch through either McLaws or the Main Body just to *reach* a crossing point where he could get at Jackson, and he'd then need Jackson to not fall back under those circumstances.


McLaws' force in the Pleasant Valley, meanwhile, is potentially vulnerable. The size of this force is not entirely certain from the information, but it's got to be sizeable (two divisions) and if the commander of the Harpers Ferry defences is doing his job and holding the Maryland Heights then there's a real chance to pin that force in the Pleasant Valley and destroy them; if not, so long as Harpers Ferry is held then the only escape route for McLaws' force is to march north between South Mountain and the Potomac (either side of the Maryland Heights) and this would in turn mean either that DH Hill and Longstreet have to hold the northern South Mountain gaps (i.e. stay there to be hit!) or that McLaws and Anderson could be captured.

The various ways McLaws has out of his position near Harpers Ferry, and the way Federal forces can block each of them.
trap_McLaws.jpg




McClellan's decisions


What McClellan does first after sending orders to his cavalry to verify the information with observations from the front is to confirm in writing his verbal orders to Cox and 9th Corps (which were to push west to Middletown in support of the cavalry advancing into the valley between Catoctin Mountain and South Mountain). This basically occupies the road out of Frederick for the rest of the afternoon and evening, and indeed into the night.
Once the Jefferson Pass has been captured, McClellan has the rest of the 6th Corps conduct a night march to Jefferson Pass, and issues orders for various components of his army to move at sunrise.

His intent is to push most of his force via Frederick to hit the main South Mountain gaps, and to have 6th and 4th Corps (i.e. 9 brigades) attack Crampton's Gap to try and trap McLaws.

McClellan's movements in response to SO191
SO191_14.jpg


Late on the 13th, Captain Russell of the 1st Maryland Cavalry was sent out of Harpers Ferry with a message to the effect that Harpers Ferry could hold out only for 48 hours (i.e. until late on the 15th). McClellan got this message and sent a reply by three different couriers to the effect that a relief force was en route, but this message may not have reached Miles. (There is a question about whether Captain Henry Cole carried a message from Miles to McClellan and then returned with a message from McClellan by the evening of the 14th, which would have either meant Miles knew there was relief nearby or that Cole failed to pass on the message.)



On the 14th, around 9AM, the Union attack on the Confederates along South Mountain began. This reflects a pretty impressive level of "rush", all things considered, because from the longitude of Frederick to the longitude of South Mountain is about 10-12 miles (i.e. a typical day's road marching in and of itself), though 6th Corps didn't "rush" quite so much and took much of the day to arrive. They were however opposed to a force roughly equal in strength to their own (most though not all of McLaws' "corps", the whole being a ten-brigade force), so it's understandable why Franklin would want to wait until he'd got a lot of his troops concentrated before attacking.

The fighting at South Mountain was bloody and costly, and the Union forces made progress but were unable to gain the gap by the end of the day.

Franklin meanwhile *was* able to successfully gain the gap by the end of the 14th, but didn't have the time to get troops over the gap and then advance before the end of the day, so advanced down the Pleasant Valley on the morning of the 15th.
It is highly likely that Miles could have known about the firing that was going on at Cramptons Gap. Jackson's men overheard the firing, and so did the colonel of the 65th Ohio (in Harpers Ferry). Despite this, however, when the Confederate cannonade began (around sunrise) and Jackson prepared an assault, and even though it was well before the 48 hour timeframe he'd given McClellan, Miles surrendered the garrison.

Franklin was advancing until the gunnery stopped, and so it seems plausible that if Miles had held out until even midday on the 15th he would have been relieved and McLaws' forces either trapped in the Pleasant Valley or at risk of being cut off by McClellan's movements. As it was, however, the surrender at Harpers Ferry let McLaws cross south of the Potomac.





Meanwhile, on Lee's side of things, Lee probably became aware that McClellan had got hold of a copy of at least some of his orders early on the morning of the 14th - something he apparently found out when reported by Stuart at that time (via dispatch). This and the fighting led to the following course of events (per Harsh).
Stage one: Longstreet marches to Boonsboro, and there is the battle of South Mountain.
Stage two: War council at 8PM 14th September.
Lee decided to abandon the Maryland Campaign. The part of the army with him is to return to Virginia, while McLaws is to get his force over the Maryland Heights, march north to around Sharpsburg and return to Virginia that way. The Harpers Ferry siege is to be abandoned.
Stage three: Lee discovers the results of the Union attack on Crampton's Gap (around 10PM), and that McLaws has not managed to hold them off. Lee changes plans again to temporarily hold the Main Body (Longstreet + DH Hill) at Keedysville to secure McLaws' flank.
Stage four: At Keedysville at sunrise on the 15th (around 6AM), Lee decides to keep moving west over Antietam Creek and make his stand at Sharpsburg.
Stage five: En route to Sharpsburg, Lee got a dispatch from Jackson of the previous evening where he predicted that Harpers Ferry would soon surrender.
Stage six: at noon, Lee heard that Harpers Ferry had surrendered. Lee's plan changes to staying in Maryland at this point, though it's not clear for how long.


For a significant chunk of time, Lee was ordering McLaws to abandon the siege with increasing urgency, and had McLaws and Jackson obeyed orders this is exactly what would have happened (and Harpers Ferry would have survived); had they disobeyed/ignored the orders as they did, but Miles held out for as long as he said he would, then McLaws would likely have been cut off and compelled to surrender. Only the combination of Jackson and McLaws' intrasingence and Miles' failure (both in retaining control of Maryland Heights and in not holding out for the 48 hours he said he would) resulted in a Union surrender and a Confederate escape.

McClellan's operational movements (i.e. where to march) in exploiting Special Order 191 are almost as good as they could feasibly have been. There are some problems in execution, perhaps - Couch could have been sent along the Potomac river road to threaten at Weverton Gap, depending on the prospects of actually capturing that gap, and 6th Corps could have moved overnight somewhat (though since they ended the 13th with most of their force at Buckeystown they'd have had to do a lot of night marching to get most of two divisions to Crampton's Gap by, say, noon on the 14th).

The idea that McClellan delayed for 18 hours between getting hold of SO 191 and moving is completely false. He had troops on the move straight away gaining and moving to mountain gaps, and even though 12 of those purported 18 hours are during the hours of darkness 9th Corps is moving during that period (getting through Frederick, particularly the wagons) and 1st and 6th Corps are awake or moving for some of it; McClellan simply can't cram his entire main body on a single road and move it 10 or 12 miles in a single afternoon.

There is however a possible argument that McClellan should have cut away from his wagons and marched for Turner's Gap without supply. This could have been done, but would have meant that the troops were carrying three days' rations (for the 13th, 14th and 15th) and badly limited their endurance after South Mountain had been taken; it would perhaps mean a higher chance of catching McLaws (assuming things were going right at Harpers Ferry to permit such a thing happening) but a much lower chance of doing anything useful beyond that.
 

Saphroneth

Major
Joined
Feb 18, 2017
Actions from the fall of Harpers Ferry to the morning of September 17


With Harpers Ferry fallen, Franklin went firm and stopped attacking. This was probably not the wrong decision, though attacking could have achieved some minor dividends.

Lee meanwhile was pulling back from South Mountain overnight to Sharpsburg (having originally planned to pull back to Keedysville) and his wagon trains were crossing the Potomac. Some of them got intercepted by Union cavalry that escaped from Harpers Ferry, but that doesn't really have a bearing on McClellan's actions.

With McClellan's main column, on the morning of the 15th, the fundamental problem was that the lead corps (1st and 9th) had had a very long day and were badly tired out. Meanwhile everything else was stacked behind them on the road, with the rough situation being:
9th Corps at Fox's Gap
1st Corps at Turner's Gap, supported by Richardson's division
The remaining two divisions of Sumner's 2nd Corps and Sykes' division were stacked up behind them on the National Road
And 12th Corps was still departing Frederick, with Morell behind them. Humphreys was still far too far behind to reach them.

Note that at this point the "wing integrity" of McClellan's wings is still pretty solid, but that's about to change.

McClellan's orders to Hooker are to send Richardson's division through (presumably as a fresh unit) and then follow in pursuit towards Boonsboro, supporting the cavalry who are the vanguard of the pursuit.
His orders to 9th Corps are to swing south somewhat and support 6th Corps in moving in "either direction" (which two these are is not clear) or if required advance to Centerville (Keedysville) and Sharpsburg to cut off the retreat of the enemy. The orders also specified that because Hooker and Burnside were being separated they'd both report directly to HQ for now.
Sumner with his remaining divisions of 2nd and 12th Corps was to follow Hooker, and Sykes was to follow 9th Corps through their gap; possibly also Morell was to follow 9th Corps.

His orders to Franklin, meanwhile, envisaged first making contact with Miles (who hadn't yet surrendered when the order was written) and absorbing the troops at Harpers Ferry, then turning north and either joining in McClellan's attack at Boonsboro or, in the event that the enemy retreated to Sharpsburg, to "fall on him" and cut off his retreat. This column moved towards Harpers Ferry, then (as mentioned) went firm when the garrison surrendered.

The column led by Richardson was engaged shortly after sunrise around Boonsboro, fighting F. Lee in and through the town itself by 8AM.

Cox delayed considerably after getting the order (in his write up of the situation after the fact he claimed that he didn't get the order to move until nearly noon), so when Sykes arrived he pushed through first. It is not clear whether Burnside or Cox erred, but the formal written order to Burnside was to "advance with your whole corps upon boonsborough" and was dated 8AM; if Cox says he didn't get the order until nearly noon, either Burnside erred in not passing it on or Cox erred in not following it.


Given the configuration of the troops at the time, having reached South Mountain, McClellan doesn't really have any options which would preserve the degree of haste he was aiming for without splitting up at least one wing (if not one corps). 1st Corps and 9th Corps are the corps which are at the gaps, and while passing Richardson through is doable passing the whole of 2nd Corps through would add hours of delay, and would still split up Sumner's wing unless 12th Corps followed them, while having Sykes be the force that turned south to cooperate with Franklin would be a much smaller force than 9th Corps and not really fitting with McClellan's intent.


McClellan's two lead divisions (Sykes and Richardson) ended up essentially pursuing to the bank of the Antietam, where they found Lee had "gone firm" and set up in a defensive configuration over the main road (or "Middle") bridge. They deployed into line facing the creek more or less on their own authority on the afternoon of the 15th.
Meanwhile 9th Corps was slowly moving through Fox's Gap, and an enormous column (1st Corps, two divisions of 2nd Corps, all of 12th Corps, and then Morell behind them) was being fed through Turner's Gap.
It's during this period that a large number of Confederate prisoners appear to have been swept up, stragglers run down on the road by the pursuing Union infantry and cavalry.



When McClellan arrives there in the afternoon, on the Confederate side of Antietam Creek (discounting cavalry on both sides) there are:

Longstreet (557 coys)
DH Hill (232 coys)
Pendleton's reserve artillery (19 coys)
For a total of 808 coys.

The Union side has:

Sykes (91 coys)
Richardson (140 coys)
For a total of 231 coys.

Attacking is obviously a bad idea, even before considering the terrain.

