Wednesday, 2 September 2015

British Measures of Strength - Winter 1854-5

In a recent discussion on the ever opinionated TFSmith121 had an unfortunate bout of research failure. He threw in some extremely inaccurate numbers for the British Army of the East. Maybe it's worth examining how British returns are filled in.

Here is a link to the actual morning states of the British on various days in the winter of 1854-5 (ref), and here is the data in a nice modern table (click to embiggen), with the same numbers processed into the Federal US equivalents:

(NB: Numbers exclude a brigade of Royal Marines who were at Balaklava with 2nd (Highland) Brigade, 1st Division)

Note the British have more strength categories, and if we'd had some different tables they'd also separate out those Present Under Arms (PUA) into those detailed to the trenches and those available for other duties. We might also separate those "on command" (roughly "extra duty" in US terms), Bâtmen and other employees (roughly "special duty" and "daily duty").

The strength PUA is those available to fight, rather than on other duties. When we read strengths in many British Napoleonic and other histories (like Oman's magnum opus) the "effective strength present" is the total of officers and men PUA, excluding men "on command", sick etc. - see here for an example of Sir John Moore's Army of 1808 (ref). This leads to a distortion, because French strengths are generally reported as roughly "present for duty" and a distortion in favour of British fighting prowess occurs similar to US-CS distortions.

So what of Smith's claim that the British only had 8,000 troops actually present, ignoring the fact that he called the 1st (Guards) Brigade, 1st Division the "Guards Division" and completely missed out the largest division in the army (Light Division)? Simple - he's ignorant of the fact that these numbers, which are perfectly valid and derive ultimately from Kingslake Vol. 6 (ref) are only that portion of the army actually engaged (excluding the Light Division).

Anyone who'd read any regimental histories (or Kingslake) would know that Inkerman was fought by those portions of regiments not assigned to the trenches. Take the 88th Foot (The Connaught Rangers) for example marched to Inkerman with the Grenadier, No. 5, No. 7 and Light companies, and were joined late in the battle by No. 2 company after they'd been relieved by No. 3 company (ref); No.s 1, 4, 6 and 8 companies were on trench duty. The four companies that set out mustered only about 290 men, but this implies 725 effectives in the battalion as a whole. There were 31.2 battalions of infantry (exc/ Marines) with the army and the 3rd November morning state shows 18,498 infantry officers and men PUA for an average of 593 - the 88th may have been a strong battalion, although it is not clear the returns above include the detachment at Balaklava.

As one should note, the total present increased even though the combat strength stayed static due to illness. There was a steady flow of replacements to the old regiments, but 12 full battalions (the equivalent of a full infantry Corps de Armee in 1862 terms) reinforced during the period*.

Here we can see the British had far more sensible measures of strength, but stulti caveant for those who don't understand it!

* Arrival dates:
12th Nov - 62nd from Malta
20th Nov - 97th from Greece
27th Nov - 9th from Malta
4th Dec - 90th from England
9th Dec - 34th from Corfu
15th Dec - 17th from Gibraltar
19th Dec - 89th from Gibraltar
22nd Dec - det. 71st from Corfu
26th Dec - 18th from England
1st Jan - 39th from Corfu
19th Jan - 14th from Malta
3rd Feb - remainder 71st

Tuesday, 25 August 2015

Map: McClellan's Last Campaign

Since I've just got a scan from the Library of Congress of the position of McClellan's army when he was relieved I'll put it up here for future reference. Click to expand.

Sunday, 2 August 2015

Effective vs Present for Duty (1): Army of Northern Virginia

1. Introduction

With an army it is obvious not every single soldier is available as a shooter; that's Heinlein's novel Starship Troopers, not history. The question thus is how many of those present and fit were actually shooters.

Non-shooters (excepting the sick and under arrest) typically fall into three categories, which are only really distinguished by time and whether extra pay is due:

Daily Duty: every morning the company would detail a few men in turn to take their turn assisting the cooks, tending fires, guarding the packs of the rest of the company if going into battle etc.. This was a rolling roster and the privates all took turns.
Special Duty: troops assigned to non-line duties who are not due extra pay (typically for stints of less than 10 days). May be cooks, clerks, teamsters, hospital orderlies etc.
Extra Duty: troops assigned to non-line duties who for greater than 10 days and are due an extra 35 cents p.d.; however they are typically doing the same jobs as S.D. troops, but are generally more or less permanently detached from their regiment.

