The Organisation and Strength of the Cavalry at Antietam

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The Organisation and Strength of the Cavalry at Antietam

Introduction

The organisation of the cavalry during the Maryland campaign is apparently not supposed to be a mystery. The organisation is given thus in the OR:

Cavalry%2B26%2BSept.png


The information here ultimately comes from Pleasonton's Report dated 19th September, but not completed and submitted until the 26th September. Definitive, right?

However, at closer inspection problems with this chart arise, some of which are below.

What is Definitely Wrong with the Orbat?

1st Brigade


Just prior to Antietam the 1st and 6th Cavalry were definitely serving with Franklin's wing. The 1st Cavalry accompanied the 6th Corps to Antietam on the 17th (Freiheit, 454 fn), but the 6th US Cavalry remained on the Maryland Heights and didn't come to Antietam until the 20th.(ref) On the morning of the 18th McClellan issued an order placing the 1st and 6th US Cavalry, plus attached section of horse artillery, under Pleasonton.(ref)

Charles Whiting was a Captain on the 17th September, and was in command of the 5th US Cavalry, not a brigade. On the 19th September turned command of the 5th Cavalry over to Capt JE Harrison, and assumed command of this "regular brigade".

On the 24th, news arrived that Whiting had been promoted to Major of the 2nd US Cavalry (ref), whereupon he assumed command of the detachment of the 2nd US Cavalry with the Army of the Potomac. Whether this "regular brigade" was handed over to Capt. Wm. P. Sanders of the 6th US Cavalry (the next in seniority) or it was dissolved from then is unknown. Sanders was at Antietam as an AdC to Franklin, but his regiment was not, arriving on the 21st from the Maryland Heights.

There is essentially no evidence that a "regular brigade" existed on the 17th September or before. Before the campaign the regular regiment were not grouped together, and after the campaign they were not grouped together. It appears that for a few days after Antietam Pleasanton organised a grouping of all the regulars available, but this was transient.


2nd Brigade

The permanent 2nd Brigade was Pleasanton's Brigade. The 8th Illinois and 8th Pennsylvania were part of Pleasanton's Brigade at Harrison's Landing and moved to Washington together, both landing at Alexandria on the 2nd September. The other regiment of the brigade at Harrison's was the 6th US, which certainly is detached during the campaign, rejoining the brigade on the 21st.


The 3rd Indiana was found on duty where the 8th Illinois was assigned to, and essentially joined the 8th Illinois in a small ad hoc brigade. Pleasanton's report calls this pair of regiments "Farnsworth's Brigade".

The 1st Massachusetts Cavalry came up from Port Royal, SC (or rather 4 sqns of it did) and landed the same day as the 8th Illinois and 8th Pennsylvania. Their history records that they were attached to Farnsworth's Brigade on the 12th at Frederick, making a three regiment brigade.

However, the 8th Pennsylvania Cavalry were not present at Antietam. Their regimental history records that they went with McReynolds to Gettysburg and didn't rejoin the main army until the 18th. They were thus not part of Farnsworth's Brigade on the 17th.

3rd Brigade

The 4th Pennsylvania Cavalry was one of the regiments of Averell's Brigade. The status of the 6th Pennsylvania was apparently still an independent regiment, which it reverted to post-Antietam and was still such at Fredericksburg.

It is possible this temporary brigade could have been created, but Rush, not Childs, would have been the senior colonel. Thus it seems that this pairing was likely a temporary expedient.

This brigade, such as it was, ceased to exist on the 19th when the 6th Pa was assigned independently. (ref)

4th Brigade

This temporary brigade, in its OR form of McReynold's 1st New York Cavalry and the 12th Pennsylvania Cavalry, wasn't formed until the 25th September. Prior the 13th the 1st NY and 8th Pa were acting together as a temporary brigade, and on that date 2 Bns of the 12th Pennsylvania were added.

On the 12th it was correctly reported that Fitz Lee's Brigade was heading to Gettysburg. On 13th September, the 1st NY Cavalry, with the 8th Pennsylvania, "12th Pennsylvania" and a section of the horse artillery, were sent from Frederick in pursuit. Having failed to overhaul Fitz Lee, they arrived at Boonsboro on the evening of the 17th. Thus they weren't at the battle.