In the area of the Antietam battlefield there are broadly speaking three bridges, Upper, Middle - the main road bridge - and Lower (going north to south, which means right to left for the Union side).
Sykes and Richardson followed Lee through Keedysville and down the main road and deployed facing the Middle bridge, and on the far side Lee's army was drawn up in a defensive position on the heights over the bridge. This is a fairly gentle slope, but what that also means is that it's good terrain for defensive artillery fire, and with only one attack route there are certain shades of Malvern Hill which the terrain brought to mind. (Malvern Hill had been at the end of June, meaning less than three months previously.)

McClellan thus does not attack; I think it's almost impossible to argue he should have done, given the situation. He begins pulling in his troops in general, and there's nearly a mistake here because at least one corps accidentally takes the Hagerstown road at Boonsboro until corrected.

Of the remaining forces:

Northern column

1st Corps (head of column behind Richardson) is directed to move to the Upper Bridge, where they arrive at last light and not in any order.

2nd Corps (Sedgwick and French) and then 12th Corps are still marching to the field.

Morell is significantly behind them all.

9th Corps meanwhile has been moving slowly. It was in the Pleasant Valley, facing south towards Harpers Ferry.




My understanding of McClellan's operational thinking at this point (late 15th and overnight) is:

Lee is at Sharpsburg with part of his army, and the rest of his army is at Harpers Ferry. Since the town has surrendered, McLaws and Anderson can be reinforced by Jackson's command and Walker's division, so I need to be prepared in case Lee throws the majority of his effort at me from Harpers Ferry.

The portion of Lee's army which is at Sharpsburg (currently DH Hill and Longstreet) is one which he could reinforce with the rest of his army. I do not currently have the strength available to attack it, and it is an avenue through which he could continue his invasion of the north, but he would not be able to move north on the 16th without that splitting his army.

Lee may also be intending to retreat south of the Potomac and end his invasion. In this case I do not currently have the strength ready to fight to prevent him.

I do not think Lee is currently likely to send force east along the Potomac from Harpers Ferry, because it would split his army. If he is planning on doing this he would first pull south of the Potomac, and I can replan then.

I will plan an attack on the Confederate troops at Sharpsburg.
(That last bit is suggested to me by McClellan sending 1st Corps to the upper bridge, which is the only bridge over which he can move troops unmolested as Lee does not have troops controlling it.)


What Lee was thinking

It's a little harder to be sure, but it's my belief that there are four possible options for what Lee was thinking and planning. He may have had more than one of them in mind.

Option one is that he intended to stand at Sharpsburg and fight there so as to allow his wagons to escape (an ongoing process at the time, as the wagons take so long to cross - days, in fact) and was intending to end his invasion of the North.

Option two is that he intended to stand at Sharpsburg and fight there so as to allow his wagons to cross, to then follow them to Williamsport and re-invade the North there.

Option three is that he intended to stand at Sharpsburg and fight there to allow his wagons to move to Williamsport, but that he was then going to march north out of Sharpsburg and up the Hagerstown pike (and thus continue his invasion of the North).

And option four is that he simply saw an opportunity to inflict losses on the Union army, possibly in a similar way to Jackson absorbing damage at Second Bull Run.


One thing that is a constant in all of these, however, is that Lee saw the risk associated with staying north of the Potomac at Sharpsburg to be worth it. There is no sense in which Lee is actually required to stand at Sharpsburg except in service of his goals, and if it were a matter of the preservation of his army then Lee could (and would) retreat south of the Potomac, for example overnight on the 15th-16th.




Morning of the 16th

Overnight on the 15th-16th and on the morning of the 16th, Lee called for reinforcements from Jackson. Jackson's division marched through the night and straggled to pieces (down to about 10 men per infantry company when measured shortly after arriving, though they recovered considerably later), while Ewell's division moved somewhat slower and held together considerably better. These units (41.6 regiments) arrived in the rear at dawn; Walker's division (9.2 regiments) crossed the Potomac at noon.

Positions late on the 15th/dawn on the 16th.
16th_Dawn.jpg



Fog on the morning of the 16th made it unclear at first what the Confederate positions were, but by noon McClellan had a plan assembled:

Sykes and Richardson were to hold position for now as McClellan's centre.
Burnside was to bring the 9th Corps to the southern bridge over the Potomac, thus becoming McClellan's left.
To the right, meanwhile, Hooker was to push the 1st Corps over the Upper Bridge (and associated ford) and to block the Hagerstown Pike to the north, a move which was considered reckless at the time by Hooker (among others). Sumner was told to bring his wing, and it appears at this point that McClellan had not yet decided whether to use the 2nd Corps on his centre, right or (conceivably) left; 12th Corps would end up being ordered to follow Hooker once they were at Keedysville, and 2nd Corps were at first held east of the Antietam.

It is possible that McClellan might have attacked on the 16th if both 9th and 12th Corps had arrived in time to get involved in the fighting, but as it happened both corps arrived too late to get involved in the fighting that day. 12th Corps was approaching Keedysville around sundown (1800 hours), and only one division of 9th Corps reached the lower bridge by sunset.

Assuming that McClellan prioritized speed above everything else, he could have redirected French and Sedgwick to follow Hooker and had 12th Corps marching to the Middle Bridge instead; if 12th Corps had marched faster (it's hard to see how without McClellan supervising them personally) then they could have got involved late on that day by marching over the Middle Bridge around sundown (allowing perhaps an hour of fighting). Meanwhile if 9th Corps had marched faster (again, probably requiring McClellan's personal supervision) they could have reached the Lower Bridge in time for a crossing before the end of the day.

Depending on what units get involved, here are the prospects for fighting on the afternoon of the 16th:



Union units (includes Army HQ escort but not formed cav)​
Union ROAA​
Confederate ROAA (Longstreet, DH Hill, reserve artillery, Stonewall, Ewell, Walker, not cav)​
Union advantage​
Sykes, Richardson​
25.8​
131.6​
-80.40%​
S, R, 1st Corps​
67.8​
131.6​
-48.48%​
Sykes, 1st Corps, 2nd Corps​
92.3​
131.6​
-29.86%​
Sykes, 1st Corps, 2nd Corps, 9th Corps​
123.3​
131.6​
-6.31%​
Sykes, 1st Corps, 12th Corps​
115.4​
131.6​
-12.31%​
Sykes, 1st Corps, 9th Corps, 12th Corps​
146.4​
131.6​
11.25%​

With the Confederates on good defensive terrain - bluffs over the Antietam - it is by no means certain of a good result, to put it lightly.


The movement by Hooker served an additional purpose, however, which is that it blocked Lee's road north. This meant that Lee's only immediate options at Sharpsburg were to endure a Union attack or slip south of the Potomac overnight.


As of the evening of the 16th, McClellan had probably already put together the basic attack plan he would use on the morning of the 17th. He was in a position where all he would need to do to have the invasion of the North end would be to stand in position, and Lee would be either trapped in a small triangle of land in Maryland or retreat south of the Potomac.

Instead, McClellan committed 1st Corps, 12th Corps and two divisions of 2nd Corps (slightly under 100 regiments of all arms) to make an early attack in the north, with Richardson's division of 2nd Corps remaining in the centre as his reserve (at least until Morell showed up in the morning and replaced Richardson as his reserve). In accordance with this 12th Corps was ordered to cross on the evening of the 16th (they end up crossing hours after this) and Sumner was to be ready to cross the Antietam before dawn on the 17th, but there was a delay resulting from the mess of French's thrown-together division.
Sykes was to form the army centre and push over the river there, while 9th Corps was to attack over the Lower Bridge an hour or two later (to be ready to go, and triggered on McClellan's orders).


The operational intent of this attack sequence is that it places Lee in a fork (of the chess type). The strong attack from the north is intended to be powerful enough that Lee can't effectively defend against it without committing troops from his southern flank (or stripping his centre), while Burnside's movement is one which carries the threat of cutting Lee off from the Potomac.
Thus:

If Lee strips his centre bare to respond but does not weaken his right, then Sykes and Richardson (later Sykes and Morell) can advance against the stripped centre.
If Lee strips his right to respond, then Burnside can get over the Lower Bridge and envelop Lee's right.
And if Lee does not strip his centre or right, then the attack in the north can make headway and inflict heavy casualties.

Since it is the attack over the Lower Bridge which has the greatest prospects for success, it could be argued that McClellan should have more heavily bolstered this attack. I think however that this isn't really feasible, firstly because the forces bolstering that attack have to come from somewhere (and all the forces McClellan has available are committed elsewhere, meaning that the forces to more heavily bolster the Lower Bridge attack would have to come from Hooker's assault - that is, make that "distracting" attack weaker), and secondly because the Bridge is a defile that a force has to move over to capture it and once captured. There is no space for any additional troops beyond Burnside's 9th Corps to help in capturing the bridge.

There is the prospect of course of McClellan committing his reserves to cross the Lower Bridge after it has been taken, to lend force to that attack, but the time it is expected to take to get 9th Corps over the bridge is such that there will be time to make that decision if it seems warranted.


Overnight, McLaws and Anderson arrive on the Confederate side of the lines (bringing the Confederates up to 162 regiments of all arms), and in the early morning McClellan orders Franklin to march to the field with two divisions while Lee orders AP Hill to do much the same thing with most of his (larger) division. This means the current states are:


Confederates at Sharpsburg: 162 regiments of all arms exclusive of cavalry
Upper bridge attack force, Union (1st Corps, 12th Corps, 2nd Corps minus Richardson): 89.6 regiments of all arms
Force at middle bridge (Sykes, Richardson, art res, army troops): 26.5 regiments of all arms
Lower bridge attack force (9th Corps): 31 regiments of all arms
Total at Sharpsburg: 162 Confederate, 147 Union

Marching to the field
(Union):
Morell : 20.5 regiments of all arms
Franklin (Smith leading Slocum): 27.1 regiments of all arms
(Confederate)
AP Hill minus Thomas: 22.7 regiments of all arms

At Harpers Ferry:
Couch: 15.4 regiments of all arms
Thomas' brigade: 4 regiments of all arms


Humphreys, with 8.2 regiments, is far too far away to arrive in time.


This is quite aggressive.


It is worth pointing out however that McClellan could have ordered Franklin to march along the southern side of the Potomac instead. This would have meant a second Union column independently trying to get between Lee and the Potomac, but it would also mean that the attack in the north (by ultimately about 103 regiments of all arms) was supported by minimal reserves and as the attack actually developed it would have resulted in fewer troops to shore up the Union line there; it would also have been unnecessary if Burnside had carried the Lower Bridge.
Effectively this option (Franklin to the "Iron Works bridge") is a good idea if the attack in the north is expected to go well (enough not to need or benefit from reinforcement) but the attack in the south is expected to fail.

16th_Dawn.jpg
 

Saphroneth

Major
Joined
Feb 18, 2017
Whoops!

I've just noticed that the org chart I've been using for the number of companies/regiments in recent posts has been based on the Second Bull Run order of battle, not the Antietam one itself. The key impact this has is on the size of units such as the force of "McLaws and Anderson" and the size of Longstreet's force at Antietam on the 15th and 16th.

I'll be redoing those calculations accordingly.
 

Saphroneth

Major
Joined
Feb 18, 2017
So in putting together the information, these issues have come up:

The 2BR ORBAT I'm using:

Has the 5th VA Bn, which disbanded and the men transferred to other units.
Does NOT have the 3rd SC Bn, and consequently I have no effective strength or number of companies for it.
Lacks the Wise artillery (which was at Second Bull Run and also fought at the Lower Bridge)
It lacks the 49th VA, part of Early's brigade.
It also lacks the Madison artillery, Magruder's artillery, and Leake's battery left at Leesburg.

