What If: McClellan had recieved McDowell?

[Saphroneth]

During the Peninsular Campaign, McClellan called for reinforcements as he advanced up the Peninsula (both before and after breaking through the Warwick line). The reinforcements he was after were specifically McDowell's corps, originally attached to his command, before being removed once he reached the Peninsula and before McDowell's corps had been sent.

In May Lincoln went on a fact finding expedition to the Peninsula, with Seward, Chase and Tucker going ashore to examine the situation and see if McClellan really needed reinforcements. That produced this letter:


Providence Forge, May 14, 1862

ABRAHAM LINCOLN, President

We think that you should order whole or major part of General McDowell's, with Shields, up the York River as soon as possible, and order Whyman's flotilla up the James River. General McClellan moves to White House tomorrow morning.

WM H. SEWARD


In this, McDowell concurred, as did most of the military men to whom the question was put.


Historically, a small part of McDowell's command (one division - McCall, three infantry brigades) was sent to McClellan by sea in June. The remaining troops (three divisions - King, Ord and Shields - plus some loose brigades, totalling 12 infantry brigades) was promised to McClellan by land, but never arrived.


So, the question is - what if McDowell's command (whole, or major part - i.e. at least ten of the fifteen infantry brigades available, if not more) had been sent up the York river "as soon as possible" to join McClellan's army?

 

[Saphroneth]

To provide some hard numbers, the report of May 1862 of the Dept. of the Rappahannock gives McDowell's total strength at 44,450 officers and men Present For Duty (with 86 guns). Of these, 11,200 were sent (McCall's division), with 22 guns.

If we assume that instead the strength sent was "major part", meaning McCall, Shields and Ricketts, plus Geary's brigade, (and the cavalry brigade, as McClellan was very short) this would mean the total sent was instead 34,600, with 80 guns. (This leaves Doubleday's brigade and King's division to watch the line of the Rappahannock, if needed.)

As a consequence, and assuming everything else up to the Seven Days happened on schedule (including the recall of the Valley forces), then the PFD strength of McClellan's force would be 23,400 PFD stronger and he'd have another 58 guns too.

The historical PFD balance as of the Seven Days was roughly (Confederate numbers from Harsh):

104,000 total Army of the Potomac

Confederates:
112,000 total
45,000 in attacking column north of the Chickahominy
22,000 in Army of the Valley
45,000 total defensive forces south of the Chickahominy

Here it would be 127,400:112,000.


One immediate result of McDowell arriving complete is that McClellan's force would total about 127,500. This would be large enough that the Army of the Valley could not be risked away from Richmond, thus preventing any further threat to Washington - indeed, the Valley Campaigns probably don't happen period.

 

[Andy Cardinal]

I guess I'm having trouble picturing this since my knowledge of this is not what I would like. I have always considered McDowell's arrival while McClellan was at Yorktown, or moving overland south from Fredricksburg in June, but not this scenario. I guess my first question is, how long would it have taken for McDowell's corps to board steamers & move up the York? The Pennsylvania Reserves (who were sent) did not reach their positions near the Chickahominy until late June, if I remember correctly? I'm guessing the rest of the corps wouldn't have reached the front any sooner.

 

[NedBaldwin]

This would be large enough that the Army of the Valley could not be risked away from Richmond, thus preventing any further threat to Washington - indeed, the Valley Campaigns probably don't happen period.

I think this is presumptuous. The opportunity for Jackson to run amok would be even greater.

Seward sends his message May 14. Jackson has already attacked Fremont's forces west of the valley and would soon be heading back to the valley to join Ewell to attack Banks. So the valley campaign would still happen.

Lets say Lincoln gives the ok after getting Seward's message. Boats are collected at Alexandria and Aquia to pick up say McCall at Aquia and Ord at Alexandria while still waiting for Sheilds to finish his cross country journey. What would Lincoln et al, do when Jackson/Ewell attack Banks? Would they let McDowell continue to leave?