The 12th Pennsylvania arrived at the army on the 11th. On the 13th, at least a battalion of the regiment were assigned to Sumner's wing, and apparently remained such during the battle.(ref) The balance of the regiment went with McReynolds on the 13th (ref). The question of command of the detachments is interesting. Both colonels and the senior major were absent, and only the second major (James A. Congdon) and junior major (William Bell) were with the regiment. Veterans recalled that William Bell commanded the detachment at Antietam (ref). Hence Congdon must have been with the main body, as you'd expect.

Hence on the 17th this temporary brigade existed in a different form to the OR.

5th Brigade

This temporary brigade existed on the 21st September, as recorded in the history of the 3rd Pennsylvania, and an order on the 20th from McClellan sent "Davis" to sweep the area in front of Meade.

The 3rd Pennsylvania had arrived at Alexandria on the 8th September, and had joined the army. It was a regiment of Averell's First Brigade (in fact Averell's own regiment).

The 8th NY Cavalry were one of the regiments that escaped Harper's Ferry. They arrived at Greencastle, PA around noon on the 15th. The next day (16th) they rode to Williamsport and were posted to Jones' Crossroads by McClellan's order. On the 17th they rode down to the Antietam battlefield, 4 miles near due south, and found themselves in the rear of the 1st Corps. Hooker being down, they reported to Doubleday as senior commander. (ref)(ref)(ref)(ref).

Thus this brigade can't have existed on the morning of the 17th. One regiment was with Hooker, and the other was en route. It is quite probable that the 8th NY fell in with the 3rd Pa and formed the brigade late on the 17th or a day or so afterwards. This arrangement ceased to exist on the morning of the 23rd when the 8th NY rode to Hagerstown by the 3rd Pa remained near Sharpsburg.

So, What was the Organisation?

Pleasanton's report of the 26th September is clearly wrong in places, and likely represents the temporary organisation of the division on that date in the absence of the other brigadier and the incapacity of the division commander (Buford).

In Averell's absence, McReynolds was the senior colonel and would have become acting brigadier. However, he was sent with half his brigade on a recce to Gettysburg. This would leave Childs in command of the remaining two regiments: the 5th US and the 4th Pennsylvania.

Pleasanton's own brigade had three regiments under Farnsworth. However, Farnsworth was junior to Williams of the 1st Massachusetts.

The 6th Pennsylvania were still independent, yet it's clear they formed a temporary brigade with the rump of Averell's Brigade on the 17th. Thus the organisation of the six regiments under Pleasanton's own command would be:

  • Averell's Brigade, under Col. Childs (then Rush, vice Childs KIA)
    • 5th United States (Capt. Whiting)
    • 4th Pennsylvania (Lt Col Kerr, vice Col Childs, brigadier)
    • 6th Pennsylvania (9 coys) (Col Rush, then Lt Col Smith vice Rush, to brigadier)
  • Pleasanton's Own Brigade, under Col. Farnsworth
    • 8th Illinois (Maj Medill, vice Col Farnsworth, brigadier)
    • 3rd Indiana (Maj Chapman)
    • 1st Massachusetts (Col Williams)
  • Horse Artilley
    • Battery A, 2nd US Artillery (Capt Tidball, 6 Ordnance Rifles)
    • Battery B&L, 2nd US Artillery (Capt Robinson, 4 Ordnance Rifles)
    • Battery M(-), 2nd US Artillery (Lt Hains, 4 Ordnance Rifles)
    • Battery C&G(-), 3rd US Artillery (Capt Gibson, 4 Ordnance Rifles, section with 6th US Cavalry by elimination)
There were four other regiments on the field which weren't escorts/provosts, but did not fight under Pleasanton on the 17th. In all four cases the regiment was attached to a corps. The 3rd Pennsylvania was the only full regiment on the field not under Pleasanton. They were detached from Averell's brigade and were attached to the 1st Corps to screened the 1st Corps as they crossed the Antietam on the 16th. They fired the first (non-artillery) shots of the battle.

The other three regiments were parts of regiments. A battalion of the 12th Pennsylvania Cavalry joined the 2nd Corps at Frederick, and went off on a recce on the 16th. They were deployed as the prisoner-of-war cage during the battle.