For the purposes of company counts, I will assume all four mentioned artillery are one company (but 0 str as I have nothing to go on). I will assume the 49th VA has 10 companies and is of a typical strength for Ewell's division (30 effectives per company).
 

Saphroneth

Major
Joined
Feb 18, 2017
New company assessment:


Unit Name
Strength
Cos.
Eff per coy​
PFD per coy​
Army of Northern Virginia / General Robert E. Lee
72541
2030
35.7​
44.7​
McLaws’ Command
18727
430
43.6​
54.4​
McLaws' Division / MG Lafayette McLaws
7765
164
47.3​
59.2​
Anderson's Division / MG R.H. Anderson
10962
266
41.2​
51.5​
Longstreet's Command / MG James Longstreet
14099
430
32.8​
41.0​
Jones' Division / BG D.R. Jones
8611
279
30.9​
38.6​
Hood/Evans
4835
141
34.3​
42.9​
Hood
3839
92
41.7​
52.2​
Evans
996
49
20.3​
25.4​
Longstreet Res Art
653
10
65.3​
81.6​
D.H. Hill's Division / MG D.H. Hill
6621
232
28.5​
35.7​
Walker
5159
92
56.1​
70.1​
Jackson and Ewell
12191
426
28.6​
35.8​
Stonewall Division
5513
198
27.8​
34.8​
Ewell’s division
6678
228
29.3​
36.6​
A.P. Hill's "Light" Division / MG A.P. Hill
8429
265
31.8​
39.8​
Reserve Artillery / BG W.N. Pendleton
1312
22
59.6​
74.5​
Cavalry Division / MG J.E.B. Stuart
5664
127
44.6​
55.7​
Left at Leesburg
339
6
56.5​
70.6​
 

Saphroneth

Major
Joined
Feb 18, 2017
Assessment of what people saw:

Observation​
Number​
Companies​
Men per coy​
Whole army, September 4-6, said by a Virginia captain in Leesburg​
84000​
2030​
41.4​
Whole army, September 8​
75000​
2024​
37.1​
Whole army, September 9, Rebel deserter​
100000​
2024​
49.4​
Whole army, September 9, telegraph operator, over 100,000​
100000​
2024​
49.4​
Whole army, September 10, newspaper, 60,000 to 100,000​
80000​
2024​
39.5​
Main Body (Jackson Longstreet McLaws Anderson res art), September 10​
60000​
1573​
38.1​
Main Body (Jackson Longstreet McLaws Anderson res art), September 10​
70000​
1573​
44.5​
Main Body (Jackson Longstreet McLaws Anderson), September 10, “40,000 to 60,000”​
50000​
1573​
31.8​
Walker​
6000​
92​
65.2​
Jackson, Williamsport, “15,000 men and 70 pieces of artillery”​
15000​
691​
21.7​
Jackson, south of Williamsport, “not less than 25,000”​
25000​
691​
36.2​
Jackson, 6 miles west of Williamsport, “15,000 infantry, 100 cavalry, 40 pieces of artillery”​
15000​
691​
21.7​
Jackson, west of Martinsburg, “with a force of 20,000”​
20000​
691​
28.9​
McLaws and Anderson, “30,000 men at Burkittsville”​
30000​
430​
69.8​
McLaws and Anderson, “25,000 down to 12,000”​
18500​
430​
43.0​
Anderson, “8,000 or 10,000 of the enemy”​
9000​
266​
33.8​
McLaws and Anderson, “some 30,000 of the enemy’s troops on the heights”​
30000​
430​
69.8​
McLaws or McLaws and Anderson, “I thought there were some 12,000 or 15,000, perhaps more”​
13500​
430​
31.4​
Longstreet’s Command, “20,000 to 30,000”​
25000​
430​
58.1​
McLaws and Anderson passing over from Maryland Heights, counter gave up after counting 17,600 infantry in 22 regiments averaging about 800​
17600​
430​
40.9​
McLaws and Anderson passing over from Maryland Heights, “20,000, perhaps 30,000”​
25000​
430​
58.1​
Total attacking force at Harpers Ferry (Jackson, McLaws, Anderson, Walker) “amounting in all to 40,000”​
40000​
1213​
33.0​
The amount of companies Steiner saw is effectively unchanged (delta of less than one regiment).


Assessment of attack prospects on the 16th:

Union units (includes Army HQ escort)​
Union ROAA​
Confederate ROAA (Longstreet, DH Hill, reserve artillery, Stonewall, Ewell, Walker, not cav)​
Union advantage​
Sykes, Richardson​
25.8​
120.2​
-78.54%​
S, R, 1st Corps​
67.8​
120.2​
-43.59%​
Sykes, 1st Corps, 2nd Corps​
92.3​
120.2​
-23.21%​
Sykes, 1st Corps, 2nd Corps, 9th Corps​
123.3​
120.2​
2.58%​
Sykes, 1st Corps, 12th Corps​
115.4​
120.2​
-3.99%​
Sykes, 1st Corps, 9th Corps, 12th Corps​
146.4​
120.2​
21.80%​
(This does not deduct the two regiments left at Martinsburg, but that's less than 2% of the Confederate force and is not far off being negligible)
 

Saphroneth

Major
Joined
Feb 18, 2017
In order to address the impact of McClellan's decisions on Antietam itself, it is probably best to consider the following topics.

- The initial attack (1st and 12th Corps) and Lee's reaction

- Reinforcements (arriving and sent over)

- Burnside and the Lower Bridge



Timeline:

Hooker's attack (around dawn, to 8AM) - initial Union success

Before 7AM - Cox moves Rodman's division away from the Lower Bridge to find a ford (Rodman's being the only division at the bridge) at Burnside's orders, leaving just the 11th CT.
It appears to be that the ford they were originally meant to cross (not Snavely's, the "Farm Ford" which is much closer to the lower bridge) was considered impassible because it was defended. It is passed by a brigade once the crossing is unopposed.

Before 7AM - McClellan sends warning order to Burnside, telling him to be ready to attack/move his force to the bridge (which is basically a reiteration of the orders from the 16th) but not to attack until ordered (This is Cox's account of what Burnside told him)

7:20 AM: Sumner starts French and Sedgwick moving to reinforce the Federal right

8AM - Lee commits his entire reserve (McLaws and Anderson) and strips Walker from the south
8AM - McClellan sends an order to Burnside to attack immediately (Lt James Wilson carried this)
Around 8AM: The 11th CT drives in Rebel pickets on the eastern bank of the Antietam at the lower bridge.

8:30 AM - Hooker and Mansfield are known to have gone down

Before 9AM: Crook's brigade of 9th Corps were ordered forwards, but got lost
Before 9AM: Cox is ordering Sturgis' division forwards
9AM: Head of Smith's division reaches McClellan's HQ, they are sent to the right at some time near here
9AM: Burnside orders assault against the Lower Bridge, only one regiment is present (11th CT) and they are repulsed
9AM: Sturgis starts moving to the Lower Bridge

9AM-9:30 AM - McLaws etc. get into the fight
9:10 AM: McClellan reiterates the 8AM order to Burnside (Col Sackett carried this)
9:10 AM: signallers at Red Hill observe the Confederate reinforcements, McClellan sends a warning to Sumner but it arrives too late

Around 9:10: the West Woods and Sunken Road fights begin (Sedgwick and French), beginning a 90 minute long crisis on the Federal right; McClellan will move over there to supervise
9:30 AM: McClellan commits Richardson to the right as Morell comes into view

10AM: Smith's division is engaged on the right, arriving just as a Rebel counterattack steps off; they prevent the attack from going in as the Confederates rethink charging formed troops.
10AM: 1st regiment of Nagle's brigade (2nd MD) charge the Lower Bridge and are repulsed
10:30 AM: 2nd regiment of Nagle's brigade (6th NH) charge the Lower Bridge and are repulsed, Sturgis decides to push artillery onto the heights to gain control of the bridge
10:30 AM to 11 AM: the crisis on the Federal right is fully finally resolved. Large chunks of 1st, 2nd and 12th Corps are ruined, but there is a solid line.

11AM: Slocum's division joins the right, Morell's division is closed up and in reserve
11AM: artillery begins bombarding the Confederates defending the lower bridge, and they pull out their guns once this happens

11:30 AM: Toombs pulls out his infantry from the Lower Bridge as well, leaving just a few pickets

Around noon, order of events not quite clear: McClellan returns to his HQ at the middle bridge, sends a fourth and very emphatic order to attack to Burnside (carried by Colonel Key) with a sealed order relieving Burnside and placing Morell in charge of 9th Corps in the case he doesn't follow it.
12:30 PM: Ferrero gets two regiments to charge and takes the bridge

2PM: AP Hill arrives at Boteler's Ford. This is seen by signallers and the warning is relayed to Burnside ("Yes; they are moving now a strong force of infantry from Shepherdstown into the woods west of Sharpsburg and northerly to our right."), but Burnside doesn't forward it to Cox who is exercising actual command


Around 3PM: McClellan returns to the right to settle an argument about whether to attack again (Franklin pro, Sumner against). McClellan sends for two brigades of Morell's division, which is basically his entire remaining reserve.
Around 3PM: 9th Corps marches onto the heights and attacks; another warning is sent to Burnside to "look out well on your left".

3:30 to 3:40 PM: AP Hill's division attacks, routing the 9th Corps

4PM: McClellan returns to his HQ again (seemingly having got news of Hill routing Burnside) and countermands Morell's movement as he goes past them, pulling them back to his centre.
Also around this time: Burnside is asking for reinforcements, and McClellan sends 1 battery plus Warren's small brigade. Burnside puts both into defensive positions around his HQ.

6:20 PM: McClellan tries to arrange a counterattack (Burnside on the left, Morell and what of Sykes can advance in the middle to align with Burnside's right flank); Burnside insists he's too weak to do so, and the fighting ends.



The initial attack

The coordination of the initial attack was less than it could have been. This is probably partly attributable to Hooker (who did not properly incorporate 12th Corps into his movement), partly attributable to Mansfield and 12th Corps (who were hours late getting over the river) and partly attributable to McClellan to the extent that he had the ability to check whether his orders were being followed or his orders were incomplete.

The somewhat late addition of two divisions of 2nd Corps to the attack was again partly attributable to McClellan (to the extent he could have done better in checking whether 2nd Corps was ready to move as ordered) but what this starts to point to is the biggest problem at Antietam - there's only one McClellan and he's needed in several places.

Despite these failures of coordination, however, the initial attack is one that Lee considers critically dangerous. The attack opens with the Confederate positions being:
Left - the Stonewall division (4 brigades), Ewell's division (4 brigades), Hood's division (2 brigades)
Left and centre: DH Hill's division (3 brigades facing the left, 1 brigade on the left facing the centre, GB Anderson's brigade facing the centre)
Total on the left: 4+4+2+4 = 14 brigades

Reserve: McLaws and Anderson's divisions (coming up from the fords at daybreak, 10 brigades)
Centre: Evans' brigade (1 brigade)
Centre and right: DR Jones' division (GT Anderson and Garnett on the centre, Jenkins/Drayton/Kemper on the right, Toombs brigade emphatically on the right)
Right: Walker's division (2 brigades)

Total in the centre: 1+1+2 = 4 brigades

Total on the right: 4+2 = 6 brigades

Total in reserve: 10 brigades.

