"Size of corps per side." Topic

Okay I think I have this right but need someone to confirm it to me if you know. Now I know that troop strength of corps varied depending on casualties, location, etc, etc.
This being said I am thinking that in ideal conditions a Union Corps was around 15,000 and a Confederate Corps was more like 25,000. This sound about right?

I think I know what you mean, but did the CSA actually use corps? My impression is that the divisions were more important to the CSA, and that they tended to be grouped together in a manner that changed so often it might be called ad hoc. Of course, I could be completely off base on this.

Okay let me start over, I have found several sources and they vary. I know that the southern corps usually had one or even two more divisions making them sometimes twice the size of northern corps. The numbers I am seeing vary from 15,000-30,000 standard for the north and from 20,000-40,000 for the south ideally. I am trying to figure out a happy and realistic middle ground.
@mwindsorfw yes, the CSA had mainly 3 "official" corps, all part of the army of Virginia. I am assuming that they had other corps for the west but they where not as well known and may not have even had official numbers because of divisions being moved in and out more then in the east.

The Confederates most certainly used Corps – as noted most famously in the Army of Northern Virginia where they were very, very effective

I agree with your estimates – Confederate corps were larger but Union corps were much more numerous

From June 1862 thru May 1863, Lee had two corps.

Longstreet's had five divisions and Jackson's four.

Anvil and hammer as it were.

You are not going to get anything more than a range, and out of that range you can pick whatever number makes you happy. A Union corps can have a varying number of divisions, a varying number of brigades per a division, and a varying number of regiments per brigade.

I think your numbers are a little high. At Gettysburg Union corps ranged from 9,200 to 13,600, while the Rebel corps went from 20,700 to 22,100. Out west at Chickamauga the Yankees ranged from 5,816 to 16,919, while the Rebs went from 7,716 to 12,544.

The Corps of both armies tended to fluctuate over the war in numbers. There is no real way of putting numbers to them unless you can accurately get the 'average' throughout the war and THAT would be a large task. At certain times the numbers could be very large or very small.

For the AotP the corps sizes ranged from 35,000 plus to as little as 8,000. For the AoNV the numbers are similar depending upon when in the war. Mid-war AoNV the army had two corps and then switched to 3 corps. So easily they would be larger at 2 corps, more like 40,000 to down to 10,000 or much less near the end of the war.

A division in each side operated in the same way but in the AoNV Lee allowed a little more independence to the division commanders, operating under parameters. Under Jackson of course he didn't allow very much of this, he was more strict and secretive with his subordinates. In 1862 when Ewell was a division commander under Jackson he was often annoyed. Jackson would issues specific orders such as, 'Go you point A and await further orders' and not inform Ewell why. In the AotP usually there was less leeway for division commanders uniformly.

Are you really looking for an overall average or a specific period with a particular army?

The Western Corps were more regularly changed due to the shifting command structure. In Virginia there are three main eras of corps organization:

1) The Peninsula campaign 1862, where command groupings shift but eventually (during the Seven Days) end up evolving to a point where Longstreet and Jackson command the two largest groupings.

2) The smaller divisional groupings are mostly merged into Longstreet and Jackson's commands, creating the First and Second Corps which fought in the Northern Virginia Campaign, the Maryland Campaign, the Fredericksburg Campaign, and the Chancellorsville Campaign. The First Corps tended to consist of 4-5 divisions during this period (at Sharpsburg, D.R. Jones', R.H. Anderson's, McLaws', and the small divisions of Hood and Walker), and the Second Corps tended to consist of 4 divisions (at Sharpsburg, Jackson's Old, Ewell's Old, D.H. Hill's, A.P. Hill's). Jackson is mortally wounded at Chancellorsville (spring 1863).

3) Due to that, the Army of Northern Virginia is reorganized into 3 corps under Longstreet, Ewell, and A.P. Hill. Divisions and brigades are moved from both existing Corps to create the new Third Corps (chiefly R.H. Anderson and A.P. Hill's). Each Corps consists of 3 divisions This remains the primary organization throughout the rest of the war; the First and Third Corps remain under Longstreet and Hill throughout (Hill is killed retreating from Petersburg at the end of the war), the Second has three primary commanders.

Now, there is a little more complexity in the AoNV in 1864-5; the two strong garrison divisions of Hoke and Bushrod Johnson form the Fourth Corps under R.H. Anderson in the defence of Petersburg, whilst the small division of Breckinridge chiefly fights alongside Second Corps in the spring and summer campaigns, and travels with Second Corps to the Valley in summer 1864. In that campaign, Second Corps and Breckinridge's division, plus two cavalry divisions, form the Army of the Valley; the four infantry divisions are split down into two "corps", which are, however, fairly small, and do not survive the recall of the Second Corps to Petersburg. There was also an organization formed from Department of Richmond troops under Ewell called only "Ewell's Corps", which during the retreat from Appomattox had other troops attached to it operationally, but this was a short-lived and insignificant organization.

By the end of the war, prior to the Appommattox campaign, the three main Corps of the Army of Northern Virginia would have fielded about 15-16k (the Fourth Corps, though with fewer divisions, would have had about 14k prior to Hoke returning to North Carolina). This is much reduced from the campaigns of 1863 and 1864 where they would have had more like 22-24k each.