A battalion of the 1st US Cavalry was with Franklin, and was the vanguard of his corps. Finally the 1st and 2nd battalions of the 6th NY Cavalry were with 9th Corps and formed the cavalry pushed out on the left wing (like the 3rd Pa formed the right wing flank guard). Sources are mixed on whether 6 or 8 coys were present.
  • 3rd Pennsylvania Cavalry (1st Corps)
  • (3rd?) Battalion, 12th Pennsylvania Cavalry (2nd Corps)
  • Battalion, 1st US Cavalry (Coys, B, C, H & I, attached to 6th Corps)
  • 1st and 2nd Battalions, 6th New York Cavalry (8? coys) (attached to 9th Corps)
There of course were various small detachments serving as escorts etc. At army headquarters were 3 companies; a squadron of the 4th US Cavalry who were McClellan's escort and the Oneida Coy who were a specialised orderly unit. A battalion of the 2nd US Cavalry, with the McClellan Dragoons attached were with the army provost.

Each corps had roughly a squadron attached. The Kanawha division had brought along their own brigade cavalry.
  • 4th US (2 coys, A&E) and Oneida Coy (Army HQ Escort)
  • 2nd US (4 coys, E, F, H & K) with the McClellan Dragoons (2 coys) attached (Army Provost)
  • 2nd NY Cavalry (4 coys, A, B, I & K) (1st Corps)
  • 6th NY Cavalry (2 coys, D&K) (2nd Corps)
  • 1st Maine Cavalry (2 coys, H&M) (5th Corps)
  • 6th Pennsylvania Cavalry (3 coys, B, G & I) (6th Corps)
  • 1st Maine Cavalry (3 coys A, G & I) (9th Corps, G was assigned to protect trains and not on the field, ref)
  • 3rd Ohio Independent Coy (1 coy) (9th Corps)
  • 1st Virginia Cavalry (2 coys, or possibly only one), and Chicago Dragoons (1 coy) (Kanawha Division)
  • Coy L, 1st Michigan Cavalry (12th Corps)
McReynolds' force had been detached with:
  • 1st New York Cavalry (Maj AW Adams, vice Col McReynolds, acting brigadier)
  • 8th Pennsylvania Cavalry (Lt Col AE Griffiths)
  • 2 battalions, 12th Pennsylvania Cavalry (Maj JA Congdon)
  • Chapin's section, Bty M, 2nd US Artillery
There are two more regiments of McClellan's army. The first is the 6th US Cavalry. This was part of the cavalry force with Franklin's wing (with 1st US Cavalry and 3 coys of the 6th Pa Cav). They occupied the Maryland Heights until relieved, and returned to the main army on the 20th (ref).

"About half" the Maine Cavalry along with the HQ were detached at Frederick to protect the depot. It is commonly given as 6 coys, but I am missing a coy in the count and don't know where it is.
  • 6th US Cavalry- Maryland Heights (with a section of horse arty)
  • 1st Maine (6? coys) - Frederick

Voss' Brigade and 15th Pennsylvania Cavalry

Voss' brigade (Cole's Potomac Home Brigade Battalion, det. 1st Maryland, 8th NY, 12th Illinois and 7th RI Sqn) escaped Harper's Ferry and captured Longstreet's Ordnance train at Williamsport. They then headed north to Greencastle, PA arriving on the 15th and sending to McClellan for orders. Col Davis and his 8th NY Cavalry didn't wait and rode to find McClellan on the morning of the 16th and arrived off the right flank sometime in the late morning or early afternoon.

The detachment of the 15th Pennsylvania are listed in the OR, but were at Greencastle, PA with the 1st PHB Cavalry, 7th RI Squadron and a detachment of regular cavalry. In obedience to McClellan's orders, they left Greencastle on the 19th September for Jones' Crossroads, and thus missed the battle.


The Question of Command

McClellan's choice to command the cavalry were starkly limited. It had been exposed that BG Stoneman had a serious medical problem (impacted piles) that kept him from performing the duties of a cavalry leader. Ergo, on 10th September he was reassigned and took command of the infantry division vacated by Kearny. McClellan had three cavalry generals available to him, and needed leaders for two divisions of cavalry; the one which was to accompany him into the field, and the one left screening Washington. He selected Buford and Bayard respectively for these two posts.

However, Buford was still recuperating from his wound received under Pope.The description of the wound suggests strongly that Buford had a broken kneecap. Thus he doesn't appear to have a particularly active role in the battle. During Antietam Buford move forward with Hooker, and exercise command over the cavalry on the Federal right.

As the only other cavalry general with the army, Pleasanton took command of the Cavalry Division almost by default. It would be a month before the returns indicated Buford had taken active command of the whole cavalry division, coinciding with a jump in reported strength for the cavalry, probably as the whole force is now reported.

