Is it fair to say that Fitz John Porter was McClellan's most capable corps commander?

MikeyB

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Sep 13, 2018
Good morning everyone.
After reading some more about the events of 1862, is it fair to say that Fitz John Porter was the most capable corps commander in the East during the McClellan era? Who else would even be an honorable mention? Maybe Hooker? And if so, did Pope and army politics deprive the AoP of a competent commander for the duration of the war?

mike
 
The length of the following periods of twilight at Manassas on 30 August, based on modern definitions, and taking only the morning periods:

Astronomical twilight is 34 minutes long
Nautical twilight is 33 minutes long
Civil twilight is 27 minutes long


Civil twilight is the period when enough natural light remains that artificial light is not needed. Nautical twilight is a period in which it had already been the case for a century that attacks were considered possible, but detailed vision is not possible.

August 30 1862 was five days after the new moon, so lunar illumination would be nonexistent (as the moon would not rise until well into the morning).

I'd guess that it'd be Civil Twilight that the movement would take place, though it could be in Nautical Twilight. So 30-45 minutes of movement by the time Sturgis gets the order; wait long enough that Piatt's men are confirmed turned out and ready to follow the column, and it could reach an hour's delay.

The same concern comes in for Griffin. Morell's order is endorsed with a similar time of reciept.
 
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The order specified daybreak, at sunrise at Richmond was 0532 that day.

This places the twilight periods as:

Sunrise: 0532
Civil twilight: 0505-0532
Nautical twilight: 0432-0505
Astronomical twilight: 0358-0432

As best we can tell, the order reached Porter at 0330, and around 0430 the movement started as best I can tell, i.e. around the beginning of nautical twilight (which is still defined as "daybreak" in the military).
 
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Those times are about right. I used Manassas latitude (which specifies :37 not :32 for sunrise so everything is five minutes off), but didn't give specific times because of the interference of DST (as the modern time at Manassas daybreak August 30 is 0637, owing to DST).


So that makes it:
Porter sends order on to Sturgis between 0330 and 0430
Starts moving around 0430
Morell gets order around 0520
Sturgis gets order 0530

Just waiting for them to confirm reciept would by this theory mean more than an hour's delay in arriving on the field.
 
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So I thought I'd have a look at the places where Porter's command can be questionable. I'll discard the stuff about his letter writing or who he was friends with, and look at the rest.


Porter's first case of an error is during the movement to Yorktown. He and Smith pressure Heintzelman to allow a recce in force for each with their divisions, with Porter's being towards Big Bethel and Smith's being to Ship Point (to attack a battery which did not currently exist). This tipped off the Confederates that large Union forces were on the Peninsula, and Smith, Heintzelman and Porter all come in for blame over it.
This is an error of aggression.

The approach to Yorktown itself sees Porter leading the right flank column, and he doesn't attack "with all his force" as commanded. This decision was sustained by his superiors, and was probably the right call given the actual strength of the defences.

Porter was not at Williamsburg, as he was in the flank force sent up the York.

After his elevation to corps command, Porter's first independent action is Hanover Court House. During this action Porter has most of the Army of the Potomac's cavalry with him, and they're used okay in a battlefield role (taking hundreds of prisoners) but the main flaw Porter has is that when he makes contact with an enemy force he focuses on it as the main enemy force; he exposes his flank to Branch, but that Branch attacked is considered Branch's error in the battle so this might mean the flank security force was proportionate to the needs.
This is fundamentally an error of aggression as well - Porter goes after the first sign of the enemy and focuses in on them. However, he did fulfil his operational objective to clear the road north.
I suspect this is that Porter's new to being an independent commander, as his previous command was all as part of a larger formation.

At Gaines Mill, Porter was originally sufficiently confident that when asked if he needed reinforcements he sent no reply. A reply saying he needed reinforcements could have meant that the Union force held at the end of the day, rather than breaking.

There is no significant error through the rest of the Seven Days to Malvern Hill, though it's noteworthy that he considered advancing after Malvern if certain specifications were met. His performance here is good though.

When the movement back to northern Virginia was conducted, Porter was the first corps out of Harrisons Landing. No complaints about march speed here.