How long would it take to get the boats together, get the divisions loaded and moved them down the Potomac, down the bay
and up the York?

 

[Saphroneth]

I guess I'm having trouble picturing this since my knowledge of this is not what I would like. I have always considered McDowell's arrival while McClellan was at Yorktown, or moving overland south from Fredricksburg in June, but not this scenario.

Odd, isn't it, since this scenario is what just about everyone except Lincoln and Stanton thought was a good idea.

I guess my first question is, how long would it have taken for McDowell's corps to board steamers & move up the York?

Essentially it depends how many transports are made available - the more there are, the faster the process is. Since it's an "administrative move" (troops going from friendly port to friendly port) they don't have to travel in a body and they don't need escorts.
If they commit to the decision to send the troops on or about the 14th, they should be able to catch the transports that were used for the Eltham's Landing operation, at least, which was enough vessels to move a full division at once. That would be able to move the infantry and artillery component in no more than three lifts, with the cavalry possibly taking a separate one, which suggests the infantry component of the force should have arrived after about two weeks.
Historically McCall wasn't sent for at least another week or two, and that may be why they seem to have lost track of Franklin's transports.

I think this is presumptuous. The opportunity for Jackson to run amok would be even greater.

Seward sends his message May 14. Jackson has already attacked Fremont's forces west of the valley and would soon be heading back to the valley to join Ewell to attack Banks. So the valley campaign would still happen.

You're right, my apologies, the first Valley campaign could still happen. If the movement takes place, however, the second Valley campaign would be impossible - and it's also not impossible that if the force transfer happens quickly enough Jackson's pulled back to Richmond, as he didn't battle Banks until the 23rd and by then force transfer could easily have started.

Lets say Lincoln gives the ok after getting Seward's message. Boats are collected at Alexandria and Aquia to pick up say McCall at Aquia and Ord at Alexandria while still waiting for Sheilds to finish his cross country journey. What would Lincoln et al, do when Jackson/Ewell attack Banks? Would they let McDowell continue to leave?

Well, we know what happened historically, which is that Jackson attacked Banks and panicked Lincoln and Stanton into freezing the (overland) movement order. This was exactly what Jackson's valley campaign was intended to do.
In this hypothetical, meanwhile, either they don't panic (e.g. they pull the Valley forces back up the Valley in a defensive posture) or they remain committed to the over-water movement and thus after the scare has died down they can move everyone over to McClellan very quickly (having been gathering transports for another few weeks).

Note that when I say it panicked Lincoln and Stanton, that's because they're the only people involved in command decisions here who really were. McDowell and Scott, among others, strongly held that McClellan should get the reinforements they'd said were on the way. Essentially this what-if is "what if Lincoln and Stanton took the advice of their military and civilian advisors on this topic, instead of asking for advice and then ignoring it?"


On a fundamental level, here, giving up much of the Valley on a temporary basis doesn't matter. Even giving up the Rappahanock line on a temporary basis doesn't matter, if it's really not possible to move troops from Halleck's enormous army into the east to replace those promised to McClellan - there's no way to actually threaten Washington, not unless Lee wants to completely abandon Richmond to McClellan's tender mercies, and once Richmond is taken then the Confederates have to withdraw from basically the entirety of Virginia.

 

[67th Tigers]

In mid-May the "Army of the North" and the "Department of the Appomattox" still exist.

The former of these will become AP Hill's grand division (i.e. Corps) by the end of the month when they're reassigned to Johnston, who pulls them back to Richmond.

Ewell's division was at Gordonsville and was in a situation of strategic paralysis. Lee, who was coordinating movements, wanted Ewell's division to move on Fredericksburg, join the Army of the North (and take over as commander), and then strike McDowell. He'd have at least 8-9 brigades of infantry and around 20,000 effectives if no more pried from elsewhere. However, Jackson's escapades in making a spoiling attack against Fremont's advance over Allegheny Mountain and intelligence Shields was going to leave the Shenandoah, had halted that. Ewell had to be ready to try and intercept Shields, which was Jackson's job, but Jackson had launched himself on a pointless movement against McDowell.