The troops assigned "daily duty" were always carried in the "present for duty" column in all armies, but the "special" and "extra duty" men sometimes were and sometimes weren't. What's more under pre-war regulations only the men on "extra duty" were broken out into a separate column (a consequence of them drawing extra pay), leaving those on "special duty" mixed in with the PFD.

When looking at numbers with reference to trying to determine the number of shooters it is important to know how to read field or monthly returns.

For the Confederates we have quite a lot of information, and it varies by army.

2a. Army of Northern Virginia

Fortunately Taylor was explicit that at the time of Gettysburg all the "special and extra duty" troops were not counted as "present for duty" (ref). The number of "effectives" is approximately synonymous with the combat strength of the army minus temporary detachments like camp guards and officers. By this period "present for duty" was the number of officers and men for battle, and the "effectives" was the same minus officers.

The question is did Lee ever change definitions, and did Johnston use the same ones?

To answer this all available returns of the Army of Northern Virginia in the OR were entered into a spreadsheet, excluding some divisional returns etc. A large gap should be noted for the spring of 1862.

The 23rd April return for Magruder's corps (ref) was awkward, with McLaws reporting his PFD, aggregate present and present and absent as the same number! For ca. 30th April and 20th May Johnston gives us the approximate "effective strength" of his brigades (noting the second is largely a copy of the first). Thus these returns are excluded, leaving 54 returns from the "Army of Northern Virginia" and 6 returns from 1st Corps, Army of the Potomac. PFD is plotted against aggregate present in figure 1.

Figure 1: Scatter plot of "Present for Duty" vs "Aggregate Present" for the Army of Northern Virginia and 1st Corps, Army of the Potomac. Data from Official Records.

The correlation is remarkable. It is clear that at no point did definitions change, which would be apparent by effectively two different series. The one outlier is the 20th July '62 - the first return after the Seven Days. There is a similar (but not significant) deviation immediately after Gettysburg. The best interpretation seems to be either an underreporting of PFD or a significant breakdown in the army (since wounded were sent to the hospitals around Richmond they were "absent"). This implies that after the losses of the Seven Days and detaching Jackson and Ewell back to the valley Lee still had around 80,000 PFD, ca. 10,000 more than he reported.

However, we can observe differences between Johnston and Lee when they report "effective strength". In both cases it approximates PFD, but Johnston included officers and Lee did not. Whether the transition occurred under Lee or whether Johnston dropped officers from effectives after his 28th February report is unknown. Interpreting Johnston's 30th April and 20th May estimate of effectives is thus problematic. In previous work I have assumed Johnston continued to include officers, but there is little to recommend this other than it being the conservative number.

2b. Army of the Peninsula and Norfolk

Magruder's 31st December '61 return has a PFD:Present ratio of 0.79, lower than the norm in Lee's army. Ergo same deal, non-combatants aren't included in the PFD category. Comparing DR Jones' return of 23rd April (which is AP and P&A only) with his "effectives" one week later gives a ratio of 0.83.

The 31st December '61 and 31st January '62 have both ratios of 0.85, in line with Lee. Interestingly Colston's brigade has PFD 147 offrs and 2,752 other ranks, whereas in Johnston's return of 30th April it has 1,750 effectives; this minor mystery was solved by observing that the earlier returns included 46 artillery pieces emplaced along the James river and their crews.

Monday, 20 July 2015

Effective Strength of the Opposing Armies at Yorktown

1. Introduction

Civil War history has a bad habit of comparing apples and oranges when strength categories are in contention. Invariably the "effectives" of the Confederacy is compared with the "present for duty" strength of the Federals. This distorts matters. Here we will adopt the approach of accepting the Confederate measurement and moving the Federal measurement to conform. We will also analyse the arrival times of various units to determine strength ratios.