The Northern Virginia campaign we've already discussed, though it's noteworthy that Porter's attack was considered by the targets to be particularly well launched.

During the Maryland Campaign, Porter pursues to Antietam Creek (overtaking the rest of the army with Sykes' division) and handles McClellan's reserves. He's been blamed for encouraging McClellan to be timid, but the conversation usually cited was made up by a journalist.

At Shepherdstown, it's possible Porter could have won the battle, but he was attacked by a force which was on the same scale as his whole corps* and a big part of the problem was that much of his forces were entirely new (the Corn Exchange regiment having never fired their weapons before). You can still argue that it's an error of lack of commitment, though.
* 9 or 10 brigades including AP Hill's division, which means most of the freshest brigades in the Confederate army; Porter has the small mostly-regular division under Sykes, Morell's division (bulked out by new regiments, but fresh) and Humphreys' entirely green division.

Basically, it doesn't look like there's a trend of Porter lacking aggression. On at least two occasions he commits an error of overaggression (Big Bethel and Hanover Court House), possibly three if you include Gaines Mill, and while there are also things which you can consider errors of insufficient aggression that just means they balance out and his aggression looks "normal".
 
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Possible benefits of an attack by Porter on the 29th, and plausibility analysis.

1)
Movement before Longstreet's arrival, as per Pope's original conception, resulting in hitting Jackson in the flank.

Benefit if successful: High. Would force Jackson to retreat towards Sudley Springs.

Risk if attempted under the specified circumstances: Moderate. There is the possibility of Longstreet hitting Porter in the flank in turn (he's got to show up sometime), but otherwise this is a low risk move.

Plausibility: Very low. By the time Porter's forces had arrived at Dawkins' Branch Longstreet was already materially on the field and deploying.


2)
Movement before Longstreet's arrival, resulting in a meeting engagment between Porter and Longstreet or in Porter deploying to prevent Longstreet from reaching the field, meaning that the rest of the battle (with 1st Corps AoV, some of McDowell's divisions and 3rd Corps AoP) can focus on Jackson.

Benefit if successful: Moderate. Porter's forces in a defensive position might be able to hold off Longstreet successfully, depending on assumptions including if he still has Hatch's division. Porter would however be too busy to threaten Jackson's flank.

Risk if attempted under the specificed circumstances: Moderate. Longstreet may be able to overcome Porter in a meeting engagement.

Plausibility: Low. By the time Porter is in position to conduct this movement, Longstreet has arrived in the position; that is, Longstreet has arrived first. He has simply had much less distance to cover.


3)
Attack on Longstreet while Longstreet is still deploying.

Benefit if successful: Moderate to High. If Porter manages to push Longstreet back off the field then he has the ability to wheel against Jackson, though Jackson would surely know he was in danger and have time to pull back.

Risk if attempted under the specified circumstances: Moderate, as above.

Plausibility: Low. Firstly, there is the time issue - the earliest that Porter's corps could possibly leave Manassas Junction (with Hatch's division) is 8:30 if Porter gets moving as soon as he has his order to march to Gainesville (and ignores any objections McDowell raises); Hood's division, leading Longstreet's column, began moving at 6AM. Gainesville is actually closer to Thoroughfare Gap than Manassas Junction, so Longstreet should be expected to begin the deploying "race" first at the critical area.
Secondly there's the numbers problem, with Longstreet disposing of more troops; given Longstreet's numerical advantage then we'd expect him to win a "fair fight" like that.


4)
Attack on Longstreet's corps after Longstreet has arrived, with Hatch, intending to force him off the field.

Benefit if successful: Moderate to High, as above.

Risk if attempted under the specified circumstances: Moderate to High, since if 5th Corps + Hatch is repulsed then it would leave the corps in no fit state for further combat, though it may leave Longstreet in similar problems.

Plausibility: Low. The numerical problems above are retained, though the timing ones are not. A different new one which presents itself however is the Joint Order - once it arrives McDowell will be inclined to take Hatch off in a different direction (as he was historically) and this would make the specified situation unlikely.