The int that Shields was going to Fredericksburg was correct. On 10th May Shields and a brigade from Williams were ordered to reinforce McDowell, and they started marching on the 12th, arriving on the 21st.

On the 14th May Jackson signaled with was going to return to the valley. Johnston gave Jackson and Ewell orders to either strike Banks or, if Banks withdrew to a defensive position and sent Shields away, to march east, unite with the Army of the North and strike McDowell if he marches south.

On the 18th May Ewell rode through the night to meet Jackson. They had received two contradictory sets of orders. One from RE Lee suggested they unite and attack the rump of Banks' force, and the other from Johnston said Ewell should move to oppose McDowell at Fredericksburg. He chose the former to obey. Branch however obeyed the order from Johnston (issued immediately the AotN was placed under his authority) to withdraw to Hanover Court House and cover the withdrawal of JR Anderson's and Ewell's divisions to Richmond. McClellan's movement had turned Richmond and made the Army of the North's position (including Ewell's) untenable. Of course OTL Ewell didn't do as he was told and remained in the Shenandoah.

ITTL With Shields going as well, Ewell will also be recalled to Richmond in late May. Jackson will be too weak to threaten Williams. Historically in his 18th May meeting with Ewell he said he was not capable of striking Williams without Ewell. Even if things develop as historically in late May, then Jackson will not be in a position to attack Harper's Ferry defended by 3 divisions (Williams', Blenker's and Sigel's). If he hangs around the upper valley he's exposed and can't move to defend Richmond. Common sense would see him withdraw.

With McDowell arriving at White Oak Landing with 4 divisions late May/ early June then nothing can stop McClellan. The question we have to ask ourselves is when Richmond falls, early July or late July. McClellan had already committed to a series of "bite and hold" attacks, the first two of which (Oak Grove on 25th June and Garnett's Hill on 26th) historically happened. McClellan would inexorably grind through the rebel defences over the coming weeks. The only thing that could prevent this is destroying his supply base, but now they're defended by some 7 divisions.

 

[NedBaldwin]

it's also not impossible that if the force transfer happens quickly enough Jackson's pulled back to Richmond, as he didn't battle Banks until the 23rd and by then force transfer could easily have started.

Force transfers were what motivated Richmond to direct Jackson to attack and not to pull back. So I dont see what you suggest as the likley outcome. In the actual time line Sheilds was moving to unite with McDowell to move overland. The difference you suggest is that the move be made by water. By the time Jackson/Ewell would have learned anything was different, they would be attack Banks anyway. The important difference in your scenario is that hope that Lincoln/Stanton would not panic and would not halt McDowell as a result. So let say they didnt. Banks retreats to Maryland, Jackson/Ewell roam around the Valley, move into Loundon/Manassas area, cause havoc, break rail lines, probably route Geary... but ...but ... they are really more of a nuisance than anything else. If Lincoln and Stanton can stay calm, they can ignore the temporary losses and focus on moving McDowell without serious problem to the war effort.

So then the question is given he would start June with 3 more divisions than he historically did, how does McClellan fare differently. Does he continue to advance along the rail line or does he go for the James? If for the James does he end up in a better spot than Harrison Landing? And what then? Im really not sure the answers but I think it is fanciful to assume that Richmond falls that summer without more thorough analysis.

 

[Saphroneth]

Force transfers were what motivated Richmond to direct Jackson to attack and not to pull back. So I dont see what you suggest as the likley outcome.

That troops would be withdrawn to Richmond to help protect it - much like how Grant prevented major offensives leaving Richmond by sitting at Petersburg, the greater the threat to Richmond the more it prevents Confederate offensive action. The question is basically whether Ewell is recalled to Richmond.

So then the question is given he would start June with 3 more divisions than he historically did, how does McClellan fare differently. Does he continue to advance along the rail line or does he go for the James? If for the James does he end up in a better spot than Harrison Landing? And what then? Im really not sure the answers but I think it is fanciful to assume that Richmond falls that summer without more thorough analysis.