2a. Confederate Effective Strength and Arrival Times

To determine Confederate strength the partial return Johnston provided ca. 30th April in the OR (ref) is used. To this some cavalry is added from the OR (ref) and Livermore (ref). Steven Newton estimated that between 10 and 20% of the army went sick in the trenches, and thus a correction factor of the lower bound (10%) is used in the sure knowledge this is not overcorrecting.

Arrival dates were ascertained by a general survey of biographies, regimental histories etc., and the last unit to arrive (Pettigrew's brigade) essentially walked the whole way, whilst most units got a train and then a steamer to King's Mill Wharf in Williamsburg. Results are in table 1. The entry "present before campaign" indicates the unit or formation had joined by 5th April, in some cases barely (such as Colston's brigade from Norfolk, and Pendleton's artillery).

Table 1: Effective Strength of Johnston's Army at Yorktown with Arrival Dates

2b. Strength at Various Dates

Accepting Newton's lower bound of 10% and correcting for a constant decay down to the 30th April estimate by Johnston we get the following strength at Yorktown (inc. Gloucester Point, Williamsburg etc.) for various dates:

Table 2: Estimated Effective Strength of the Yorktown Defences at Various Dates

3. Federal Effective Strength

One problem facing us estimating Federal effective strength is what did Johnston mean be "effective strength"? He appears (from previous returns) to be estimating his officers and men that were combat effectives, so that's the measure I will use.

Secondly there is the issue of what constitutes arrival? Do we count Casey, whose division consists of newly raised troops who haven't even been issued tents and so are suffering in camp near Fort Monroe whilst the QMG in Washington sorts his act out and don't move forward to a mile behind the main army on the 11th? When did Hooker, Richardson and Franklin actually arrive?

In his diary entry for 11th April la Comte de Paris states Hooker and Richardson have just arrived at Ship Point and have been held there for the moment. My notes indicate the two divisions completed disembarkment 10th-11th April and were held at Ship Point until 16th, when McClellan decided to adopt "regular approaches". Kearny's brigade of Franklin boards ship on the 17th, with the rest boarding on the 24th as a turning force.

Thus I will count Casey, Hooker and Richardson as arriving on the 11th, Kearny's brigade on the 17th (when they board ship) and the rest of Franklin on the 24th (ditto).

The third problem is the lack of divisional or brigade returns for the period. Hence I will estimate divisions at that fraction of their corps. I will take the corps strength, deduct an estimate for cavalry (800 men per regiment) and artillery (20 men per gun) and assume the infantry effectives are 75% of the residue.

Table 3: Calculation of Infantry Effectives in Each Federal Corps

We shall now calculate effectives by date.

McClellan intended to have a much larger body of cavalry, forming a brigade in each Corps taken to the Peninsula, and a reserve of 2 brigades (ref). He ended up with about 6.5 regiments. This of course had a significant effect. Here it's just left at 6,000 for all cavalry in the absence of better data.

The artillery is rated by number of guns. The strength of the artillery reserve (100 guns) is estimated with the rest. However, one would observe without gaining or losing guns or batteries its strength (PFD) has gone from 2,731 on 31st March to 1,888 on 20th May, or 69% of starting strength. This may be a good indicator of wastage. However, a simple analysis shows essentially no Federal wastage during the Yorktown operations, whilst the later Chickahominy operations show heavy losses.

Table 4: Federal Effectives by Date.

4. Force Ratios and Conclusions

Hopefully this is informative. It should be observed that McClellan's infantry force ratios start out in Grant territory of ca. 2:1, but within a few days is closer to 3:2 and by the late siege (with Franklin) are nearer 4:3. The Confederates were able to reinforce quicker than the Federals and by the time McClellan committed to regular approaches the infantry ratio was 4:3.

The question must remain was an immediate attack possible? It might have been, and McClellan actually ordered it. When Keyes reported Smith had met resistance at Lee's Mills his order to the courier bringing the news was “Ride back as fast as you can, and tell General Keyes to attack with all his force if only with the bayonet.”; he had just ordered Porter (leading the other column) “Attack with all your forces as soon as you arrive.”

However, the Confederates laid down such a wall of artillery fire that they smothered the advancing Federals, who settled down to counterbattery, and of course lost because the Confederates had works. The infantry found the approaches barricaded and covered by heavy fire.