5)
Attack on Longstreet's corps after Longstreet has arrived, with Hatch, intending to keep Longstreet in play or prevent him reinforcing Jackson.

Benefit if successful: Moderate, as with (2), it basically keeps Longstreet out of the rest of the fighting.

Risk if attempted under the specified circumstances: Moderate. Simply keeping Longstreet in play permits smaller forces to be committed, which limits the maximum damage that can be suffered; the chance of suffering damage to those forces however may be increased.

Plausibility: Low to moderate. The Joint Order issue remains as specified above.


6)
Attack on Longstreet's corps after Longstreet has arrived, without Hatch, intending to force him off the field.

Benefit if successful: High. In addition to (4), there would be more troops to fight the rest of the battle.

Risk if attempted under the specified circumstances:
Very High. Longstreet would outnumber Porter 5:2 and there is a serious risk of 5th Corps being destroyed.

Plausibility: Very Low, owing to the numerical issue.


7)
Attack on Longstreet's corps after Longstreet has arrived, without Hatch, intending to keep Longstreet in play or prevent him reinforcing Jackson.

Benefit if successful: Moderate, as with (2), it basically keeps Longstreet out of the rest of the fighting.

Risk if attempted under the specified circumstances: High. To keep Longstreet in play would require a significant fraction of Porter's actual corps, and their repulse would largely remove 5th Corps as a unit able to contribute to the battle.

Plausibility: Moderate to High. This is something which Porter has the time, position and proportionate forces to actually do.


8)
Present a flank threat to Longstreet without initially attacking, to either (A) keep Longstreet from moving to support Jackson or (B) if Longstreet does materially commit his forces to an offensive move, profit from the vulnerability thus exposed, or (C) if Longstreet commits part of his forces to an offensive move, keep the forces Longstreet has to retain in Porter's front out of the battle.

Benefit if successful: Moderate in the first case, High in the second. The first one keeps Longstreet out of the rest of the fighting; the second flanks Longstreet. The third could be either Moderate or High depending on how large the covering force is (i.e. if it is large enough that Porter cannot defeat it, Porter has kept it out of the battle; if it is small enough Porter can defeat it, he can then flank Longstreet.)

Risk if attempted under the specified circumstances: Low. Porter can avoid engagement unless there is an opportunity to do damage.

Plausibility: High. This is something which Porter has the time, position and proportionate forces to actually do; it's what he actually did. It also historically gained the benefits of (7) without the risks.




Additional note on proportionate forces: at Cedar Mountain Banks (with ca. 8,000 to 9,000 men by the same scale by which Porter has 9,000 men after Hatch is detached) launches an attack on Jackson in the flank. He is unable to overcome Jackson's ca. 25,000 (by the same scale by which Longstreet has ~24,000 men at Second Bull Run) despite some initial good luck owing to the death of a Confederate general, and is repulsed with heavy casualties.

It is thus not reasonable to me to expect Porter's force to overcome Longstreet frontally, though it may be reasonable to expect Porter to have a good chance if he can hit Longstreet in the flank or rear while Longstreet is also in some way engaged to his front.
 
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So here's a question I've been wondering about.


Let's suppose for a moment that we have a model corps commander - not an ideal one, but a "model" one in the sense of "one we can model". This model corps commander carries out his orders as originally given, and does not make significant errors in following them, but also shows almost no initiative whatsoever - if he has not been explicitly ordered to attack, he will not attack. If he has been explicitly ordered to attack, he will attack even if it is not a good idea.
If he has been ordered to attack under certain conditions, he will follow those conditions.

Now, replace every single one of the corps commanders at Antietam with these model commanders.

What happens?

Do the same at Second Bull Run.

What happens?
 
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So here's a question I've been wondering about.


Let's suppose for a moment that we have a model corps commander - not an ideal one, but a "model" one in the sense of "one we can model". This model corps commander carries out his orders as originally given, and does not make significant errors in following them, but also shows almost no initiative whatsoever - if he has not been explicitly ordered to attack, he will not attack. If he has been explicitly ordered to attack, he will attack even if it is not a good idea.
If he has been ordered to attack under certain conditions, he will follow those conditions.

Now, replace every single one of the corps commanders at Antietam with these model commanders.