Strength of the Cavalry

There is very little about the strength of the cavalry known. The OR reports 4,543 PFD in the Cavalry Division on 20th September. It is not clear exactly what organisations this includes. It is clear that it does not include the main body of the 1st Maine Cavalry as they appear under the Frederick entry. Bayard's Brigade at Washington is 1,700 PFD (2,725 grand aggregate) on the same date with the grand aggregate decreasing by 1,532 since 10th September. The troops listed at Williamsport are Kenly's Maryland Infantry who arrived there the night of the 19th.

The major question is whether the Harper's Ferry escapees are included. It is likely that McReynolds' expedition is included.

The last returns for the Cavalry Division in the OR are 10th August and showed 5,176 offrs and men PFD in 9 regiments (excluding the horse artillery). All nine were still part of the division come the end of September, but apparently not mid September; Pleasanton's casualty report for the division sums as follows:

Maryland%2BCav%2BCasualties.png



Missing from this list is the 1st US Cavalry, the regiments attached to Corps (including 3rd Pennsylvania Cavalry) and the Harper's Ferry escapees. McClellan reduced the 20th September return by 231 when describing available cavalry, which would fit the detachment of the 1st US Cavalry. Of the regiments listed, the 8th Pennsylvania was with McReynolds and was only attached to the 2nd Brigade after Antietam. McReynolds was on detached service at Williamsport when this report was made out with the two regiments indicated, and hence never turned in a report.

Thus starting from 5,820 servicable horses and 5,176 PFD in August and taking the men pro-rata, removing the 1st and 6th US, the 3rd and 8th Pa and 1st NY would be 3,070 horses or ca. 2,700 men PFD. Additionally 25% of the 6th Pa are away (ca. 140 men). In round figures 2,300 cavalry PFD remain. To this to add the two regiments that joined the cavalry. The 1st Massachusetts (2 bns) was, according to their history, "nearly 700 strong" or say 600 PFD. The 3rd Indiana Cavalry (6 coys) was 374 PFD (Freiheit, Boots and Saddles, pg 465). In round figures ca. 3,300 cavalry would be under Pleasanton on the 17th by this measure, but it is probably an overestimate since there would have been continual losses of horses etc.


The 4,543 PFD in the 20th September return thus adds approximately 1,250 to this number. McClellan reduced it to 4,320 by removing the 1st US and hence Pleasanton has gained at least 1,000 men. If the general losses of horses etc. are in the hundreds then the 6th US, 8th Pa and horse artillery can fit in here.

On the 20th September return, the 3rd Pennsylvania (and possibly the 8th New York) are likely carried under the 1st Corps, and the 6th NY under the 9th Corps. The detached 1st NY and 12th Pennsylvania are likely not included on this report, as they have not apparently submitted muster reports etc., although the battalion of the 12th Pa with Sumner have have reported there.

On 1st October, the AQMG reported the 14 regiments of cavalry with the army had an estimated 7,000 cavalry horses and 640 artillery horses, along with 600 horses and 780 mules with their vehicles. This fits the 7,621 present on 20th October. Defining "14 cavalry regiments" is helpful, because it means that it must include the 6th NY Cavalry from the 9th Corps (which has 217 horses, which is about correct for the 5 small coys of cavalry escorts) and the 12th Illinois. This gives a rough average strength of 500 horses per regiment.

Pleasanton made no returns on the 30th September or the 10th October (in the OR returns the cavalry entry is a repeat of the 20th September), but by the 20th October Buford had recovered enough to assume command of the division and he reported 6,724 PFD, explicitly including the horse artillery. This increase of nearly 2,200, seems to be the missing regiments. The grand aggregate has increased 10,911, an additional 3,225 on the rolls. This would equate to about 36 or 38 extra coys, i.e. the three detached regiments (36 coys). On the 21st October the 8th NY was formally added to the Cavalry Division, and the return likely doesn't include it. Hence the three extra regiments are the 3rd Pa, 1st NY and 8th Pa, all of which were always part of the Cavalry Division, but detached. The 8th NY, 12th Illinois and 12th Pa would be reported under "Defences of the Upper Potomac".