Anyone criticising McClellan must provide a viable means of assaulting Yorktown. Personally I believe that after the failure of the navy McClellan hit upon the only viable plan - construct our own works and being up big guns to blast them out and get my infantry across the killing area. The assault was set for the 5th May, with six divisions assaulting the Yorktown fortifications above the Warwick river, but the rebels skedaddled even as the Federal assault forces were moving into their assembly areas awaiting the crossing of the LD.  However I'm open to better options....

Friday, 3 July 2015

Post-Seven Days Reinforcements for McClellan and Strength of the Army at Harrison's Landing

1. Introduction

As the Seven Days broke it dawned upon Stanton and Lincoln that McClellan's attempts to gain reinforcements might have been a good idea after all. They immediately ordered eight regiments from Shields' division, Department of the Rappahanock (then being merged into Pope's Army) to Fort Monroe and the 32nd Massachusetts from Washington was already under orders for Fort Monroe and was sent from the Dept. of Virginia to Harrisons.

Other reinforcements were ordered to Fort Monroe. Halleck refused his orders to send 25,000 (and a slimmed down request for 10,000) and in response to orders for 10,000 each to move from Hunter's and Burnside's departments 18 infantry regiments (6 from Hunter, 12 from Burnside) arrive by 15th July. Washington told McClellan to expect 41,000 reinforcements soon (ref).

Hunter's response was to send six regiments and promise another four when transports arrive, satisfying the request for "10,000" (ref); the initial six sailed on 12th July and a seventh (45th Pa.) on the 18th. Between 30th June and 31st July Hunter's "for duty" strength declined 210 officers and 5,211 men. Given sickness in round figures about 5,000 men were sent to Ft Monroe.

Burnside's 12 regiments were referred to be him as "7,000 infantry" (ref). From his 30th June to 31st July returns the Dept of NC declined by 341 officers and 7,617 men.

Thus by late July (21st when the 45th Pa. arrives) roughly 13,379 officers and men (less sick) were afloat off Fort Monroe.

2. Reinforcements That Reached McClellan

To 2nd Corps:

Kimball's Brigade (from Dept. of Rappahanock)
14th Indiana
4th Ohio
8th Ohio
7th (West) Virginia

This brigade arrived at Harrison's Landing on 4th July and was incorporated as a separate brigade into 2nd Corps.In September McClellan would add two new militia brigades to this one to make French's division that fought at Antietam.

To 4th Corps:

Ferry's Brigade (from Dept. of Rappahanock)
39th Illinois
13th Indiana
63rd Ohio
67th Ohio

This brigade arrived at Harrison's Landing on 5th July and was incorporated into Peck's Division (ex-Casey's) as a new 3rd brigade, replacing the old one broken up several weeks earlier and the regiment distributed to the remaining two brigades.

To 5th Corps:

32nd Massachusetts

This regiment was sent from the Washington defences and incorporated into Morell's Division.

3. McClellan's Strength ca. 2nd July to 10th August

Strengths are shown in table 1. In the immediate aftermath of the Seven Days McClellan had less than 50,000 infantry effectives. On that very day he estimated he didn't even have 50,000 with the Colours (ref)' he was right. In fact this may be an overestimate because a lot of men would have became separated from their units and come in during the next few days.

With the arrival of the nine reinforcing regiments (and some reorg.) McClellan's effective infantry strength swells to ca. 55,000 effectives, and whats more it stays there - equilibrium must have been reached and the camp very healthy. The minor increase is statistically caused by return of lost guns to infantry divisions. This is in direct contrast to Keyes' pleas for withdrawal (ref).

Table 1: Infantry Effectives on 2nd July (calculated by effectives 26th June - reported casualties, before any reorganisation) and on 10th July and 10th August (from OR 11(3) 312 and 367 calculated as before).

