Antietam

[Saphroneth]

I think McClellan declared in one of his reports that he was positioned to go either north, west or south form the position he occupied before being relieved of command by Burnside. According to Mac the direction would have been determined by Lee's actions. Mac already had Pleasanton's cavalry across the Rappahannock and I believe there's a mention of a skirmish around Culpepper Courthouse in which some of Longstreet's forces were repelled. Taking a cue of how proud Mac was of his conduct of the campaign I believe he would have seeked a battle with Lee before Jackson could have joined him as long as it didn't take his army beyond Gordonsville. According to Pendleton's Memoirs Lee was planning to make his stand at Robertson's River, which is about 15 miles SE of Culpepper Courthouse. This would have made a battle possible, if not probable. One thing that has to be taken into consideration is Mac propensity to over estimate the force he's facing - thus causing him to panic - and begin demanding reinforcements before beginning the battle.

As of the time we're talking about, McClellan has hard intel fixing the positions of Jackson's individual divisions. Those divisions are:

DH Hill at Front Royal
AP Hill at Berryville
Jackson's other two divisions at Winchester

What this means is that McClellan knows, beyond a shadow of a doubt, that half of Lee's army is in the Shenandoah.

Now, historically on the 17th at Antietam McClellan committed to very heavy attacks - as of dawn on the 17th he's committed all but two divisions with his army to the attack, and that attack goes in before his reinforcements (three divisions) come in - as the reinforcements come in he commits another division to the attack, that being Richardson which was released when Morell came into view.

Here McClellan knows that half of Lee's army is days away; if he catches Lee and Lee doesn't pull back, McClellan is going to attack. If Lee stands at Robertson's River then he's getting crushed, which is why I think Lee pulls back at least to Gordonsville.

In September?

Yes.

Here's the position map for 30th September:

If McClellan's main body goes for Winchester, and 5th and 6th Corps go for Martinsburg to the north, then there are basically these options.

Option one: Lee holds position with both corps. Both corps get hit at roughly 3:2 odds. (odds ratio approx.)
Option two: Lee pulls back Longstreet to Winchester and holds at Winchester. Lee gets hit at roughly 3:2 odds.
Option three: Lee pulls back Longstret to Winchester and then evacuates further south. No battle.
Option four: Lee piles his whole army north to pounce on 5th and 6th Corps. 5th and 6th Corps get hit at roughly 3:2 odds, but then McClellan's main body can pile into Lee's rear.

 

[Saphroneth]

Two of Burnside's 9th Corps divisions held bridgeheads over the river on the far bank, supporting the cavalry. Lee tasked Stuart and McLaws to drive in the cavalry, and they stopped when they found entrenched infantry south of the river. When Burnside assumed command he withdrew these divisions.

I think Saph has some good maps which he can post.

Yep, well, sort of.


Map as of McClellan's relief:

Maps of the marches of the 6th, 7th, 8th and 9th:

The above map is the map for the 7th; this is the day McClellan was relieved. Some corps stop moving, but McClellan had given march orders and the remaining corps still in motion followed his orders for the 8th and 9th:

The Waterloo bridge is under repair and strengthening, and in addition to that McClellan has a strong cavalry screen out taking the fords of the Hazel (to the south, it's a tributary of the Rappahanock).
In addition to the above, elements of 3rd Corps are arriving at Warrenton Junction. 11th Corps is just off the map above to the east, defending the supply depot on the Manassas Gap railroad.




Also, the map showing where Lee's latest intel as of a day or so after McClellan's relief (in his letter to Jackson) indicated he thought McClellan's infantry was:

Lee has badly misread McClellan's position, and though he's likely to find out pretty soon if McClellan keeps moving it's quite possible he doesn't find out until dangerously late. If Lee's first warning of McClellan's infantry movements is when McClellan's infantry divisions cross the Hazel around Rixeysville and the Rappahanock at Rappahanock station then McClellan's only a day's march from Culpeper.