By 9AM, Lee has committed his entire reserve on his left (except for one brigade, Armistead), and has pulled Walker's division from the right to contribute to the fighting on the left. In addition the fighting has pulled in all of DH Hill's division, and Lee has committed GT Anderson's brigade on his left.

This means that by 9AM, Lee's distribution of troops is:

Total on the left: Stonewall (4) + Ewell (4) + Hood (2) + DH Hill (5) + McLaws (4) + Anderson minus Armistead (5) + GT Anderson (1) + Walker (2) = 27 brigades. (Effectively 125-130 regiments)
Total in the centre: Evans, Garnett (2 brigades) = 2. (Effectively ~10 regiments)

Total on the right: Toombs (1, forward) + Jenkins/Drayton/Kemper (3, back at Sharpsburg) = 4. (Effectively ~23 regiments)

Total reserves: 1.


While Jenkins, Drayton and Kemper are theoretically available to defend either against an attack in the south or an attack in the centre (I have counted them as on the right because of their facing, but they are at Sharpsburg itself) they can't forward-deploy to oppose a crossing by Burnside because this would open up a large gap in the Confederate centre.


Thus, the initial attack did exactly what it was intended to do. Lee committed over 3/4 of his army by brigades/regiments to the northern sector, which indicates that the attack was so threatening that he felt he had no option to do anything else.




McClellan's commitment of reserves

The crisis that develops on the right (which is a crisis for both commanders) is such that McClellan ends up committing most of his reserves in the morning, firstly to increase the strength of the attack and then secondly so he can continue to pose a threat.
McClellan's concept of operations had two possibilities for how it could go, and by 9AM or so it is obvious that the option where Lee's strength is still largely focused to the south is not a possibility. Lee is deploying so much strength north that the second option (to pull Lee's force north and then attack in the south) is the one which is happening, more or less through lack of other possibilities.
However, in order for this to work McClellan has to deny Lee the option of interior lines - this meaning he has to make sure Lee can't fight off the attacks in the north, and then turn around and fight in the southern sector as well. To achieve this McClellan has to avoid exhausting or using up all his available troops in the north, and ideally in the centre as well - if McClellan is still presenting a viable attack threat then Lee has to respect it.

There's another reason why McClellan would want to have some unfought troops in the north as well, which is that the intense fighting has done a lot of damage to the Confederates but it's also done a lot of damage to the Union. 1st, 12th and much of 2nd Corps are effectively shattered and combat ineffective, with one division (Ricketts) estimated at only 300 effectives on the field from 122 companies on the afternoon of the 17th (implying about 2-3 men per company). It's the worst hit one we have data for, but several other divisions may have been largely destroyed.
The existence of the fresh divisions of 6th Corps not only presents threat but poses a viable counterattack/defensive option if Lee decided to push in the north. It was only the 30th August (less than three weeks prior) that a Union army had exhausted itself attacking and then the Confederates had launched a counterstroke that routed the army, so this is not an abstract possibility.


I think it is quite plausible that McClellan may have initially intended to keep more reserves on hand in the centre, but given what actually happened I think his choice was reasonable, and he still had enough strength elsewhere to conduct his plan.


For Lee, meanwhile, given that his initial counteroffensive was stopped by the arrival and deployment of Smith's division (around 10AM) I think it is plausible that Lee was actively planning on using interior lines (to fight in the north and then return his attention to the south) and that the deployment of 6th Corps stymied this. This would explain why Lee reportedly considered a counteroffensive at one point - he would be aiming to resolve the situation in the north sufficiently that he could redeploy troops south.



An additional point worth noting is that Lee pulled some of his hardest hit units out of the line and had them gathering up stragglers, with several thousand gathered by the evening. The extent to which these units with an ad-hoc organization and already fought once would be effective would be limited, and they probably couldn't attack (attacking is harder than defending, and increasing casualties and disorganization remove the ability to attack first) but as they were formed it would make Lee's ability to withstand an attack slowly improve.




Burnside, Cox and the bridge

Burnside knew about McClellan's plan the previous day, and his corps had not marched particularly far compared to other formations which were also at South Mountain. They were undoubtedly tired after their exertions of the 13th/14th, but counting the 15th and 16th the corps was effectively given two days to (1) recover, (2) march via Appletown to Rohrersville and (3) march to the Lower Bridge.
Neither the march on the 15th (Fox's Gap to Appletown) nor the march on the 16th (Appletown to Rohreresville and then to the Lower Bridge) should have been a great exertion.

Despite this, Burnside started the 17th with only one division in position at the Lower Bridge, and then ordered that division away to find a ford (they then got lost). The division at the Lower Bridge had not been replaced by 9AM, after more than three hours of workable light.

I believe it is not an exaggeration to say that it would have been completely within the capability of Burnside's available assets on the 17th for him to breakfast his troops around 6AM, start them moving before 7AM (per the order which Cox reported), and have two divisions at the Lower Bridge with a third flung out to the west (to find a ford) and artillery ready to come onto the heights over the ford either by 8AM (which is when McClellan's first attack order was sent) or before 9AM (before McClellan's second attack order was sent). Under these circumstances Burnside would gain control of the bridge and be able to pass his troops over it between three and four hours earlier than he did historically (since it took ~30 minutes from the start of the bombardment to create conditions allowing 9th Corps to gain the bridge, meaning that the bridge could be captured by between 8:30 and 9:30 instead of not until 12:30).


The extent to which Burnside or Cox was responsible for the delay is debatable, but it seems to me that both bear some of the responsibility. Neither of them was ignorant of McClellan's intent; it may perhaps be indicative that it's about when Reno dies and is replaced by Cox as acting CC that 9th Corps slows right down, but either Burnside or Cox being capable of reasonable celerity would have sufficed.


A separate question is whether there is anything McClellan could possibly have done about it. There are normally four ways to deal with a problematic subordinate:

1) Fire him.
2) Leave him in position, but have a superior officer take command over him.
3) Go and take direct command of that part of the battlefield, effectively being the superior officer taking command over him.
4) Arrest him (for violation of the articles of war).

Burnside, however, is in the extremely awkward position of being a very senior commander with a direct appointment from Lincoln to command 9th Corps.
The direct appointment means that option (1) is not available - McClellan is explicitly not allowed to fire Burnside for incompetence, as per Lincoln's communications with him in May.
The seniority means McClellan cannnot have a superior officer take command over him (option 2), because there are no senior officers in the entire Army of the Potomac. The only men senior to Burnside in the combined AoP/AoV at the end of August were McClellan, Banks, McDowell and Pope, and of those men McDowell and Pope have been relieved (for their own incompetence, effectively, so not an improvement anyway) and Banks is commanding the Washington defences.
Option (3) is plausible, in that it doesn't actually violate the law, but the critical period here is from 8AM onwards - the period of the crisis on the Union right and the great majority of the actual fighting at the battle of Antietam, plus the commitment of Richardson, Smith and Slocum's divisions to the Union right. If we assume that McClellan could not reasonably know Burnside is causing trouble until around 9AM, then this means that it is this period when you effectively need three McClellans at once - one on the right sorting things out, one in the middle coordinating, and one on the left standing over Burnside doing his job for him.
This is not a feasible way to argue that a commander should deal with a problematic corps commander, especially when he has six on the field (1st 2nd 5th 6th 9th 12th) and has reasons to be worried about ALL of them except Porter (Hooker 1st and Mansfield 12th are new to corps command and indeed both cause problems of some sort even before they get themselves shot; Sumner 2nd hadn't been in the right place that morning; Franklin 6th had retreated without orders at Glendale and abandoned his command during the period leading up to Second Bull Run, and McClellan may have considerd his conduct in going to the relief of Harpers Ferry to be subpar; Burnside 9th had already been causing problems just the previous day.)
Finally there is option (4), and for this you need Burnside to actually violate an article of war. In context this means refusal to obey orders (a potential capital charge, so extremely serious), and Burnside was not actually refusing to obey orders - he was just obeying them slowly and without competence (he was moving to the bridge... slowly... he was attacking... slowly... he attacked immediately... with one regiment...)
McClellan's fourth order (around midday) is effectively an ultimatum, and Key would have arrested Burnside and put Morell in charge of 9th Corps if Burnside had not taken the bridge almost immediately (unless it turned out to be actively impossible).

You can argue that McClellan should have done this an hour or two earlier, but McClellan is extremely busy at least from 9AM to 10:30, and probably until past 11AM as Slocum is brought into position. At best you can gain maybe an hour if Burnside is spurred to order the taking the bridge immediately (at all hazards) on getting the ultimatum order, but much of the delay was already "baked in" by that point since the actual troops near enough to attack were in a state of near-mutiny. Meanwhile if Burnside had been replaced instantly by Morell at 10:30 (unfeasibly fast) then Morell still has to deal with the problems Burnside has created.




The fact that Burnside or Cox screws up enough after that that they aren't ready for AP Hill's arrival even after over an hour's warning is perhaps indicative.





The use of McClellan's remaining troops


As of about 1PM and until 4PM, McClellan is aware that Burnside has taken the bridge, and thus has reason to believe that his plan for the battle is going off (albeit belated). His primary question at this point is when to send in the troops he has which are still capable of close engagement (aside from 9th Corps, which he committed to the left yesterday and has been trying to get to attack for hours).

Those consist of:

1st Corps - one brigade has been detached as right flank guard and is still fresh.

6th Corps - five brigades of 6th Corps are still ready to go. (Irwin's brigade suffered casualties.)

These six brigades form the portion of the army's right which can advance. There are some additional troops who may have recovered enough that they can conform to an advance, but if the fighting falls on them they will not be able to contribute effectively.

Much of Sykes - some of Sykes' small division has been skirmishing but it has not been in close action, and it could all at least conform to an advance. They form the army's centre.

Morell - Morell's three brigades form McClellan's only true remaining reserve. They can be sent in in the north, in the centre, or conceivably in the south.


This effectively means that McClellan can send in a single large (corps-scale) attack, and that will be it for his capability to attack other than at the Lower Bridge. There are questions around timing and around the risk/reward to be considered (For example, if McClellan commits to an attack in the north too early, then the fighting and threat there will have been resolved by the time Burnside moves in; if McClellan exhausts his whole force in the north and Lee still has fresh brigades, the counterattack Lee was developing in the morning can happen in the afternoon instead).

It seems that McClellan's plans may at first have involved a movement in the centre, with Sykes and Morell conforming with Burnside (since the time involved for Morell to march over to the right would be significant) but around 3PM there's an argument between Franklin and Sumner over whether to attack again on the right.
Sumner (McClellan's most habitually aggressive corps commander) is actually against attacking on the grounds that to attack would risk the army, and the more stereotypically cautious Franklin is in favour (on the grounds that they can avoid the tactical errors which afflicted the previous attacks), and McClellan sides with Franklin. At this point there is basically a line plus two spare brigades formed into a column (Newton and Torbert) which were "aimed at" the Dunker Bridge.
He sends for two brigades of Morell (this may have been to keep open the option of at least some movement in the centre to conform with Burnside, or to retain at least a minimal reserve in case of an enemy attempt to break through his centre) and they march from Porterstown to the Upper Bridge.