Well, historically, by the end of June McClellan was conducting attacks to take small areas of ground to use for his battering trains (Oak Grove, Garnetts Hill). The idea here was to work forwards a bit at a time, without leaving the cover of his heavy guns (i.e. use the guns on Garnetts Hill to cover the next assault, then move them up to the ground thus gained etc.) This process is one which Lee concluded he could not defend against (a "battle of posts").
(McClellan hadn't moved earlier for two reasons - he was waiting for McDowell and the ground was too wet to move artillery.)

Historically the only way Lee came up with to get McClellan away from Richmond was to attack his supply line north of the Chickahominy river - the rail line from White House Landing - because McClellan hadn't been able to make that position as strong. In this alternative McClellan has the troops (6-7 divisions) to make the position essentially proof against attack without abandoning Richmond, and he has as many troops south of the Chickahominy as north.

Basically at that point Lee is stuck and cannot prevent the reduction of Richmond. His historical option is gone - he can't attack the supply line - and if he tries a serious attack south of the Chickahominy McClellan's big guns and field fortifications will slaughter him. It's a battle of posts where all the advantages are with the Union (as they have the bigger guns), and as of day one of the Seven Days McClellan was six miles from Richmond city centre. Fort Jackson is three miles from Richmond city centre (and is the main defensive work along the vector McClellan was taking), and once the parallels get within a mile they can reduce the fort.

So to take Richmond by the end of July McClellan needs to advance his lines two miles in a month - or even two months, as with McDowell already there rather than "promised to come in a few days, General" for an entire month he might have been making his advances of lines in June. Since each individual attack can be well supposed by the siege guns (and if there's one thing McClellan was a Union expert at it was using heavy guns to render an enemy position untenable) it shouldn't take too long to advance the lines that far.

 

[67th Tigers]

Force transfers were what motivated Richmond to direct Jackson to attack and not to pull back. So I dont see what you suggest as the likley outcome. In the actual time line Sheilds was moving to unite with McDowell to move overland. The difference you suggest is that the move be made by water. By the time Jackson/Ewell would have learned anything was different, they would be attack Banks anyway. The important difference in your scenario is that hope that Lincoln/Stanton would not panic and would not halt McDowell as a result. So let say they didnt. Banks retreats to Maryland, Jackson/Ewell roam around the Valley, move into Loundon/Manassas area, cause havoc, break rail lines, probably route Geary... but ...but ... they are really more of a nuisance than anything else. If Lincoln and Stanton can stay calm, they can ignore the temporary losses and focus on moving McDowell without serious problem to the war effort.

Logistically Jackson was very overextended. His orders were to mount a demonstration against Harper's Ferry and then come back down the Shenandoah to Brown's Gap, and hence move to Richmond. All the fighting after 25th May was Jackson and Ewell stop punching the divided pursers. It really was an attempt to divert McDowell from McClellan and then unite to strike McClellan.

So then the question is given he would start June with 3 more divisions than he historically did, how does McClellan fare differently. Does he continue to advance along the rail line or does he go for the James? If for the James does he end up in a better spot than Harrison Landing? And what then? Im really not sure the answers but I think it is fanciful to assume that Richmond falls that summer without more thorough analysis.

Stanton's order stands. The base of the army is fixed at White House Landing. McClellan accepted this and intended to grind through the rebel entrenchments. There is only one thing the rebels would do to prevent this - destroy McClellan's supply lines. With McDowell arriving this becomes essentially impossible.

With McDowell I wonder whether McClellan will feel strong enough to directly block the Mechanicsville and Meadow Bridges, in which case Lee is truly "bottled up". However, a look at a topographic map of the area of the Mechanicsville Bridge shows it's pretty indefensible from either side. The rebel line of defence there was well back from the river.

 

[Saphroneth]

Hmm, I might do some mapping stuff on this tomorrow. Possibly even a quick time-line.