If anyone's interested, I can give a go at trying to plot out how McClellan's movements could look, in my opinion, based on what Lee's doing.
You'd need to say what you thought Lee's movements would be; I'd follow the rules of
- Corps following the same road do so at a separation of 7 miles
- No more than 10 miles per day of movement per day, corps average
- McClellan starts out trying to englobe Culpeper until Lee abandons it

And would also assume that 6th Corps would head off to Fredericksburg via the Wilderness.

 

[Saphroneth]

What was the mental and physical condition of McClellan's force after the battle ?

1st, 2nd, 9th, 12th Corps - pretty shattered on the 18th, but able to manoeuvre again on the 19th; probably not back to nominal for a while, though (the army didn't sit idle after Antietam, it was drilling more or less constantly to actually do the work of forging it into a cohesive whole - work that got skipped before Antietam owing to the urgency of the campaign).
5th Corps and 6th Corps (counting Couch as part of 6th) were in better shape than the others, and they're the ones which McClellan taps for the independent work in the 19th-22nd period.

 

[GwilymT]

View attachment 371432

Is there a source for this?

 

[Saphroneth]

Is there a source for this?

It looks like it's written by the person themselves, since the misspelling ("Landscapr Turned Red") allows for easy searching.

Honestly I think considering Humphreys fit to fight on the 18th is a bit of a questionable prospect, since they were thrown together on the 12th and departed Washington on the morning of the 14th.
This means that in the course of their marches of the 14th, 15th, 16th and 17th, plus the marching on the 18th which let them reach Antietam, totalled about 65-70 miles (to get to by the Middle Bridge) - which is a hell of an achievement for men where 7 out of the 8 regiments making up the division had been under drill for only about a month. To expect them to come straight off that forced-march and go into battle at anything like the effectiveness of veterans would, I think, be asking too much.

 

[GwilymT]

Yeah, it doesn't seem like even veterans would be worth much after that march let alone green troops.

 

[Saphroneth]

Yeah, it doesn't seem like even veterans would be worth much after that march let alone green troops.

It does actually raise the question of how much Morell's men are worth. They'd done pretty much the same march but having left a couple of days sooner (they caught up with the army late on the 16th I believe, then had a few hours' march to reach the Porter Bridge)... so they had had a bit of rest but - well, probably for the best they were the reserve division. It might be reasonable to consider them as "not available" in the morning's fighting on the 17th.

 

[Saphroneth]

So here's what I think is an interesting question - which is to ask whether there were any flaws in McClellan's operational conception. I've often seen it said that he had a great opportunity as a result of SO 191 but threw it away, but that simply doesn't seem to be the case based on the operational movements.

This is the content of SO 191, which expires on the 12th. (McClellan gets it on the afternoon of the 13th.)

This is the situation McClellan can glean from SO191 (red) and the true positions (orange), plus where McClellan's corps are at the time.


Before continuing, it's worth realizing that if Lee does literally nothing to react to McClellan then almost half of his army is safe. Jackson, Ewell, AP Hill and Walker are south of the Potomac, totalling 16 brigades.
If everything becomes a complete disaster, Longstreet (9 brigades) can retreat over the Potomac at Williamsport before McClellan can possibly reach him.
DH Hill can be hit, but if he wants to then he, too, can fall back - this time to Shepherdstown via Boteler's Ford.
The only part of the Army of Northern Virginia which is truly vulnerable to being trapped is McLaws (which is his division and Anderson's, a total of 10 brigades).


If what Lee wants is to avoid defeat, or minimize the damage to his own army, he can just pull back and effectively abandon McLaws and Anderson (if, that is, Harpers Ferry holds out until relieved). The result of that would be a loss of a quarter of his army, but that's better than losing the whole thing!

McClellan's movements are:

Which is, of course, an attempt to capitalize on the Confederate vulnerability. Lee orders the HF siege abandoned, but Jackson disobeys orders and takes the place the next morning.

This means that after South Mountain the situation is like this:

At this point, if Lee is afraid of destruction, he could simply keep going - retreat over Boteler's Ford - and he's escaped.

The fact that Lee stayed in Maryland until overnight on the 18th indicates to me that he had a reason to do so. He could have wanted to:

- Inflict attrition on McClellan's force, by letting McClellan attack him, and cause more cost to McClellan's army than McClellan inflicted on his (in relative terms).
- Actually defeat McClellan, destroying or severely wounding his army.
- Hold off McClellan's pressure while reuniting his army, and then move north into Pennsylvania.
- Hold off McClellan's pressure until his wagons were over the Potomac.