While they are en route, AP Hill hits 9th Corps. That AP Hill's 5 brigades force the not-entirely-fresh 8 brigades of 9th Corps to retreat is somewhere between expected and good performance on AP Hill's part, but Cox orders a retreat for the whole force after the left flank is hit.

McClellan recalls Morell's two brigades to the centre, and Burnside is asking for reinforcements when McClellan returns to army HQ. Burnside gets the little two-regiment brigade of Warren, and the last battery of the artillery reserve (G/4th US), and then at 1815 with Morell back in the centre McClellan orders Burnside to counterattack and he'll have 5th Corps conform to them.
Burnside replies that he can't even hold the bridge without reinforcement.
McClellan then loans Morell's division to Burnside to help hold the bridge, on condition that they have to be given back for the planned attack the next day.



Summary of the main day of fighting at Antietam and what it means for McClellan's command

McClellan's plan on the 17th was simple enough that it could be reasonably executed, was not strongly timing dependent (i.e. it did not rely on components coordinating more precisely than was feasible) and gave each corps involved a manageable task. It was flexible enough to allow for what Lee decided to do in response, and the choice between speed and mass was feasible.
It was also a highly aggressive plan, which included an attempt to cut off Lee's army from the Potomac, and McClellan committed a very large portion of his force to attacks. The attack in the north had by 8AM included 1st Corps, 12th Corps and two divisions of 2nd Corps, totalling 89.6 regiments of all arms, while in the south 9th Corps had a further 31 regiments of all arms on the attack, as against 23.1 regiments of all arms on the field by that point which had not been actively sent in on the attack (counting none of Sykes as doing so). This equals 84% of regiments on the field (exclusive of formed cavalry) committed to attack before 8AM; once reinforcements arrive about 75% of McClellan's army actually goes in on the attack, and McClellan was quite willing to make preparations for most of the remainder to go in as well.


There were several flaws in the execution, but ultimately all of these were recoverable except for the hours of delay 9th Corps was involved in - something for which there is no feasible remedy that would not have potentially major negative knock-on effects elsewhere in the battle.


With this in mind, what the fighting on the 17th actually did was to inflict extremely heavy casualties on Lee's army on top of the manoeuvre benefits.

It I think says something that the Lost Cause arguments to explain the outcome of the battle - that Lee was actually outnumbered more than 2:1 - just make him sound incredibly foolish for not retreating south of the Potomac on the night of the 16th (something he absolutely could have done).
It's also worth considering WHY Lee did not retreat in such a way, and I think it is feasible that McClellan successfully concealed at least part of the threat that his movements posed. This may have been aided by Lee's ease at defeating Pope and his position as having been significantly reinforced since that date; Lee may also have clung to the idea of being able to continue the invasion of Pennsylvania. (It is not clear for example whether Lee was intending to attack and try to knock Hooker's 1st Corps out the way once McLaws and Anderson arrived.)



Aftermath


On the 18th, there was no major fighting. This appears to have been partly the result of neither side having sufficient assets for major offensive combat, though it is also possible on Lee's part that he had decided to move by the flank (from Sharpsburg to Williamsport) and was simply waiting until the last of his wagons had crossed the Potomac before doing so.



McClellan's prospects for an attack on the 18th

As of the 18th, many of McClellan's previously shattered formations were rebuilding, though they were not yet up to full offensive combat; it is hard to find an example anywhere in the war of the same Union troops attacking for a second time the day after they had been repulsed the first time, though a "day off" followed by a second combat seems much more manageable.

With this in mind, the available troops McClellan had for an attack were surprisingly scant. Of the troops which he had available on the field which had not already been used, there were:

Fresh troops on the right at daybreak: (1 bde 1st, 5 bdes 6th) about 27 regiments (6th Corps) +4 (Hoffman) but -5 (Irwin) so 26 regiments.

Fresh troops in the centre at daybreak: Sykes (regulars only) so about 7 regiments.

Fresh troops on the left at daybreak: Morell's division (20.5) and Warren's brigade (2) so 22.5 regiments. These are units which in Morell's case Burnside is refusing to give back (he's pulled 9th Corps back east of the bridge and put Morell into position to the west of it).

Couch's division (15.4 regiments, though may have left a little strength at the Maryland Heights?) arrives on the mid-morning of the 18th. These are theoretically available to send anywhere.

Finally Humphreys' green division with 8.2 regiments arrives later in the day (it is not clear when - McClellan's report says they weren't available until late in the day, while Humphreys claims to have made a 23 mile forced march overnight and reached McClellan's HQ by 7AM - it seems likely that the difference is the filtering in of stragglers). These are all new troops, so they should be stronger than average according to the raw regiment count, but they're also very tired and not really fit for combat on the 18th. McClellan sends them south to swap them for Morell as Morell's division is fit for combat and Humphreys can at least defend the bridge, but Burnside refuses to send Humphreys back.


If McClellan felt it was critical to attack on the 18th, he could have mounted one significant move. To do this may have meant arresting Burnside to get him to relinquish Morell (or, given Burnside's feelings of great danger on the southern flank, to get him to attack) but the best case is:

26 regiments in the north.
Couch and Morell's divisions in the north (Humphreys in the south) so another 36 regiments in the north. Total 62.

This is a fairly sizeable force, but it's everything McClellan has left - basically a Pickett's Charge - and would have faced notable difficulties in coordinating the movement of troops to the right flank. Assuming that McClellan is willing to make the order to give up Morell peremptory and relieve Burnside if he does not comply, however, such an attack could have been launched. (It would be lacking artillery support as McClellan's artillery was mostly out of long range ammunition, and a resupply would not arrive until late in the afternoon.)

It would be hitting the strongest part of the Confederate line. There were McLaws' and Walker's divisions, plus the brigades of Early and Armistead, and behind them were the various brigades of Jackson etc. from the previous day's fighting who were rallying. At least one contemporary map shows the Dunker Church plateau as being protected by a line of "breastworks" along the eastern edge of the woods (which may represent actual breastworks or simply the defensive strength of the position in the woodline), so it would be a difficult target, and even if successful the attack would merely do a bit more damage - it does not offer the prospect of the Union destroying the Confederate army by cutting in behind them, and the Confederate force still has an intact center and right (and the assembly of this force would remove the Union threat to those sectors, allowing them to be stripped). In other words, to actually destroy Lee's army then this attack would have to first overcome the Dunker Church defences and then wheel left into the whole of Lee's remaining force.

It is possible that this would have had a useful effect, but it is by no means certain, and the risk is not necessarily worth the gain. As things stood at Antietam on the 18th, McClellan's army could fulfil the lesser campaign goal (end the invasion of the North) simply by not being defeated, and to attack recklessly would risk that.

There are alternatives. One of them would be to order Couch's division to the bridge at the very mouth of the Antietam itself, and thus attempt to get between Lee and the Potomac fords, but this would effectively mean that Couch was making an independent movement (which could be very risky to Couch, though not necessarily risk the whole army) and another would be to have Couch reinforce Morell west of the Lower Bridge and launch an attack there. This final option would essentially be a 9th-Corps-scale attack again, but without Morell's division to conform to its right flank.




Overnight on the 18th-19th, Lee withdrew his army south of the ford. Troops had been observed moving north over the ford on the 18th, so it is not quite clear whether this was a sudden decision or one he had planned after the fighting of the 17th, but one thing that is clear is that if he had not withdrawn McClellan would have attacked him; McClellan moved at dawn with his whole force and pursued Lee to the water's edge, fighting a small action near the Potomac itself.


The next few days saw what was effectively a (short) manoeuvre campaign, and I will address it separately.
 

Saphroneth

Major
Joined
Feb 18, 2017
The end of the Maryland Campaign



On the morning of the 19th, much of Lee's army was still close to the Potomac (marching to Martinsburg), while there were reports that Lee was moving to Williamsport further north to cross there. In the afternoon McClellan sent Couch's division (which was one of his comparatively fresh units) marching north to Wiliamsport to block any attempted Confederate re-entry into Maryland, while 5th Corps was sent to cross the Potomac at the Shepherdstown fords.

19th_day.jpg


It's important to point out here that if Lee had retained his whole force at Shepherdstown, any kind of crossing attempt by McClellan there would have been completely pointless. The defiling effect of a river crossing makes the crossing of a defended river at a single point difficult - notice how much a brigade of infantry and a battery of artillery caused in the capture of the Lower Bridge.
This means that Lee was not simply thinking in terms of force preservation when he moved to Martinsburg, but was probably wanting to keep open the option of invading the north again via Williamsport.
Wht actually happens is that 5th Corps successfully attacks the Confederate rearguard on the 19th, and is in the process of crossing the fords on the 20th when (most of) the combination of Ewell's division and AP Hill's division counterattack and force the 5th Corps back across the river.
If the whole of the 5th Corps had been crossed by that time (something which would require several hours of daylight - a night retreat crossing of a controlled ford is doable, a night crossing into secured territory is doable, a night attack over a river in the face of the enemy is very dangerous), it would have been about 45 Confederate regiments against 38 Union ones, which sounds like quite a fair fight; however this is where the problems with the new regiments really show themselves. The 118th Pennsylvania turns out to be totally combat ineffective as their muskets are faulty (and have never been loaded or test fired); while the rest of the new regiments may not be quite so incapable, it's a bit of a problem.
Lee could also have sent more troops than he did (what he sent was roughly on par with a fairly strong Confederate corps). Either he felt that those brigades were sufficient for the task or he wanted as many brigades as possible at Martinsburg (presumably for his planned re-invasion of the North).

Shepherdstown isn't the only thing McClellan is doing over this period however. 6th Corps moves to reinforce Couch at Williamsport, blocking any planned movement by Lee, and at the same time 12th Corps marches down to reoccupy the heights over Harpers Ferry. (They are followed by 1st and 2nd Corps on the 22nd, and 9th Corps with most of the cavalry on the 23rd)

Movements on the 20th
20th.jpg

At this point both sides contest the Shepherdstown and Williamsport fords, but McClellan has control of the crossing point at Harpers Ferry. He has issues with supplying his force (supply is coming from Hagerstown but it's not ideal, and there are problems with supply over the Monocacy) and he plans to cross to attack Winchester.


Situation up to the 26th
up_to_26th.jpg




On the 22nd, Sumner is ordered to put a pontoon bridge over the Potomac, and McClellan requisitions the money to repair the rail bridge there.

On the 23rd Halleck asks what McClellan is planning. The same day, Sumner's pontoon bridge is established, but that night a storm hits the area and the resulting freshet (sudden rush of fast water) wrecks the bridge before it can be used.

On the 24th McClellan replies to Halleck that he is going to cross the Potomac into the Shenandoah and attack Winchester - cutting Lee off from his line of supply in the upper Valley. He also argues in favour of a permanent wagon bridge, though that OR the rail bridge would suffice to advance in force.

McClellan's operational thinking here is to exploit the rising Potomac. He already wanted the Shenandoah bridge repaired anyway (it's something that has to be done to best exert control over the upper Potomac) but if the storm is making the Potomac unfordable then control over the Harpers Ferry bridge means that McClellan can enter the Shenandoah without worrying about Lee crossing the Potomac to the north. In light of this on the 25th he asks for 11th Corps (which Halleck had suggested he was going to get) to be sent to Knoxville a few miles east of Harpers Ferry.