What happens?

Do the same at Second Bull Run.

What happens?
VICTORY.
 
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Well, victory happens at Antietam I think, because so much of what went wrong there was corps commanders not following orders (Burnside, Sumner, Hooker etc). At Second Bull Run I think so many of the orders being given were based on an incorrect read of the situation, so it's much harder to tell.
 
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Interesting question. Is there an instance where a corps commander was not a model, in the sense that he did not obey orders when ordered to attack or retreat, which led to victory (or less worse loss) than if the order was obeyed?
 
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Interesting question. Is there an instance where a corps commander was not a model, in the sense that he did not obey orders when ordered to attack or retreat, which led to victory (or less worse loss) than if the order was obeyed?


The tricky thing to clarify here is that I'm not simply referring to someone disobeying orders so much as someone either making a mistake (going in the wrong direction for example) or exercising the normal discretion baked into orders to not follow the original intent.


But the thing you're referring to is basically the merits of initiative. There is certainly a good example of this in the Antietam campaign on the Confederate side, which is that Jackson disobeyed orders when he continued the siege of Harpers Ferry and ultimately forced its surrender - his orders were to basically rush to Sharpsburg.

(There's also an example at Second Bull Run, when McDowell tries blocking Thoroughfare Gap on his own initiative and this delays Longstreet.)

Union corps commanders are often criticized for a lack of initiative, but I'm not so sure that's the problem - I think the problem is that they needed first to actually start following orders properly*, and once that's done then you can talk about instilling initiative...

* within limits; there's not a lot you can do about Pope's orders at 2BR as his model of how the campaign was going was just so flawed.
 
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I also think a basic problem in the Army of the Potomac is there were too many corps commanders which led 2 basic (maybe more) problems. 1) Too many moving parts -- it was unweildy for the army commander and each of them tried some version of "wings" to solve it. 2) It tended to elevate men to corps command that had no business there (thinking of men like Newton and French, but there are certainly other possibly more controversial commanders.

This problem started when Lincoln's special orders created 4 corps and then McClellan crrated 2 provisional corps on the peninsula -- which never went away. Burnside' s, Fremont's, and Banks's independent commands were then added to the mix (9th, 11th, & 12th Corps). The problem was never really solved until Meade convinced the War Department to consolidate the army structure into 3 corps. Burnside's wandering wandering corps joined the Army of the Potomac as an independent command. Also, by this time, the 11th & 12th corps had gone west.

I can think of no other instance in thr war where an army was subdivided into more than 3 or 4 corps.
 
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It's basically two interlocking problems resulting from that March decision about corps, yes. It locked in commanders and they weren't very good ones, because the decisions had to be made before they'd been tested (and then you couldn't get rid of **** ones).



There is at least one case of an army subdivided into more than 3-4 corps, though, Sherman's army outside Atlanta. My count is:


4th Corps
14th Corps
20th Corps
15th Corps
16th Corps
17th Corps
23rd Corps
(plus a cavalry corps)

Sure, these are divided formally into three different armies, but that doesn't alleviate the problem except insofar as you could consider the armies to be basically the wing command level (though they're lopsided if so). But for a lot of the campaign there's the same basic problem that the Army of the Potomac had which is that there's seven distinct corps and they add up to less than 100,000 men, meaning that the corps aren't much bigger than divisions should be.


You could also consider Lee's army outside Richmond to be this from the other direction, which is that several of the "divisions" are actually as big as the Union corps they're facing. The Army of the Valley (Jackson's command) is basically a fairly bulky nine-brigade ~45-regiment corps, but then the rest of the army includes:

DH Hill's division (5 brigades, 23 regiments)
Magruder's Command (6 brigades, 28 regiments)
Longstreet's division (6 brigades, ~25 regiments)
Huger's division (5 brigades, 27 regiments)
AP Hill's division (6 brigades, ~28 regiments)
And the Dept. of NC, which is a rump command with about six regiments.

If these were Union formations they'd be called Jackson's Corps, DH Hill's Corps, Magruder's Corps, Longstreet's Corps, Huger's Corps and AP Hill's Corps. The force is big enough to justify at least four corps though.