I won't go into such dull detail about the Union Corps, but initially in the East they would have been smaller individually than the Confederate Corps; at Gettysburg the I Corps had 7 brigades, the II Corps 10 brigades, the III Corps 6 brigades, the V Corps 8 brigades, the VI Corps 9 brigades, the XI Corps 6 brigades, and the XII Corps 6 brigades. The Confederate Corps had 11, 13, and 13 respectively. However, in 1863-4 Grant reorganized the Army of the Potomac, with the I and III Corps being merged into the V and II Corps respectively. By the end of the war they would have fielded 18-20k, making them numerically larger than the Confederate Corps facing them.

Thank you guys so much for the input. Some of this I have researched, some I have not. The comments support my original thoughts that since I want an average I can use for the whole war I will have to settle on a "happy medium" in the middle.

And then there is the war in the West. Much different. For instance: The Army of Tennessee (Bragg) at Chickamauga had 5 corps: Polk, D. H. Hill, Buckner, Walker, and Hood; each composed of 2 divisions. But there was a great deal of difference in the sizes of the divisions. Also 2 cavalry corps: Wheeler and Forrest, of two divisions each.

At the same battle, the Army of the Cumberland (Rosecrans) consisted of 4 corps: 14th (Thomas) of 4 divisions; 20th (McCook) 3 divisions; 21st (Crittenden) 3 divisions; and Reserve (Granger), consisting mostly of rear-area garrisons, but with 3 brigades on hand for the battle. Also a Cavalry Corps of 2 divisions, but 1 brigade (Minty) operated independently; and 1 brigade of 14th Corps (Wilder) was mounted infantry, also operating independently.

(No real corps in the Far West/Trans-Mississippi.)

Much of this depends on when and where in the War. In early 1864 for example the number of Corps in the Army of the Potomac was reduced when the First and Third Corps were eliminated and their units folded into other Corps. The Eleventh and Twelfth Corps were also sent to the West after Gettysburg, they would eventually be rolled together into a single Corps. There are no hard and fast rules that apply for the whole war.

What jowady said. For instance, at one point, Grant's entire Army of the Tennessee was a single corps, the 13th, and Rosecrans' entire Army of the Tennessee was the 14th (although it was unofficially divided into 3 "wings"). On the other hand, the 4th Corps continued to exist, in name, on the Peninsula for months after 1 of its 2 divisions had gone with the Army of the Potomac and been merged into the 6th Corps.

A note : the reorganization of the Army of the Potomac was done by Meade before Grant came east.

I think the question is sort of like asking the size of the typical American family: 4.5. Now, while that's the average, you NEVER see a family that size.

So close to Washington, the Eastern Theatre saw the most political 'interference' by the Union Government. With all the requests for command from constituents and Washington's mistrust of West Point graduates after half defected to the South, there was a need for lots of regiments and brigades…hence the large number of both in the AoP. In the end, the Union created 1/3 more regiments compared to the South [from the same number of troops].

The West enjoyed some distance from Washington and Richmond, so there wasn't as much influence in how armies were organized, so both sides had similar sized corps, divisions and brigades.

In the Federal Army, at least early period, corps commands were signed into being by the President. This had the side-effect that an army commander could not fire a corps commander.

Hence in 1864 Burnside still bore his order assigning him as commander of 9th Corps signed by Lincoln and Grant could not fire him even though he wanted too.

Also allow me to state that before the October '62 reorganisation Lee's army had 3 corps, under GW Smith, Longstreet and Jackson. For Maryland GW Smith was too ill to take to the field, and so the senior division commander, DH Hill, took it to the Potomac river with its three divisions (DH Hill, Walker and McLaws).

The three corps organisation was that preferred by Lee. When Davis asked Lee to nominate his Corps Commanders as the grade of Lt Gen was approved he named Longstreet, Jackson and AP Hill. Davis's reply is lost, but it can be surmised that Davis told Lee to obey seniority, and DH Hill was senior to AP Hill. Lee then adopted the two corp structure. Lee was already reorganising into three corps for his three favoured commanders before Jackson bought it, and had Jackson not been shot the ANV would have gone into Pennsylvania with an indentical organisation save Jackson vice Ewell (and probably Ewell vice Early in division command).

Grant fired McClernand as commander of the 13th Corps during the siege of Vicksburg, and named Ord to take his place, subject to approval of the President. (He was armed with a message from Stanton to Charles Dana saying that Grant had full authority to fire anybody who impeded his operations. McClernand eventually got command of the 13th Corps back, but only after it had been transferred to the Dept. of the Gulf.)

During the Peninsula campaign, McClellan formed two provisional, or unofficial, corps, the 5th and 6th, in order to get some corps commanders that he liked (Porter and Franklin).

It wasn't Burnside that Grant couldn't fire, it was Butler, as commander of the Army of the James (Dept. of Virginia and North Carolina).

Once again all very good info, thanks again. I hope some of you have enjoyed the topic as much as I have:) My game has been in play test for a year now and has the mechanics running I am now just down to "fine tuning it" and double checking the smaller details that don't change the whole game, like this one. Thanks again. "Surviving the Elephant" is coming along very well:)