McClellan's plan
plan_27th.jpg


Also on the 25th, Lee writes to Jefferson Davis that he presumes that McClellan will be crossing the Potomac by bridge at Harpers Ferry and advance into the Valley. In the same message Lee says that his army has been so badly damaged not merely in numbers but in morale that he can't risk an offensive movement.

On the 26th, Halleck sends two telegrams.
One (sent 1:40 PM) says that before more troops were sent to McClellan "we ought to have a full understanding in regard to your future operations" and that McClellan's plan to cross the Potomac "at or above Harpers Ferry" would expose Washington. He further says (next sentence, same paragraph) that the Confederates are repairing bridges on the Rapidan and Rappahannock, and are planning to "throw a force on Washington" if it's not properly protected.
Halleck asks McClellan to move his army "so as to cover Washington, by keeping between it and the enemy".

Halleck's argument in this telegram makes no sense unless the force he is worried about is on the Rappahannock (i.e. around Fredericksburg or Culpeper) rather than being Lee's actual army. This is reinforced by the second telegram.

The second telegram has no time stamp, and in it Halleck says:
- that the War Department will not authorize the expenditure of large sums of money unless they are "informed more definitively of his plans", and that he does not know McClellan's plans. (Halleck presumably does not mean that McClellan has not told them what his plans are, because Halleck in the first telegram made it obvious that he DOES know what McClellan's plans are - he repeats them. Halleck must mean something else.)
Halleck then says that he had hoped that "instead of crossing at Harpers Ferry... you would be able to cross lower down the Potomac, so as to cover Washington by your line of operations, and thus avoid the necessity of keeping a large force here".
Halleck also repeats the point about a worry that the Confederates will be threatening Washington from the direction of Manassas.
He admits that McClellan's plan to cross at Harpers Ferry will relieve the danger to Washington while the Confederate army is at Martinsburg, but asks "will it if his main force falls back on Winchester?"
It's not clear what Halleck means by that question - he may be picturing the Confederates falling back to Winchester, then moving east of the Blue Ridge to threaten Washington that way, but the fact that he asks McClellan to "cover Washington" by crossing the Potomac east of Harpers Ferry, and the mention of the danger to Manassas, makes it indisputable to me that Halleck is worried chiefly about a whole other Confederate army on the Rappahannock.


I should point out here that as of the 20th of September the garrisons of Washington amounted to more than 70,000 men PFD (71,200). On the 30th of September (the next report) the number is slightly higher - about 73,600 PFD.
Meanwhile, the Confederate force on the Rappahannock which Halleck is worried about consists, to the best of my knowledge, of the 61st Virginia infantry (acting in the area of Bristoe Station to Catletts Station to recover burned railroad cars etc. and part of which fought a skirmish on the 29th involving a couple of hundred men on each side) and the 15th Virginia cavalry at Fredericksburg.

Absolutely nothing should have prevented plenty of reinforcements being sent to McClellan. (New regiments did arrive with McClellan over this period, and the defences of Washington continued to trend upwards.)


The upshot of this is that Halleck wants there to be "a full understanding" of McClellan's plans, by which he means that McClellan's current plans communicated to him will not do, and furthermore that Halleck (or "the War Department" which may mean Stanton) will not approve the resources McClellan needs to advance.

This is effectively the final end of the Maryland/Antietam campaign, though the argument that resulted continued with varying degrees of celerity for another month.




The operational situation that prevailed in this period is one where McClellan would have had definite difficulties in making an attack into the Shenandoah. If McClellan had managed to successfully cross at Shepherdstown then it is possible that he could have brought Lee to battle in the next couple of days, but it is more likely that either:
- Lee retreats south to Winchester
or
- McClellan bringing his troops and trains across the Shepherdstown fords take the next few days

Either way, once the storm of the night of the 23rd arrives McClellan gets cut off from his supply line, and he would be for the next several days until the Potomac subsides again.

It is possible that McClellan could have crossed 6th Corps specifically (as they have the shortest route to a rail supply point, that being Hagerstown, and were the strongest corps) but this would tend to push Lee down the Valley towards Winchester and that is something McClellan does not necessarily want to happen if he has a choice - he would rather cut in behind them. If the Potomac did then rise it would mean that 6th Corps was cut off from supply until the river fell again, and without a bridge at Harpers Ferry Lee could concentrate his entire effort on 6th Corps if he felt it would produce a good result.

Lee's position at the banks of the Opequon in this period is a little harder to understand, unless he felt that he would have a reasonable amount of warning of any resumption of the offensive by McClellan. Lee certainly felt that McClellan building bridges at Harpers Ferry would be a danger to him and pulled back half his army to Winchester.

Lee's movement in response to the threat of McClellan crossing at Harpers Ferry
move_28th.jpg
 

Saphroneth

Major
Joined
Feb 18, 2017
What Lincoln thought?

In the diary of Orville H. Browning, in a meeting with Lincoln on the 29th November it is reported that Lincoln said:
- he'd sent for McClellan to defend Washington, and had "brought order out of chaos", and that "for such work McClellan had great talents"
- that "for organizing, disciplining and preparing an army for the field and handling it in the field he was superior to any of our generals"
- that Lincoln had sent for Burnside to command the army when Lee crossed into Maryland, but Burnside declined as the task was too great.
- that McClellan fought South Mountain and Antietam "as well as any general could have fought them".

The only complaint Lincoln has about McClellan here is that he's too slow. Lincoln's picture of McClellan is that he's the best organizational general, the best training general, and the best field commander that the Union has - his only disadvantage is that he's too slow.

One of the things which Lincoln mentions here to show how McClellan is too slow is that he let Lee get back across the Potomac after Antietam "without the loss of a man", which is a pretty incredible thing to say given the actual events of Antietam, and then Lincoln says that McClellan "would not follow" while McClellan did in fact pursue - he just got stop-punched, and then effectively prevented from doing so.

The rest of what Lincoln says in this section relates to a later period than we've already covered. It is interesting though that in the same conversation Lincoln had nothing but praise for Pope's manoeuvres...
 

Saphroneth

Major
Joined
Feb 18, 2017
For the period from late September until McClellan commences the Loudoun Valley campaign there are several interlocking factors at work.



Training the army.


The first thing which I should stress is that, while McClellan was not advancing, he was not spending the time idly either. In the Maryland Campaign and at Antietam the Union army had suffered from how it had not been properly articulted, and from how green the troops were, and surviving testimony indicates that McClellan took the opportunity to train his army heavily - indeed, one complaint from contemporary soldiers (13th MA) was that the army was being drilled hard enough that it barely had time to eat.

One of the things McClellan is often praised for is for his ability to build the Army of the Potomac, and while part of that was the long months of drill over the first autumn and winter this second period (from around September 20 to the end of October) was also a period of building the army - in particular integrating the new regiments into the force and ensuring that the brigade, division and (to some extent) corps commanders know what they're supposed to be doing.

A good example of the effect of this is the ability of the army to march during the subsequent Loudoun Valley campaign. Some individual corps move great distances and do so without issue - two divisions of the 9th Corps march 16 miles on the 5th November and then 25 miles on the 6th November, while even the two divisions* unable to keep up with the march on the 6th still managed about 20 miles on that date. This is an impressive achievement by any measure.

* at this time Whipple's division was attached to 9th Corps; it would go on to be incorporated into 3rd Corps.



The operational situation.

two_options.jpg

For much of this period, the situation of the armies was fundamentally as presented in the post above except in that the 1st Corps was moved away from Harpers Ferry during part of this period. The Army of the Potomac increased over time (going from a bit under 100,000 Union PFD on 30 September to a bit under 130,000 Union PFD on 20 October), to a greater extent than Lee's army did (which recovered some casualties, but had a much smaller percentage increase from all sources over the same period).


Under this situation, the most preferable situation is for the Union to be able to advance over the (bridged) Potomac at Harpers Ferry, and at Williamsport and Shepherdstown with the two independent corps there. This presents too many threats for Lee to deal with one at a time (since the large force at Harpers Ferry could cut him off in the upper Valley unless he pulled back, while since the 5th and 6th Corps have to be there anyway to block his re-entry into Maryland they can advance so as to get them into the fight) and offers Lee the choice between pulling south (of Winchester) or being potentially cut off.

This would not in and of itself guarantee a Confederate defeat, as a defeat can only happen in this situation if Lee risks one. It would however clear the upper Valley of Confederate forces, and remove the need to keep large forces along the upper Potomac to prevent Lee's invasion of the north.


The alternative to clearing the upper Valley is to not clear the upper Valley, and go after Richmond directly. There are two possible approaches here, one being to make a naval movement and the other to make a movement over land.

The naval movement is actually dubious (though not necessarily a non starter) under the conditions which currently prevail, because the whole Confederate field army being in the upper Shenandoah means that a large force is required to keep the North safe - both along the line of the upper Potomac and keeping Washington itself secure. This necessarily limits the size of the force that can be transferred to face Richmond directly, and of course Halleck is raising questions about keeping Washington secure.

The other possible move, and one which is brought up more than once over this period, is for McClellan to move south towards Richmond directly.

The upsides of this move relate mostly to how it would threaten the Confederate capital, and how it would be logistically quite well supported - there are railway lines reaching out from Washington at regular intervals until the line of march reaches the Rappahannock (though some of them are badly damaged).
It also has downsides, however. The first is that with half of Lee's strength concentrated at Martinsburg and the other half at Winchester the threat of a re-invasion of the North can't be ignored, and this means in turn that a large part of the strength of the Union army has to be kept along the upper Potomac; with a corps required at Shepherdstown, Sharpsburg and Harpers Ferry to prevent this, even if we assume that part of the 6th Corps could be brought along it means that the Union would be leaving between 40,000 and 60,000 PFD along the upper Potomac - reducing the strength of the Army of the Potomac considerably, and meaning that the moving section of the Army of the Potomac could actually be outnumbered by Lee's army.
10th October strengths, Aggregate Present:
Main Army of the Potomac 129,000 all told
Half of 6th Corps (Williamsburg) 14,500
5th Corps (Sharpsburg) 21,500
12th Corps (Harpers Ferry) 17,500
Total 53,500 AP
Remaining army for the offensive 75,500 AP
Lee's full strength, same date: 78,000 AP

If McClellan started south with the indicated column (1st, 9th, 2nd, half 6th) then it would be possible for Lee to fight a battle at a local advantage.

While this is the main problem, it is also worth pointing out that an advantage it offers is lessor than what might be argued. It had been argued (by Lincoln specifically) that the route McClellan had to reach Richmond was shorter than the route Lee had to reach Richmond, but this falls apart on two major problems.

The first is that if both armies start moving south at the same time, then the primary issue is a race to Culpeper. From Lee's southern corps at Winchester to Culpeper is a route of almost exactly 60 miles (via Middletown and the Front Royal Gap) or 56 miles going directly from Winchester to Front Royal to Culpeper, which is a move which Lee can largely make in column of march and down pike roads. For McClellan on the other hand the route is longer (70 miles from Harpers Ferry to Culpeper) and this path largely does NOT involve pike road movements, in addition to this "shortest route" missing out on at least two of the railway lines that could be used for supply.