Assumptions...

• They use the Eltham's Landing troop transports, which it is assumed take four days for a round-trip to deliver three infantry brigades plus arty.
• Ten (or eleven) infantry brigades are sent, plus their artillery, and the cavalry brigade. This thus takes four complete lifts and gives McClellan McCall, Shields and Ricketts, plus Doubleday's brigade and the cavalry, completing the move on the last day of May.
• Seven Pines still happens.
• There is good enough weather in the second week of June for some combat, though not much.
• The weather clears up around the 24th of June.

 

[Saphroneth]

Map 1: positions before first Federal offensive (taken from the morning map on the first of the Seven Days for positions south of the river)

Union forces south of Chickahominy:


Divisions of Slocum(3), Smith(3), Richardson (3), Sedgwick (3), Couch (3), Peck (2)
Brigades of Carr, Birney, Robinson, Berry, Sickles, Grover

Total brigades 23


North of the Chickahominy

Divisions of Morell (3), Sykes (3), McCall (3), Shields (4), Ricketts (3)
Brigade of Doubleday
Total brigades 17


The south-of-Chickahominy troops and positions are historical for 25 June, though the map is actually for 13 June in this alternate - essentially it's the time when McClellan goes on his first offensive, during a short break in the rains.


As for the Confederates, their force north of the Chickahominy is just the historical Army of the Valley, keeping pressure on the northern Union flank across the Topotonomy. Brigade count:


South of river:

AP Hill (6)
DH Hill (5)
Huger (3)
Longstreet (7)
Jones (2)
Magruder (3)
McLaws (2)

North of river:
Jackson (4)
Ewell (3)
Whiting (2)


Each line is a brigade. A triple line indicates a three-brigade division closed up in line.

 

[Saphroneth]

Actual map...

 

[Saphroneth]

First thing I should note is that the actual positions of the advanced pickets are somewhat forward of the lines - they weren't two miles apart.

My thought on the likely operations is that McClellan will mount two offensives on successive days, first on the south of the line (basically Oak Grove) and the second on the north of the line (Garnett's Hill/Golding's Farm). Then the rain sets in again and McClellan digs in there.

Question is... what does Lee do in this situation?

 

[Saphroneth]

Operations Against Richmond

First Phase (13-15 June)

A dry period in the weather persisted for a few days, which was considered sufficient to begin operations against the Richmond defences - beginning on the 13th of June. The divisions of Hooker and Kearny each contributed brigades to the operation, totalling three brigades (Sickles, Grover, Robinson).
The operation was muddled and confused, chiefly a result of the need to attack over the headwaters of the White Oak, and McClellan's attempt to manage the battle by telegraph was not a success.
Upon arriving on the battlefield around 1PM, McClellan ordered the attack renewed, and sporadic fighting continued until nightfall.

The next day (the 14th), offensive operations took place on the other end of the line. Smith's division was used to take Garnett's Hill and Golding's Farm, both positions near the Chickahominy at about the level of the Foot Bridge and Lower Trestle Bridge. This second operation went somewhat more smoothly, partly because McClellan was present in person rather than managing the battle by telegraph and partly because of a well-timed threat by Lovell's Brigade of a crossing of the New Bridge, which drew off some Confederate forces that would otherwise have been available to reinforce.

Rain was already setting in on the morning of the 15th when a counterattack was launched by elements of D.R. Jones' division against Garnett's Hill, with the result that Hancock's and Brooks' brigades repulsed Toombs' brigade and Griffith's brigade, though not without cost.

The overall casualties for the operational phase were 1,100 Union and 1,000 Confederate, of which about half were "recoverable" casualties (i.e. men lightly wounded who would recover within a few weeks). In addition to this the Union lines were advanced in two places about 1/3 to 1/2 mile towards Richmond, and works were built on the newly taken ground over the next week along with protected gun positions for McClellan's heavy siege guns.