4. Effects on the Remaining Campaign

McClellan is significantly weaker in July than he was ca. 20th-26th June. In fact his infantry is about where it was before McCall's division arrived, even after the 9 extra regiments have arrived (ca. 55,000). Thus it only stands to reason an extra ca. 9,600 effectives afloat at Fort Monroe would have been useful, raising McClellan's strength to ca. 65,000 infantry effectives. Lee's returns for 20th July indicate his infantry divisions had ca. 58,579 enlisted men for duty (including artillery, est. 55-56,000 excluding the gunners)) after detaching Jackson and Ewell to the Valley (ca. 13,000 enlisted infantry for duty by August reports). This report would be "effectives" - consider that according the Jubal Early (who was lowballing the rebel strength) Lee had only 80,000 "effectives" and of course lost just over 20,000 (but gained Martin's brigade and some loose regiments, and apparently another draught of conscripts from outside Virginia).**

Thus the numbers haven't really moved. Even after detaching Jackson, Lee has roughly parity in infantry to McClellan, and superiority in late July. Partially this is because despite suffering heavier casualties Lee starts with a slightly larger army and has received more reinforcements.

If McClellan advanced Lee intended on recalling Jackson and calling in French giving him maybe some 68-69,000 effective infantry vs McClellan's 55,000. This indicates a major failure on Washington's behalf; even with Burnside's 9,600 effectives McClellan might still only have parity/ be slightly outnumbered.

This of course justifies McClellan's continual calls with 20-30,000 more effective men. That's actually a conservative estimate of what was necessary. To get ca. 2:1 advantage (like Grant had in 1864) Washington would need to do what it did in 1864 - strip the Valley and more!

5. Conclusion

The summer of 1862 was when the Confederacy was relatively at its strongest compared to the Union, and the numbers on the James reflect this. McClellan's army simply was undermanned for the task it was to undertake against the strength of the enemy. McClellan's requests for reinforcements were reasonable and militarily correct.


* Martin's brigade joined on the 5th July. Evans' and Drayton's brigades had been ordered to Lee but had not arrived before the 20th. Several additional regiments joined with the 44th Alabama and 48th Georgia being incorporated before the 20th (and counted), and the 47th and 48th Alabama***, and the 5th and 8th Florida arriving after the 20th. The listed strengths exclude French's brigade in North Carolina of ca. 1,300 effectives.

** A better way to approach this is from PFD, and with Martin and the new regiments, and deduct Seven Days casualties, giving ca. 96-100,000 PFD, then deduct the garrison of Richmond (10,000) and Jackson and Ewell (15,000) you get ca. 75,000 PFD with equates to ca. 56,000 effectives. Thus either Lee's army has severely shrunk since the Seven Days or he is reporting "effectives".

*** The 23rd July organisation chart (ref) indicates the 47th and 48th Alabama were incorporated into the 3rd brigade of Jackson's division by that date, so they may have arrived earlier but aren't counted in Lee's field return, which excludes Jackson and Ewell, plus attached cavalry etc..

Also note the following (not exhaustive) changes since the Seven Days:

16th Mississippi from "7th brigade", Ewell to Featherston's brigade, Longstreet (creating an all Mississippi bde)
2nd Virginia Heavy Artillery from Pender (as 22nd Va Bn) to Field's bde, both AP Hill
2nd Arkansas Bn consolidated with 3rd Arkansas Regt
4th Georgia transferred from Wright's Bde (Huger) to Ripley's Bde (DH Hill)
Wise's Bde incorporated into DH Hill's division as 6th Bde
 -  Wise has gained 20th Virginia and 59th Virginia, but in fact both of these were incomplete and probably actually with Wise during the Seven Days, but not numerically counted.
4th Georgia moved from Wright's Bde (Huger) to Ripley's bde (DH Hill)
48th NC from Ransom to Walker
Daniel has gained 32nd NC and 53rd NC.
Martin's bde of 4 regts (17th NC, 44th NC, 47th NC, 52nd NC) has joined
DH Hill's "unattached troops" are the 61st Virginia (6th in the OR, typo) and 13th Virginia Cav.