Without at least one of those reasons, Lee's actions not only make no sense but are actively suicidal. He may not have had a true appreciation of the size of McClellan's force relative to his own (such as not knowing how big his own army was) and thus thought one of those reasons was more plausible than it was in truth, but internally he must have had at least one of those reasons.


With hindsight I think we can say that there was a not insignificant chance that Lee's army could have been destroyed or at least mauled at Antietam. I don't mean that in the sense of "he missed his chance", but in the probabilistic sense - McClellan's actions, Lee's actions and the situation combined to create a battle in which there was some probability (5%, 10%, 20%, 40%?) of Lee's army being destroyed or severely damaged.

This, I think, means that Lee either misjudged that probability (i.e. he thought the probability was, say, 5%, when it was truly, say, 20%) or that he correctly judged the probability but saw it as sufficiently small that it was worth trying for his objective/s.


Could McClellan have acted to further increase that probability, on the operational scale? If the result was that Lee decamped across the Potomac on the night of the 15th or the night of the 16th, is that a better result than historical?

 

[Mango Hill]

You can supply about 20-25 miles away from a rail terminus - if you have the rail line to Harpers Ferry (i.e. over the Monocacy) intact and you have a bridge at Harpers Ferry you can operate about as far as Winchester. The problem is that without the Monocacy bridge repaired and without the HF bridge in place then to get to Winchester you're operating twice as far from a rail terminus as you can supply.

Sorry for not addressing this previously but I must challenge the assertion made above. That 20 - 25 mile limit was made in McClellan's report for his forces at the time. That has to be questioned on the fact that McClellan directed Porter to occupy Shepherdstown on the 21st without knowing what enemy force Porter would face. McClellan cautioned Porter that prior to his advance Pleasanton's cavalry be sent out to scout the area for enemy and to proceed with caution. It just so happens that Shepherdstown is about that distance from HF. As it turned out neither Porter or any other force capable of cutting any major confederate force was not sent out during this allegedly crucial period in September that would have cut off Longstreet at Martinsburg. The only force that received orders in the post Antietam period prior to October - that was larger than a cavalry reconnaissance - was sent at 10:45 PM to Sumner. This order directed Sumner to send out "a brigade of infantry, with a battery of artillery, and sufficient cavalry" towards Leesburg which is SW of HP.

In McClellan's Report beginning on p. 69 it will become quite clear that McClellan had no intention of pursuing his advance towards Winchester any time soon. In fact, he wanted to wait until after the Potomac was unfordable before making a move towards Winchester. He wanted to remain on the defensive, to receive more troops, more supplies, to cut down on stragglers, to build a permanent RR bridge in HF, to train new troops, etc. There's no better evidence of this than McClellan's own Report of the 27th of September. This report prompted Halleck and Lincoln action. Lincoln went to visit McClellan on October 1st for the purpose of getting him to move. Although there's only McClellan's version of that meeting it's clear from Halleck's Report that urging McClellan was at least a part of that meeting.

The purpose of what I've posted is to erase any notion that if not for Halleck holding him back McClellan would have advanced in late September to cut off Longstreet at Martinsburg. McClellan's plan was to secure HF so what happened to Miles did not happen to him and to secure the fords along the Upper Potomac from any flanking movement by Jackson. He didn't think the AOP was in any condition to go on the offensive at the time.

 

[Mango Hill]

Two of Burnside's 9th Corps divisions held bridgeheads over the river on the far bank, supporting the cavalry. Lee tasked Stuart and McLaws to drive in the cavalry, and they stopped when they found entrenched infantry south of the river. When Burnside assumed command he withdrew these divisions.

I think Saph has some good maps which he can post.

Thanks for the info. I recall reading something similar. Yes, Saph is a Wizard of the Maps!