The second is that Lee's route to Culpeper involves only one major river crossing, the Shenandoah, and this can be crossed at the fords just above the confluence of the North and South Forks (at Front Royal) or if bridges are mandatory then the route can detour to Strasburg and have a route of a little under 70 miles which crosses all significant rivers at proper permanent bridges.
McClellan's route to Culpeper, meanwhile, involves crossing both the Potomac and the Shenandoah (for the shortest route), and over bridges which he hasn't yet been permitted to start building.
The time delay involved in building these bridges would make it a longer march (in duration terms) even before factoring in that McClellan would be advancing to contact and consequently would not be able to conduct a simple route-march through known friendly territory - the route passes close to the Blue Ridge gaps, and Lee could easily attack the column in the flank - and so arrangements would have to be made to allow for this possibility, which would lengthen the time and distance the route would involve.

If Lee ignores the possibility of blocking McClellan at Culpeper and decides to just go straight for the defences of Richmond, he would have a march from Winchester of a bit less than 100 miles to Staunton, where he would be able to rail directly to Richmond; alternatively he could march via Swift Run Gap (170 miles). Both of these routes involve no significant river crossings.
McClellan's route here would actually be shorter (~155 miles going via Culpeper, as opposed to ~170 for the Swift Run Gap route) but woud involve a much more significant amount of river crossing. This would quickly erode away the supposed advantage in shorter route length, even before considering that McClellan's route here is not logistically viable. To pick up supply the route would need to hook east to Fredericksburg at some point after crossing the Rapidan, which would increase the length of the route to about 180 miles.

Conversely if McClellan takes the shortest route all the way to Richmond, McClellan's route is

This does not mean the approach is completely non viable. Instead, it means that (1) the need to garrison the upper Potomac must be addressed, even if only in a viable plan to pull away from the upper Potomac only after Lee has moved south, and (2) that the idea of beating Lee in a "race to Richmond" is not practical.



Supply problems


For much of the period after Antietam there were serious supply deficiencies affecting the Army of the Potomac. This particular topic has been looked at in considerable detail by Stephen R. Stotelmyer, and the following is drawn largely from that work.

Key players:
Ingalls (Army of the Potomac supply chief)
Meigs (chief quartermaster in Washington)
Halleck (General in chief)
Stanton (Secretary of War)


The army had set out from Washington in such a hurry that a lot of the force had not had time to properly procure supplies. The lack of wagons meant some units left their backpacks in Washington and never saw them again.

This means that the army is going to need at least some amount of rebuilding; there are plenty of testimonies of the shortage of equipment, and there were also testimonies about food shortages. Indeed, a food riot took place during Lincoln's visit and within sight of his carriage.

27th IN of 12th Corps notes deficiencies, with supplies arriving a few days after the 20th September and "very slowly and in small quantities".
The chief of artillery to 1st Corps noted a serious lack of supplies (equipment in this case) and that they'd been lacking it for months.




September 21: Ingalls asks for the main depot to be set up at Harpers Ferry; McClellan requests the War Department repair the sabotaged Baltimore and Ohio.
September 22: Meigs argues that there is concern about raiding over the Potomac interrupting the supply line from Washington via Frederick and along the banks of the Potomac from Point of Rocks.
McClellan insists on the repair of the canal.
McClellan also requests repair of the bridges over the Potomac at Harpers Ferry.

September 25: the bridge is ready to be repaired.
September 26: Halleck shuts down the idea of repairing the bridge.

September 30: Ingalls informs Meigs of significant supply problems (railroads not forwarding supplies, and AoP quartermasters having to do the jobs which should have been handled by QMG personnel)


October 1 onwards: Lincoln's visit.

October 2: Meigs forwards Ingalls' telegram to the president of the Baltimore and Ohio railroad, but takes no other action.
Meigs also gets a telegram from the master of transportation of the B&O asking for a quartermaster to be stationed at Sandy Hook, and sends it on to Ingalls saying that the QMG can't supply quartermasters everywhere they might be necessary.

October 2: food riot in the 9th NY. Lincoln saw it, but said nothing.

October 3: Lincoln reviews the 1st Corps. Many 1st Corps officers mention that the army had ragged and worn clothes.

Same day, the New York Tribune claims that the condition of the troops is "good".

October 7: McClellan mentions the problem with supplies, saying it'll be at least three days before 1st/5th/6th Corps will be able to move.

October 10: Ingalls sends a telegram to the depot QM at Washington asking where the clothing that was meant to be going to Hagerstown is, and to the QM at Hagerstown to ask him to issue it immediately when it arrives.
On the same date, Haupt tells Ingalls that the delays are because supplies were going to "Harrisburg" instead of "Hagerstown".


Octobr 11: McClellan tells Halleck that requisitioned supplies are arriving much more slowly than they should be, and that corps commanders have been sending wagons to pick up material which was due to arrive but which is not. This includes a lack of shoes.

The depot QM at Washington sends Ingalls a detailed statement of times which supplies left Washington for Hagerstown.






October 13: McClellan complains about the supply of horses for his cavalry.

October 13: Meigs makes a report listing the number of horses issued to "the army of General McClellan, including that part of it in front of Washington".

October 14: Meigs reports to Stanton the number of horses supplied to "the army under General McClellan, including that in front of Washington"

October 14: some shoes and clothing arrives at Hagerstown. (McClellan telegram to Halleck)
Hallck writes to McClellan that all requisitions had been filled.

October 15: Not as much has arrived at Hagerstown as called for (telegram from McClellan's chief of staff to Ingalls)

October 16: 1st Corps finds no shoes at Hagerstown,leaving them with over 5,000 shoes deficit



October 18: McClellan states that Meigs may have ordered the articles to be forwarded, but they were not reaching the depots.
Ingalls gives this date as the date which clothing requisitions made on the 7th October for 1st/5th/6th Corps arrived at Hagerstown.

October 21: Lincoln's investigator (Col. Scott, assistant secretary of war) reports to Lincoln that the supplies for McClellan's army had not been forwarded, and that they had been sitting in sidings or in the forts at Washington.
McClellan writes Halleck to the effect that shoes, winter clothing, and horses for the combat arms are absolutely essential for an advance.

October 22: Meigs tells McClellan that a "special wagon train" had been dispatched, while continuing to claim all requisitions had been fulfilled.

October 23: George Meade (interim 1st Corps commander at this point) tells his son that he sent a telegram on the 7th requisitioning 3,000 pairs of shoes and that no pairs have been recieved yet.

October 24: Meigs states to Halleck that there cannot have been any lack of supplies.

October 25: Meigs reports the number of shoes that had arrived with McClellan's army, giving the numbers then in store and the numbers in store on the 21st.
Stanton noted that McClellan had "publicly alleged" that Meigs had not forwarded supplies.

October 26: Alpheus Williams (12th Corps commander) tells his daughter that he'd sent requisition upon requisition but nothing had arrived.



October 27: Stanton launches an official inquiry, directing Halleck to report whether there was any supply deficiency that would have prevented McClellan advancing.

October 28: Halleck's reply states that McClellan's requisitions had all been "immediately filled" except on one occasion, and that there had been no neglect or delay in issuing supplies. Some delays had taken place, but Halleck claimed that the problems were resolved more quickly than would be normally expected.




McClellan's report includes a large table showing the arrival of various categories of equipment. Some categories of equipment (sack coats and shelter tents) arrived in significant quantities before October 6, but in almost every other category much of the equipment arrived much later. (In boots for example, 4,200 arrived from September 1 to October 6, 6,000 from October 6 to October 15, 3,600 from October 15 to 25, and 20,000 from October 25 to 31.)
This is attributed by Ingalls to have been due to slow movement over the roads (which means railroads, a common shortening in the language of the time).

McClellan also notes that, of the 1st, 5th and 6th Corps:
1st Corps had to delay for a day when crossing the Potomac to resupply (on the 27th)
5th Corps only finished resupplying actually at Harpers Ferry (on the 30th)
6th Corps didn't finish resupply until after crossing the Potomac (2nd November).


So to summarize this, very large amounts of necessary supplies were requisitioned by the Army of the Potomac and were "techncially" delivered (but in fact delivered to the part of the army around Washington, instead of the field army), for weeks until the "problem" was discovered. Halleck amd Meigs were either complicit in this or, at minimum, insufficiently competent to discover the failing; Stanton later claimed that there was no supply crisis at all, which is false. (Interestingly at the same time he claimed that he hadn't colluded with Secretary Chase against McClellan, and the petition to rmeove McClellan alone indicates that that latter claim is false).

During this period, newspapers were talking about how there was no supply crisis.
What this seems like is either:
1) Incompetence in Washington, combined with "politics as usual" in fabricating stories about how there was no supply crisis.
2) Active efforts to "misdirect" the supplies for McClellan's army by only technically fulfilling the requisitions, a possibility suggested by the careful phrasing "McClellan's army, including the portions in front of Washington" on more than one occasion (particularly when talking about the supply of horses).






Permissions

October 1 - Halleck asks why McClellan hasn't already crossed the river without bothering with needing a bridge, and says that the delay involved from building permanent bridges would be too long (which is an incredibly short-sighted way of dealing with a time consuming problem - to not start the task on the grounds it would take too long). He also tells McClellan to consult with Lincoln, who will arrive later that day.


Lincoln's visit sees McClellan writing to his wife part way through the visit that he thinks Lincoln's purpose is to push McClellan into a premature advance into Virginia.

October 4 (last day of Lincoln's visit) is the discussion with McClellan.

Lincoln later said (two weeks later) he admonished McClellan's overcautiousness.
McClellan said (to his wife) that Lincoln told him he was convinced that "I was the best general in the country" (which is in keeping with the diary note). McClellan also came away with a feeling that Lincoln felt kindly towards him.

Later (1887, McClellan's Own Story, in the section after the manuscript runs out and thus presumably reconstructed from notes) McClellan (or "McClellan" given that some of the Own Story was assembled after McClellan's death) wrote that the only fault Lincoln could find was that "I was perhaps too prone to be sure that everything was ready before acting". He also wrote that Lincoln wished McClellan to continue his preparations for a new campaign and not to move until fully ready - and when ready, to take his own choice on what to do.

Allen Rice related that McClellan said that Lincoln intended to give him time for preparation, and that McClellan's main worry was over politics in Washington which Lincoln would not be able to resist.
Joseph Kennedy reported that in a subsequent discussion between him and Lincoln much the same themes were in place; Lincoln was confident in McClellan, but that there were politicans in Washington who were more against McClellan than they were against the actual Rebels (and would rather see him fail than succeed). Lincoln also said in this discussion that any change in public attitude towards Lincoln would be for political reasons.


5th October: Cox's division is removed from 9th Corps.

6th October: Halleck's long telegram.
- McClellan is directed to cross the Potomac and give battle to the enemy or drive them south.
- McClellan would get 30,000 reinforcements if he crossed east of Harpers Ferry and 15,000 if west.
- "The President advises the interior line, between Washington and the enemy, but does not order it."
McClellan is ordered to report when he would cross and what route he would take, and Halleck said that “It is necessary that the plan of your operations be positively determined on before orders are given for building bridges and repairing railroads.”