There's also an argument to be made that a lot of the corps which are formed (by the Union, but not just by them) during the war don't really fit how corps should work. The ideal for a corps is that it's a self-contained miniature army, which means having multiple subordinate infantry formations with integrated artillery (i.e. divisions) plus at least some cavalry at all times so it can perform scouting duties for itself.
The maximum size is about 30,000, maybe a bit more, while the minimum size is a bit harder to define (as it depends on doctrine). British corps in 1862 were formed of two binary divisions and a cavalry brigade, so it's not very big (about 12,000 men all up) but these corps are definitely fully independent manoeuvre elements in their own right. I can definitely see an argument that if you have a single army of about 30,000 men it might be good to split it in half to provide independent manoeuvre elements, but equally you could just use the divisions in that way.


If I had unlimited latitude to reorg the Union army after Second Bull Run, I think what might work best is to basically take the strongest divisions without regard for corps org, brigade new regiments with old (to bring up the strengths accordingly, but definitely interleave them at the brigade level) and form four corps of about 25,000 men each in three divisions. Attach one cavalry regiment per corps and consolidate all the rest into a cavalry division, with the cavalry division basically being "the cavalry which can act independently"

The point here is that you want to have forces able to be manoeuvred without needing to constantly think about having to support one with another.
 
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  1. Joseph Hooker
    • strong record in Mexico
    • strong record in Civil War at division and corps level
    • record as an organizer/administrator to rival McClellan
    • disliked/not trusted by other commanders
  2. Henry W. Slocum
    • good tough soldier
    • solid battlefield performances 1861-65
    • Gettysburg July 1 command squabble a major negative for me.
    • post-Chickamauga command squabble a major negative for me.
  3. Fitz John Porter
    • good battlefield record 1861-62
    • career truncated by the 2nd Bull Run fiasco
    • booted from Army by court martial; cleared after the war
  4. Edwin V. Sumner
    • maybe promoted too high
    • a dedicated soldier who wanted to fight the enemy.
    • may have saved the AoP at Seven Pines
    • Gets a bit too much of of a bad rap for Antietam
  5. William F. "Baldy" Smith
    • good and bad history from 1862-65
    • squabbled with others too much
    • does not show well as a Corps commander in 1864; maybe combat fatigue or shock from the casualties
  6. James B. Ricketts
    • showed well though-out the war
    • shot 4 times and captured at 1st Bull Run
    • two horses shot out from under him at Antietam; severely injured
    • while recovering, placed on Fitz Porter court-martial; his honest service may have cost him command after.
    • reinstated to command when Grant came East in 1864 commanding a VI Corps division
    • held the left flank at Monocacy
    • disabling chest wound at Cedar Creek, but returned to command his division 2 days before Appomattox
  7. Irwin McDowell
    • I am never sure how to evaluate him
  8. William B. Franklin
    • Grant wanted him to command AoP cavalry; got Sheridan instead
  9. Nathaniel Banks
    1. (generally a bad field commander with 1 positive battle to his credit)
  10. Samuel P. Heintzelman
  11. Erasmus D. Keyes
  12. Joseph K. Mansfield (died too soon to evaluate)
Interesting I wasn't aware that Grant had initially wanted William B. Franklin to command the cavalry before Sheridan came east
 
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I also think a basic problem in the Army of the Potomac is there were too many corps commanders which led 2 basic (maybe more) problems. 1) Too many moving parts -- it was unweildy for the army commander and each of them tried some version of "wings" to solve it. 2) It tended to elevate men to corps command that had no business there (thinking of men like Newton and French, but there are certainly other possibly more controversial commanders.

This problem started when Lincoln's special orders created 4 corps and then McClellan crrated 2 provisional corps on the peninsula -- which never went away. Burnside' s, Fremont's, and Banks's independent commands were then added to the mix (9th, 11th, & 12th Corps). The problem was never really solved until Meade convinced the War Department to consolidate the army structure into 3 corps. Burnside's wandering wandering corps joined the Army of the Potomac as an independent command. Also, by this time, the 11th & 12th corps had gone west.