 

[Saphroneth]

Sorry for not addressing this previously but I must challenge the assertion made above. That 20 - 25 mile limit was made in McClellan's report for his forces at the time. That has to be questioned on the fact that McClellan directed Porter to occupy Shepherdstown on the 21st without knowing what enemy force Porter would face. McClellan cautioned Porter that prior to his advance Pleasanton's cavalry be sent out to scout the area for enemy and to proceed with caution. It just so happens that Shepherdstown is about that distance from HF. As it turned out neither Porter or any other force capable of cutting any major confederate force was not sent out during this allegedly crucial period in September that would have cut off Longstreet at Martinsburg. The only force that received orders in the post Antietam period prior to October - that was larger than a cavalry reconnaissance - was sent at 10:45 PM to Sumner. This order directed Sumner to send out "a brigade of infantry, with a battery of artillery, and sufficient cavalry" towards Leesburg which is SW of HP.

Don't forget that there's also Hagerstown, that's also a viable supply node as it's the end of a railway (and was how 5th and 6th Corps supplied themselves during the October lacuna). But I don't see anything contradictory in McClellan aiming to do this:

(the arrows for 5th and 6th Corps may represent threat as much as a real planned movement)
Hagerstown to Martinsburg is about 20 miles when going via Williamsport, and about 25 miles when going via Sharpsburg and Shepherdstown. Harpers Ferry itself to Winchester is about 28-30 miles, but of course a railway runs that way so you can gain a few extra miles that way.

Once the rail line from Frederick Junction to Harpers Ferry is repaired and there's a good bridge at Harpers Ferry, you can advance the way indicated without worry - even if the river rises, your forces striking at Martinsburg have a "way out" because Martinsburg is about 18-20 miles from Harpers Ferry. But before that happens you can supply to Martinsburg and Harpers Ferry (HF is about 20 miles from Frederick Junction) but no further south - not reliably.

I suspect McClellan's plans were in flux somewhat until he decided on the offensive plan towards Winchester, certainly, but I can also see how the Winchester plan was supposed to be supplied. Possibly he was expecting the bridge thing to take only a few days rather than being unresolved about a month later.


As for why McClellan didn't launch it - well, it's those supply concerns.

 

[Mango Hill]

What was the mental and physical condition of McClellan's force after the battle ? Beauregard could have walked into Washington following the humiliation of Union forces at first Manassas /Bull Run .but did anyone esp Davis or his cabinet question why he did not follow McDowell into the Capital ?Then the same with Meade at that other misopportunity battle.The reason why George is so infamous is because he is remember for his campaign against Richmond ,that was a real success.Then what happened with the second chance ?Every general has his one battle be he Alexander,Julius,Lee,or even Grant.But to be successful one does not continue not to learn from defeat.

I think the troops were in better condition than many of the Corp commanders. Burnside was a wreck, although he would dispute that. Sumner, well, he was old and too flustered to have continued in command of anything. Besides that his 2nd Corp had suffered the largest amount of casualties. Hancock would have been counted on to pursue an offensive as well as Franklyn's 6th Corp. There was Porter's 5th Corp, Humphrey's 8 regiments (7 of which were new and inexperienced) could have been used as a reserve if needed. Plus there was Pleasanton's cavalry. Lee was in worse condition and I believe McClellan had enough forces available to bottle up Lee between Antietam Creek and the Potomac if Mac had handled his troops properly.

I disagree that any CSA force could have just "walked into Washington" after the battle. There was a small pursuit of cavalry but it fizzled out and Beauregard's and Johnston's forces were spent.

McClellan's biggest problem was that he was an outspoken antagonist of the administration's policy and thought he should be directing policy. This didn't go well with the Lincoln administration and many of the very influential Radical Republicans that ran the Congressional Committee for the Conduct of the War.

 

[Mango Hill]

Is there a source for this?

Sorry. I copied and pasted from a Note app. Which part in particular do you need a source for?

 

[Saphroneth]

McClellan's biggest problem was that he was an outspoken antagonist of the administration's policy and thought he should be directing policy. This didn't go well with the Lincoln administration and many of the very influential Radical Republicans that ran the Congressional Committee for the Conduct of the War.

Was he?

This is a serious question. Was McClellan actually an outspoken antagonist at this time?