Some will criticise McClellan for providing small escorts to HQ's, despite this being utterly necessary. The strengths of the escorts were roughly:

  • Army HQ: 147 (Freiheit, 454)
  • Provost (2nd US and McClellan Dragoons): 164 (Freiheit, 466-7)
  • 1st Corps: 158 (from ORA1, 19(1), 97 with horses converted to PFD at 88%)
  • 2nd Corps: 109 (Freiheit, 455)
  • 5th Corps: 92 (Freiheit, 455)
  • 6th Corps: 140 (at 25% August regimental strength of 6th Pa)
  • 9th Corps: 191 (as 1st Corps)
  • 12th Corps: 67 (as 1st Corps)
    • Sum = 1,068
Whilst this is the equivalent of a full strength regiment, it is certainly not excessive. The allowance is essentially a squadron per corps which is the generally accepted necessary strength assigned to an HQ.

Hence in general terms, the probable strength in round figures on the 17th, allowing for 10% straggling (consistent with the infantry) and losses of horses was:

  • Pleasanton: 3,000 (6 regts) and 18 guns manned by ca. 360 men
  • Flankers; 3rd Pennsylvania, 6th NY (2 Bns) and 12th Pa (1 Bn): ca. 1,000
  • Various escorts: 1,000
    • ca 5,000 cavalry on the field, all up.
  • McReynolds' Expedition: 1,800 (assuming 12th Pa "average")
  • 1st US: 223 (led the 6th Corps in)
  • 6th US: 470 (at Maryland Heights)
    • ca. 2,500 cavalry belong to the AoP not on the field
  • Voss' Brigade: 1,600 at Greencastle of whom 8th NY (ca. 600) ride down to join at Antietam late on the 17th. (Freiheit, 456)
Conclusions

The errors in the OR orbat can lead people to make incorrect conclusions. In knowing the orbat as it was on the 17th, and the strengths, more correct conclusions can be made.

McClellan did not have an excessive dispersion of cavalry to escorts etc., but rather about the minimal number to make things work. McClellan also placed relatively light cavalry screens on the flanks.

Pleasanton had dispatched a large body of cavalry, about a third of his cavalry, in an expedition to chase down Fitz Lee's Brigade. This was likely a necessary task given the threat of leaving a large body of cavalry threatening his rear. Unfortunately they didn't catch Fitz Lee and weren't available on the 17th.

Pleasanton had the bulk of his available cavalry, six regiments and 18 guns, massed as per doctrine. This was a good use of cavalry. They crossed the Antietam at 1000 hrs and bombarded the enemy with the horse artillery. It is clear from McClellan's communications with Pleasanton that they were to charge if an opportunity presented itself. Their position was such that they could take the Sunken Road in the flank (and the horse artillery had enfilade fire down the Sunken Road). It is perhaps a shame that Pleasanton decided to hold the cavalry back, but understandable.

McClellan had less cavalry available at Antietam, but had more on the campaign. He had about 6,500 cavalry excluding escorts to deploy vs ca. 5,200 for Lee (Freiheit, 457). However, McClellan had to cover more poissibilities, and hence the 6th US and McReynolds' expedition were not on the field on the 17th.

Some criticism may be made of McReynolds' absence, but sending the expedition in that strength was clearly the right thing to do. The criticism mostly lies with McReynolds, who once it was clear he wasn't going to catch Fitz Lee turned around and headed back to Frederick rather than turning SW towards where the army was heading. Had he shown more initiative he would have arrived at the field on the 16th. Similarly, Voss' brigade could have arrived at Jones' crossroads with Davis' 8th NY on the 16th rather than the 19th. Had McReynolds and Voss acted with initiative McClellan's usable cavalry force at Antietam would roughly have doubled. This would likely have impacted the battle in a positive manner. Clearly McClellan's judgement of July that McReynolds was unsuitable to command a brigade was the right one.

Whilst unfortunate that McReynolds and Voss would miss the battle, it is clear that McClellan did a good job with what cavalry he had. Had he had a corps of 13,000 cavalry instead of 6,500 (i.e. the strength Hooker, Meade etc. had) then he'd have been able to do more with it. However, even more critical is that his best cavalry leaders (Averell, Gregg and Buford) were sick or wounded. Averell and Gregg would have been McClellan's choices to command the brigades, and had Gregg been commanding the expedition to Gettysburg rather than McReynolds, no doubt he'd have gotten to Antietam.

The cavalry of the Army of the Potomac would double in strength in the next six months, and Averell, Gregg and Buford would return to active services. McReynolds would be gotten rid of. Things would improve. It is a shame that the cavalry was allowed to get so run down in August '62, narrowing McClellan's options.
 
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