I can think of no other instance in thr war where an army was subdivided into more than 3 or 4 corps.
And the First and Third Corps had been decimated badly at Gettysburg so a few of the divisions from those corps were transferred to II and V Corps prior to the Overland Campaign. There was Wadsworth's division that had the Iron brigade in the 5th Corps in 1864 and David B. Birney's division from the 3rd Corps was transferred to Hancock's command. Although Francis C. Barlow had commanded a brigade in the XI Corps under Howard at Gettysburg, he did not go west to with the rest of the corps to relieve Chattanooga because he was commanding a division under Hancock just before the Army of the Potomac marched off into the Wilderness. And the 9th Corps, Burnside's old command was outside of the army's command structure in 1864 directly reporting to Grant, not the way the II, V, and the VI corps reported to Meade then to Grant but by the siege of Petersburg the 9th Corps had to report directly to Meade
 
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It's basically two interlocking problems resulting from that March decision about corps, yes. It locked in commanders and they weren't very good ones, because the decisions had to be made before they'd been tested (and then you couldn't get rid of **** ones).



There is at least one case of an army subdivided into more than 3-4 corps, though, Sherman's army outside Atlanta. My count is:


4th Corps
14th Corps
20th Corps
15th Corps
16th Corps
17th Corps
23rd Corps
(plus a cavalry corps)

Sure, these are divided formally into three different armies, but that doesn't alleviate the problem except insofar as you could consider the armies to be basically the wing command level (though they're lopsided if so). But for a lot of the campaign there's the same basic problem that the Army of the Potomac had which is that there's seven distinct corps and they add up to less than 100,000 men, meaning that the corps aren't much bigger than divisions should be.


You could also consider Lee's army outside Richmond to be this from the other direction, which is that several of the "divisions" are actually as big as the Union corps they're facing. The Army of the Valley (Jackson's command) is basically a fairly bulky nine-brigade ~45-regiment corps, but then the rest of the army includes:

DH Hill's division (5 brigades, 23 regiments)
Magruder's Command (6 brigades, 28 regiments)
Longstreet's division (6 brigades, ~25 regiments)
Huger's division (5 brigades, 27 regiments)
AP Hill's division (6 brigades, ~28 regiments)
And the Dept. of NC, which is a rump command with about six regiments.

If these were Union formations they'd be called Jackson's Corps, DH Hill's Corps, Magruder's Corps, Longstreet's Corps, Huger's Corps and AP Hill's Corps. The force is big enough to justify at least four corps though.



There's also an argument to be made that a lot of the corps which are formed (by the Union, but not just by them) during the war don't really fit how corps should work. The ideal for a corps is that it's a self-contained miniature army, which means having multiple subordinate infantry formations with integrated artillery (i.e. divisions) plus at least some cavalry at all times so it can perform scouting duties for itself.
The maximum size is about 30,000, maybe a bit more, while the minimum size is a bit harder to define (as it depends on doctrine). British corps in 1862 were formed of two binary divisions and a cavalry brigade, so it's not very big (about 12,000 men all up) but these corps are definitely fully independent manoeuvre elements in their own right. I can definitely see an argument that if you have a single army of about 30,000 men it might be good to split it in half to provide independent manoeuvre elements, but equally you could just use the divisions in that way.


If I had unlimited latitude to reorg the Union army after Second Bull Run, I think what might work best is to basically take the strongest divisions without regard for corps org, brigade new regiments with old (to bring up the strengths accordingly, but definitely interleave them at the brigade level) and form four corps of about 25,000 men each in three divisions. Attach one cavalry regiment per corps and consolidate all the rest into a cavalry division, with the cavalry division basically being "the cavalry which can act independently"

The point here is that you want to have forces able to be manoeuvred without needing to constantly think about having to support one with another.
Yes Sherman's army occurred to me, but ultimately I think the organizational command structure into three separate armies/commands makes the case somewhat different.

Grant eventually had a similar structure in Virginia with the Army of the Potomac and the Army of theJames.
 