Halleck is basically ordering McClellan to move, while giving him a choice of which route to take. Halleck also orders McClellan to say what route he is to take, and that the plan must be "positively determined on" (i.e. Halleck has to agree with it) before McClellan is allowed to give orders to build bridges etc.

This means that McClellan has been effectively prohibited from moving unilaterally. Whichever route he takes would require a bridge to be built to cross the Potomac.


7th October:
A telegram from Halleck at 12:45 PM says that scouts report the Confederates "in force" at Mount Jackson, Sperryville and Warrenton. This seems to effectively be a false report.

McClellan replies at 1PM (to Halleck's missive of the previous day) with a telegram in which he says his plan is to enter the Shenanodah for "immediate" operations against the enemy, but that he does not plan to use it as the line of operations long term.
His reasoning is:
1) To cross the Potomac east of Harpers Ferry would let the enemy attack Maryland and Pennsylvania.
2) If McClellan moved south to the east of Harpers Ferry and then turned west into the Shenanodah, Lee could defend that river by getting to any given part of it before McClellan could reach it.
3) The Shenandoah Valley is only important in so far as the enemy are there and McClellan wants to fight them. He will either have a battle, or otherwise, he'll force the enemy to abandon the northern part of the Valley. At that point he'll rethink.

Also on the 7th, Halleck says he is "satisfied" that the enemy is falling back towards Richmond (they're not), and complains that McClellan's army has too much immobility and that this is because they're not getting enough exercise. In fact McClellan is heaily drilling his whole force.


On the 8th, Halleck orders Banks that all troops not required for the defence of Washington to be ready to immediately take the field. The same message goes to Heintzelman.
They don't actually do so.


October 12: Haupt (in charge of railroads) tells Ingalls that the bridges at Harpers Ferry can't be expected to be finished soon, so a pontoon bridge will be required.
He also tells McClellan much the same thing, specifying a wagon bridge.

On the same day, Marcy (QMG) tells John Garret (president of the Baltimore and Ohio) that the bridge at Harpers Ferry will be planked for crossing infantry but that "it will not be used for wagons, unless an extraordinary and unlooked-for emergency should arise".


October 13: it is stated that Whipple and Stoneman's divisions are to report to McClellan. (Functionally they start guarding the lower Potomac.)

October 15: Halleck complaines about the inactivity of the Army of the Potomac.

October 16: McClellan sends out recces (Hancock to Winchester and Humphreys to Martinsburg, both supported by their corps, with cavalry) to check enemy positions.

Lincoln sends a letter where he complains to McClellan about being over-cautious.
We should note that at this point Halleck had ordered McClellan to provide his plan for approval, and McClellan had done so, and Halleck had not approved or rejected it. McClellan has effectively been in limbo up until this point.
Lincoln's first paragraph chides McClellan for over-caution, arguing that McClellan should show as little care for his supply lines as Lee did. Lee of course just nearly straggled his army to bits about a month ago.
In the second paragraph, Lincoln doesn't understand the substance of why McClellan wants a permanent bridge at Harpers Ferry. He argues that McClellan can't need the bridge to get to Winchester because Lee is supplying himself at Winchester from further away, but of course Lee has his river crossings (of the Shenandoah and the forks of that river) intact, so his supplies can run up those pike roads, and a flood wouldn't interrupt them. For McClellan meanwhile he's already suffering from supply problems even standing still because of the delays on the rail line, and if he advances halfway to Winchester and then a freshet destroys the Potomac bridge then McClellan's whole army is cut off from supply.
The third paragraph sees Lincoln arguing that if Lee and McClellan swapped places then Federal Lee would break Rebel McClellan's communications with Richmond within 24 hours (which is functionally impossible even if Rebel McClellan did nothing, it's at least fifty miles and involves a major river crossing to get to the closest point that would be achievable). Lincoln also argues that McClellan should let Lee invade Pennsylvania and then cut off Lee's communications, which is absolutely not what Lincoln insisted on when this circumstance actually arose in 1863.
The fourth to sixth paragraphs see Lincoln argue that McClellan should be able to beat Lee to Richmond because of distances. This is already incorrect (see the calculations above) but Lincoln goes further by saying that it's unmanly to say that Federal troops couldn't do it (his logic is that Federal troops should be able to march as well as Rebel ones, but he's actually giving them a harder task and expecting things to work out better).
Weirdly Lincoln also argues that the roads on the route east of the Blue Ridge are as good as the roads in the Valley, and they're simply not - the Valley has the macademized Valley Pike plus the Front Royal Pike which means almost Lee's whole journey down to (say) Culpeper is on pike roads, while McClellan if moving east of the Blue Ridge has no pike roads from Hillsborough to Warrenton if he's moving on the direct route, and not much on other routes.

Notably, Lincoln also reiterates that he has NOT given McClellan an order to go either east or west of the Blue Ridge mountains.

This letter reaches McClellan as he's departing for the field for his recce-in-force with Hancock and Humphreys. It looks like there might be a battle and an artillery duel starts; I suspect here that McClellan might well have been trying to get his preferred advance going without formally ordering it.


October 17:
McClellan sends a reply to Lincoln, saying that he adopt Lincoln's idea UNLESS there were reasons not to (which he would explain) and said he'd move as soon as his men were shod and his cavalry horses sorted out.

An engineering report notes that to defend Harpers Ferry a better permanent bridge is needed - there's a pontoon bridge but this is wholly unreliable in winter and could easily be washed away.
McClellan forwards this to Halleck on the 18th, noting that a bridge is required just to defend the place.

October 19: Halleck replies saying that building a permanent bridge where McClellan wants one is unnecessary, and says that it'd be better for McClellan to cross east of the Blue Ridge mountains. Stanton approves this on the 20th.

October 21: given the ongoing supply problems are starting to be resolved but the horse problem is still an issue, McClellan asks whether Lincoln wants him to advance at once or wait until the horse problem is resolved.

Halleck replies the same day, and says that he asked the President and that there is no change to the order of the 6th October.

Remember, the order of the 6th is that McClellan needs to send his plan and have it approved before marching, and the rest of Halleck's reply effectively reiterates this as it orders McClellan to telegraph when he'll move and what approach he should take.


McClellan's reply on the 22nd sees him agree to move east of the Blue Ridge mountains (as per his letter of the 17th, a decision McClellan probably made partly because of a combination of the river rising again and sheer frustration).
Halleck approves it after about 24 hours (a far cry from his opinion of the move into the Shenandoah, which went unapproved for over two weeks), and McClellan gets approval late on the 23rd (about half past five in the afternoon).
At this point McClellan still has to leave 5th, 6th and 12th Corps along the upper Potomac, and will only be able to move with 1st, 2nd and 9th Corps plus the divisions of Whipple and Stoneman. More troops are slated to join him en route, but he's been promised and denied reinforcements before, so functionally speaking McClellan could well end up moving with (November 10 figures) 79,800 Aggregate Present.
Lee's field return for the 10th November gives him 83,400 Aggregate Present (this does not include Pendleton's reserve artillery), so this is a risky move.


I should point out here some curious language used by Lincoln and Halleck.

Lincoln was insistent on multiple occasions that he had not ordered McClellan to take either route (either west or east of the Blue Ridge). On the 26th, meanwhile, Halleck was at pains to say that "I have advised and suggested in relation to your movements, but I have given you no orders".


The fact that when McClellan submitted a plan to move into the Shenandoah it was sat on for weeks, but a plan to move east of the Blue Ridge was accepted within a day, suggests that Halleck (and possibly Lincoln) wanted a particular route to be used without actually explicitly ordering it (and going out of their way to say they did not order it).

What it looks like is happening is that politics is being played. Both with this, and with the supply problems (which were at the very least being concealed, if not actively created) a situation is created where McClellan can be attacked in the press for untruthfulness and where people within the Administration can misrepresent him to Lincoln.





What should have been done


Halleck


For the purposes of this analysis I will assume that Halleck honestly wants McClellan to advance.

If Halleck is okay with an advance west of the Blue Ridge:

He should have replied promptly to McClellan's plan of the 7th with an approval, possibly caveated (such as to the effect that McClellan had to cross by day X).

If Halleck considers an advance east of the Blue Ridge mandatory:

He should have replied promptly to McClellan's plan of the 7th with a rejection.

Regardless:

He should have approved the construction of a permanent bridge at Harpers Ferry, purely for defensive reasons.

In addition:

Upon getting the first complaints about supplies not arriving (which McClellan mentioned to him by the 7th, if not earlier) he should have conducted a genuine investigation, such as by telegraphing individual corps commanders as to the scale of their deficiencies.



McClellan


This is a little harder as it involves politics. The supply crisis is almost insurmountable without McClellan leaving the army and putting his case to Lincoln personally (and Lincoln seems not to have noticed the crisis at the time, despite his carriage being right next to a food riot).

The permissions issue is a little easier, but still hard. About the only solution I can come up with is for McClellan to submit a plan with the note that it will be followed unless Halleck specifically rejects it, though this requires McClellan to conclude that Halleck is being duplicitous.

It seems however that McClellan is at all times making efforts to advance the possibility of an offensive movement according to his best judgement on the appropriate offensive movement under the conditions that then obtain. This does not mean he is nagging Halleck to let him move, because there is an ongoing supply crisis (which he IS nagging Halleck about resolving) and the resolution of that crisis is required to make an offensive movement as efficacious as possible.

His problem, or blind spot, is in the politics.



The Emancipation Proclamation

Speaking of politics, it is around this time that the Preliminary Emancipation Proclamation is issued.
These facts at least seem clear:

- The EP was not popular at the time, at least with the population as a whole, and Lincoln himself confessed his disappointment at the public reaction.

- McClellan himself did not approve of the proclamation.

- McClellan made a proclamation to the army to the effect that it was every soldier's duty to obey the acts of the government, that "discussions by officers and soldiers concerning public measures" should be kept to "temperate and respectful expressions of opinion", and that the only legitimate remedy for political error should be the ballot box.


This is often construed as McClellan coming out against the Emancipation Proclamation. It is however instead an expression that, regardless of whether or not he (or anyone else in the army) agreed with it then their role should be to obey the orders of the civilian government.

Effectively McClellan is saying "if you don't like them, vote them out". Given the climate at the time (when many in the North were either in favour of, or worried about, a general becoming a dictator in the Napoleonic vein) and the fact that McClellan was known to be a Democrat (i.e. not Lincoln's political party) and to be adored by his army to a greater extent than they liked Lincoln, the very fact he's saying this is a reaffirmation of the principles of democratic rule. He can't be more in favour of the Emancipation Proclamation without saying he approves (which would be both a political statement and a lie), and remaining silent would allow the political arguments taking place in the army to continue without dampening them down.




Conclusion


In the period from the end of the Maryland Campaign to the opening of the Loudoun Valley campaign about a month later, McClellan wanted to advance into the Shenandoah (where Lee was). Lincoln and Halleck both disapproved of this plan, and Halleck's lack of willingness to either approve it or formally reject it combined with a very real supply crisis to create a situation where McClellan could not unilaterally advance except at great risk to his supply-deficient army.
 

Saphroneth

Major
Joined
Feb 18, 2017
Correction - it seems that Lincoln's idea of the "direct route" to Richmond was explicitly to go via Fredericksburg. This means that bridging the Rappahannock there is a necessity, which just adds many days to the movement - witness the incredible delay at Fredericksburg historically!
 
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