In summary Lee has gained since the Seven Days ended:
  1. 44th Alabama (arrived during Seven Days)
  2. 48th Georgia (arrived during Seven Days, Rafuse or his reference confuses the 48th Ga with the 52nd)
  3. 47th Alabama (join between 20th and 23rd)
  4. 48th Alabama (ditto)
  5. 20th Virginia (incomplete)
  6. 59th Virginia (incomplete)
  7. 32nd North Carolina
  8. 53rd North Carolina
  9. 17th North Carolina
  10. 44th North Carolina
  11. 47th North Carolina
  12. 52nd North Carolina
  13. 61st Virginia
  14. 13th Virginia Cavalry
With en route:
  1. 5th Florida
  2. 8th Florida 
  3. 17th South Carolina (Evans)****
  4. 18th South Carolina (ditto)
  5. 22nd South Carolina (ditto)
  6. 23rd South Carolina (ditto)
  7. Holcombe Legion (ditto)
  8. 50th Georgia (Drayton)
  9. 51st Georgia (ditto)
  10. 15th South Carolina (ditto)
  11. 3rd SC Bn (ditto)
  12. Phillips Legion (ditto)
**** Evans and Drayton joined on 28th July (ref).

Sunday, 28 June 2015

The Effective Strength of the Federal Army in the Seven Days

1. Introduction

The Lost Cause spilled a lot of ink on their weakness in numbers (DH Hill summarised their arguments). Their numbers for the Peninsula Campaign and the Seven Days in particular are invariably their "effective strength" excluding officers and extra duty men. This will attempt to estimate Federal strength the same way as the Rebels got their 80-90,000 strength.

Taking the averages of several estimates of strength by the rebels they typically estimate their infantry at 75% of PFD, artillery at 90% of PFD and cavalry at 60% of PFD. These numbers are applied here to the Federals.

2a. Infantry Effectives

To determine infantry effectives first the 20th June 1862 return is taken and the number of enlisted PFD for each division is taken. This is converted to PFD on 26th by the methodology of Burton (-2.5% or -0.5% per day). The attached artillery is deducted at 20 men per gun to yield the number of enlisted infantrymen for duty on the 26th June. The number of "extra duty" men is estimated at 25% of PFD and thus deducted, yielding ca. 63,000 "effectives" (table 1).

Taking other measures give slightly larger numbers. Including officers (rather than adding separately as in 2d) would give ca. 66,000, and decreasing the extra duty to 20% gives ca. 67,300 without officers (70,500 with).

Table 1: Number of Effective Infantry Present on 26th June 1862 (Click to Expand)

 2b. Artillery Effectives

It is assumed that the artillery has only 10% extra duty men.
Table 2: Number of Artillery Effectives on 26th June 1862

2c. Cavalry Effectives

The cavalry has a larger extra duty element than the infantry, and effectives are rated at 60% of PFD.

Table 3: Number of Cavalry Effectives on 26th June 1862

2d. Total Effectives

The result of tables 1-3 plus officers (at 97.5% of PFD on 20th June) is summarised in table 4.
Table 4:  Number of Effectives on 26th June, Officers Added

3. Conclusions

The late Joseph Harsh estimated 70,000 Federal effectives if the Confederates had about 80,000 effectives as they claimed. Since the rebel estimates typically exclude officers (and some of their artillery) then doing the same for the Federals indeed is around 70,000.

Tuesday, 23 June 2015

The strength an organisation of the Department of Virginia - June 1862

Over on Prof. Brooks D. Simpson's blog Mr. J.F. Esq. (not a doctor) has made an interesting, but confused post about McClellan's reinforcements around the time of the Seven Days. I thought I'd do some digging, and found that no-one knows the organisation of Dix's command. Here's the findings in rough form.

1. Strength and Organisation of the Department of Virginia and Reinforcements for the Army of the Potomac

Any fool can turn to the OR compiled returns for the 20th June 1862 and point to Dix's department and say "there's another division". Of course to do so reveals a certain lack of knowledge and understanding.

When the Department was transferred back to McClellan's command in early June the first thing McClellan did was levy it for every available disposable regiment (and got a few from Washington and Baltimore). Thus twelve regiments were transferred thus:

From Department of Virginia directly:

20th Ind. - to Hooker
16th Mass. - to Kearny
29th Mass. - to Richardson
1st Mich. - to Morell
1st NY - to Kearny
2nd NY - to Hooker
7th NY - to Richardson
10th NY - to Sykes
20th NY - to Smith

From Baltimore and Washington:
2nd Delaware - to Richardson
101st NY - to Kearny
99th Penn. - to Kearny