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It was the summer of 1862 between the Battle of the Seven Days and Second Bull Run, Philip Kearny devised the first unit insignia patches used in the army. He issued an order that his officers should wear a patch of red cloth on the front of their caps to identify themselves as members of his unit. Daniel Butterfield who was army's chief of staff under Hooker and Meade was credited with taking Kearny's idea and standardizing it for all the corps in the Army of the Potomac, designing most of the corps badges. After Kearny was killed at Chantilly after the battle of Second Bull Run, there were rumors in Washington that Lincoln was contemplating replacing McClellan with Kearny in command of the Army of the Potomac if he had survived since Kearny had gone to the aid of John Pope's Army of Virginia at Bull Run
 
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It's basically two interlocking problems resulting from that March decision about corps, yes. It locked in commanders and they weren't very good ones, because the decisions had to be made before they'd been tested (and then you couldn't get rid of **** ones).



There is at least one case of an army subdivided into more than 3-4 corps, though, Sherman's army outside Atlanta. My count is:


4th Corps
14th Corps
20th Corps
15th Corps
16th Corps
17th Corps
23rd Corps
(plus a cavalry corps)

Sure, these are divided formally into three different armies, but that doesn't alleviate the problem except insofar as you could consider the armies to be basically the wing command level (though they're lopsided if so). But for a lot of the campaign there's the same basic problem that the Army of the Potomac had which is that there's seven distinct corps and they add up to less than 100,000 men, meaning that the corps aren't much bigger than divisions should be.


You could also consider Lee's army outside Richmond to be this from the other direction, which is that several of the "divisions" are actually as big as the Union corps they're facing. The Army of the Valley (Jackson's command) is basically a fairly bulky nine-brigade ~45-regiment corps, but then the rest of the army includes:

DH Hill's division (5 brigades, 23 regiments)
Magruder's Command (6 brigades, 28 regiments)
Longstreet's division (6 brigades, ~25 regiments)
Huger's division (5 brigades, 27 regiments)
AP Hill's division (6 brigades, ~28 regiments)
And the Dept. of NC, which is a rump command with about six regiments.

If these were Union formations they'd be called Jackson's Corps, DH Hill's Corps, Magruder's Corps, Longstreet's Corps, Huger's Corps and AP Hill's Corps. The force is big enough to justify at least four corps though.



There's also an argument to be made that a lot of the corps which are formed (by the Union, but not just by them) during the war don't really fit how corps should work. The ideal for a corps is that it's a self-contained miniature army, which means having multiple subordinate infantry formations with integrated artillery (i.e. divisions) plus at least some cavalry at all times so it can perform scouting duties for itself.
The maximum size is about 30,000, maybe a bit more, while the minimum size is a bit harder to define (as it depends on doctrine). British corps in 1862 were formed of two binary divisions and a cavalry brigade, so it's not very big (about 12,000 men all up) but these corps are definitely fully independent manoeuvre elements in their own right. I can definitely see an argument that if you have a single army of about 30,000 men it might be good to split it in half to provide independent manoeuvre elements, but equally you could just use the divisions in that way.


If I had unlimited latitude to reorg the Union army after Second Bull Run, I think what might work best is to basically take the strongest divisions without regard for corps org, brigade new regiments with old (to bring up the strengths accordingly, but definitely interleave them at the brigade level) and form four corps of about 25,000 men each in three divisions. Attach one cavalry regiment per corps and consolidate all the rest into a cavalry division, with the cavalry division basically being "the cavalry which can act independently"

The point here is that you want to have forces able to be manoeuvred without needing to constantly think about having to support one with another.
The corps system I think may have been modeled on Napoleon's La Grande Armee that was organized into six corps in 1804
 
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Well, yes, obviously this is the basis, but there was a reason behind it. A corps is meant to be the largest self-contained force that can fit down a single road in a day.
In it's original conception, it was a self-contained army with it's own artillery, cavalry, engineers etc.

The ACW Corps is a shadow of the European Corps.
 
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In it's original conception, it was a self-contained army with it's own artillery, cavalry, engineers etc.

The ACW Corps is a shadow of the European Corps.
The closest you get is probably McClellan's original (March 1862) corps, as those each consisted of three divisions with integrated artillery and at least some cavalry. No engineers though.

The Grand Divisions might also briefly approach it.
 
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