Obviously he probably was later on, Presidential campaign and all, but I don't think it's the case in this period. This is because the Harrisons Landing letter is (1) a private letter, (2) full of suggestions, and (3) McClellan asked Lincoln if he could offer the suggestions before writing it, and subsequently handed it to Lincoln personally.

Lee was in worse condition and I believe McClellan had enough forces available to bottle up Lee between Antietam Creek and the Potomac if Mac had handled his troops properly.

I'm not sure I see the opportunity, I'm afraid. Lee's position is such that he's got Boteler's Ford in his rear; you need to get between Lee and Boteler's Ford to bottle him up in the way you're suggesting, but McClellan simply doesn't have the troops to throw across a cordon while still shielding his northern flank (and, indeed, 9th Corps, which was similarly shattered).


ED: another map!

The positions are a bit approximate, I didn't actually ID all the division locations etc. (the line for Lee's position is actually more like the nightfall 17th positions than the 18th positions) but hopefully this shows how hard it would be to cut Lee off from the Shepherdstown fords.

 

[GwilymT]

Sorry. I copied and pasted from a Note app. Which part in particular do you need a source for?

None, I just didn't know if it was part of a larger work or where you had gotten it. Thanks for clearing it up!

 

[Mango Hill]

I suspect McClellan's plans were in flux somewhat until he decided on the offensive plan towards Winchester, certainly, but I can also see how the Winchester plan was supposed to be supplied. Possibly he was expecting the bridge thing to take only a few days rather than being unresolved about a month later.

Thanks for another great map. Haupt offered to build a temporary RR trestle bridge at HF in late September but Mac nixed it. While not suitable as a permanent structure it could have provided a valuable temporary route of supply.

 

[Saphroneth]

Thanks for another great map. Haupt offered to build a temporary RR trestle bridge at HF in late September but Mac nixed it. While not suitable as a permanent structure it could have provided a valuable temporary route of supply.

I was of the understanding a temporary bridge did get built but then promptly smashed by a freshet, which would presumably make McClellan leery about using it.

More to the point, I was also of the understanding that the rail bridge over the Monocacy hadn't been repaired until October at least - because Lincoln's visit to the army in early October saw him having to switch from a train to a carriage when they reached the Monocacy river. So building a rail bridge at HF would not actually help much, at least by itself.

 

[Mango Hill]

Don't forget that there's also Hagerstown, that's also a viable supply node as it's the end of a railway (and was how 5th and 6th Corps supplied themselves during the October lacuna). But I don't see anything contradictory in McClellan aiming to do this:

Yes, that would get McClellan a battle at Winchester if Lee wants one, and I'm sure he did. Lee even invited a battle at Winchester with the excuse of returning a bunch of wagons and other stuff at Winchester or another place "if you occupy Winchester" (paraphrasing here). This was in early October, I believe the 2nd.

 

[Mango Hill]

Was he?

This is a serious question. Was McClellan actually an outspoken antagonist at this time?

Obviously he probably was later on, Presidential campaign and all, but I don't think it's the case in this period. This is because the Harrisons Landing letter is (1) a private letter, (2) full of suggestions, and (3) McClellan asked Lincoln if he could offer the suggestions before writing it, and subsequently handed it to Lincoln personally.

Well, I might replace outspoken with prominent. His GO 163 was not a ringing endorsement of Lincoln's EP.

I'm not sure I see the opportunity, I'm afraid. Lee's position is such that he's got Boteler's Ford in his rear; you need to get between Lee and Boteler's Ford to bottle him up in the way you're suggesting, but McClellan simply doesn't have the troops to throw across a cordon while still shielding his northern flank (and, indeed, 9th Corps, which was similarly shattered).

What about Pleasanton's cavalry?

 

[Mango Hill]

I was of the understanding a temporary bridge did get built but then promptly smashed by a freshet, which would presumably make McClellan leery about using it.

More to the point, I was also of the understanding that the rail bridge over the Monocacy hadn't been repaired until October at least - because Lincoln's visit to the army in early October saw him having to switch from a train to a carriage when they reached the Monocacy river. So building a rail bridge at HF would not actually help much, at least by itself.

This would require further research on my part. But I have to eat lunch. Of course I don't doubt what you posted but I just have to see it for myself.