Incidently, Jubal Early stated this never happened, so of course it did. (ref) The increases in McClellan's strength after Fair Oaks are obvious in increases in the grand aggregate of McClellan's infantry from the 31st May to 20th June returns thus:

2nd Corps: + 2,049 (3 regts)
3rd Corps: + 4,192 (6 regts)
4th Corps: - 190 (no new regts, this represents wastage)
5th Corps: + 654 (2 regts, but the 1st CT heavy arty shifts category taking 6-700 over to artillery)
6th Corps: +666 (1 regt)

Additionally the 11th NY of the Dept of Va was done year regiment and returned home to muster out in this time, removing 10 infantry regiments in total of the Dept of Va. As compensation six regiments were sent to Dix:

3rd NY - from Baltimore
4th NY - from Baltimore
8th NY State Militia - newly embodied
13th NY State Militia - from Baltimore (3 months militia)
25th NY State Militia - new embodied 3 months militia (6 coys only)
19th Wisc. - newly raised

When McClellan was given authority over the Dept of Va he extended it to include Yorktown, Gloucester and Williamsburg, giving Dix the garrisons of those places (such as the "Infans Perdu" battalion). Thus with his existing regiments Dix felt himself very undermanned, giving his breakdown of forces (in aggregate present and absent) thus on the 26th June (ref, I'll include regiments):

* Fort Monroe: 300 artillery "armed only with sabres" (2nd and 4th Wisconsin Batteries), 222  infantry (a few companies of 99th NY)
* Camp Hamilton and Hampton: 1,819 infantry (5th Maryland and the rest of 99th NY) and 90 cavalry (a coy of 11th Pa. Cav.)
* Ft Wool and Sewell's Point: 254 infantry (a few coys of 99th NY)
* Norfolk and Portsmouth: 2,254 infantry (1st Delaware, 19th Wisconsin and 58th Pa.), 309 mounted rifles (1st NY Mounted Rifles) and 80 artillery (Bty D, 4th US)
* Suffolk: 2,769 infantry (13th NYSM, 25th NYSM, 3rd NY and 4th NY), 134 artillery (Bty L, 4th US), 412 cavalry (a battalion of the 11th Pa. Cav.)
* Yorktown and Gloucester: 1,319 infantry (8th NYSM and NY Independent Bn "Enfans Perdu") and 355 cavalry (3 coys of 11th Pa. Cav.)
* Williamsburg: 466 cavalry (battalion of 11th Pa. Cav.)
* Newport News: 84 cavalry and 144 artillery (7th Mass. Bty)

Hence despite losing ten regiments, Dix's grand aggregate only went down by ca. 3,000 due to the gaining of six regiments, a battalion, and possibly some of McClellan's cavalry.

2. Is this a "spare division" McClellan could have used?

Short answer - no.

Dix's command had very little in the way of a disposable force that could have been sent to aid McClellan. His only contribution was to send company I, 99th NY on a steamer that got ground (see the commanders report).

Perhaps Dix could have formed a brigade out of his four reliable regiments (1st Del., 3rd NY, 4th NY and 58th Pa.) but there was no transport available on the river (McClellan called in all transport to move supplies from the Pamunkey to the James), and indeed nowhere to go except White House Landing which is being evacuated. So that's a no-go.

Maybe they can march up the Peninsula, but then they need to be shipped across the James River and then march some 80 miles to reach McClellan's army. Not exactly a rapid reinforcement is it?

Indeed consider the consequences of effectively abandoning Norfolk and Suffolk when the Confederates still have a couple of brigades in NC spare to retake them that Lee kept out of the Seven Days and so aren't ever counted (that's French's brigade and Martin's Brigade). Dix's concerns for the position he'd been put in by the ill-considered occupation of Norfolk weren't baseless.

3. Conclusions

Apart from incomplete orbats that have been filled in, this article basically concludes that obviously a bunch of tied down troops 80 miles from Richmond with no way of getting there could only be counted as "available to McClellan" by someone with incomplete understanding. Even Jubal Early (op. cit.) refrained from such an obviously silly argument. Hence my continual amazement at finding old Jube a more impartial commentator than some alive two centuries later. Next up, old Jube on "effectives" and making an "apple-apple" comparison using old Jube as one of the apples!