The paucity of the advance drew some jokes in Washington, but in Richmond was cause for greater concern. Once heavy guns were emplaced in the two new positions it would be possible to destroy the works of Huger, McLaws and DR Jones within sight of them, and this would in turn allow another advance; however, attacking McClellan's works would be a costly endeavour.

Perhaps the most vulnerable component of the Union line was the flanks, with the northern flank along Tolopatamony Creek held by five brigades, but Lee's intel suggested another three brigades (the division of Ricketts) were nearby in reserve at Bethesda Court House. The southern flank was about as lightly held, but a swamp was in the way.

Consideration was also given to an attack on the newly advanced position at Oak Grove, as it was not directly connected to the main Union line at all places due to the flooding of the White Oak. (McClellan's engineers were producing a causeway and bridge to make the Oak Grove position more secure, but the work was slow.)

 

[Saphroneth]

It looks like the next objective for McClellan's forces is the Old Tavern area, which should be in range of the guns on Garnett's Hill. That attack would probably be conducted by brigades of Richardson and Smith.
There's also a case for an attack down the rail line (supported by the guns at Oak Grove)

 

[Saphroneth]

I've given some thought to what manoeuvre Lee might make to prevent McClellan pushing forwards, and I think the one which seems the most likely is a variation on an attack en echelon.

The total manpower Lee has to offer at this point is about 116,000 PFD, of which about 40,000 has to stay in Richmond to defend it - that can't really go any lower. But it should be possible to, say, mount attacks as:

Army of the Valley (about 25,000 PFD) - attacks across the mouth of the Tolopatamoy on day one, in the morning.
Stuart (about 2,000 PFD cavalry) - try to get across during Jackson's attack and make for the rail line
DH Hill (about 12,300 PFD) and AP Hill (about 16,400 PFD, though roughly half of this has to stay in the forts) - attacks across the head of the Tolopatamoy and across the Chickahominy via the Meadow Bridge, on the afternoon of day one.
McLaws, DR Jones, Magruder, Holmes (about 24,000 PFD) - stay in the forts, make demonstrations.
Richmond defences proper (about 9,000 PFD) - stay in the forts.
Longstreet (about 14,000 PFD), Huger (about 6,000 PFD), cavalry (about 2,000 PFD) and reserve artillery (about 2,000 PFD) - attack the White Oak bridge, morning on day two
Petersburg defences (about 2,000 PFD) - sally to join Longstreet

The concept of operations here is pretty simple - try to draw McClellan's reserves out by threatening him to the north and then attacking from the south. The aim is to try and ensure that there's insufficient reserves available to meet what is essentially an attack of about 26,000 troops in the south.

The downside of it, of course, is the size of the battlefield - you need to give time in an attack en echelon for reserves to be committed, though the plus side here is that if reserves do get committed in the north it's going to take about a day to move them south again.

If McClellan's subordinate commanders react by pulling in reserves in their immediate area but otherwise just sit in their works, you have:

Seven brigades opposing the Army of the Valley
About seven brigades opposing the Hills' attack
Fifteen brigades opposing the demonstration attacks by the Richmond defences troops
And three brigades spare to march down and reinforce the White Oak bridge against Longstreet's attack

After that you have to start pulling troops out of the line, though fortunately it's quite dense facing Richmond so if McClellan thins it as much as he was willing to historically he can get another three-four brigades out of it easily.

 

[Saphroneth]

So the outcome of those attacks, estimated:

Jackson's attacks. These are dawn attacks against a fairly lightly held but dug-in line on the other side of a creek. It's about 25,000 PFD attacking against 12,000 PFD defending, with another 9,000 defenders about two hours away. Since the creek's muddy but not deep, infantry can cross but artillery has trouble - so my conjecture is that there's pretty desperate fighting for a couple of hours, until the reinforcements arrive and stabilize the situation.
Stuart - makes it across, conducts a raid on the rail line and burns one of the bridges, hasn't got the force to do much more. His attempt on the rail bridge fails.
DH Hill and AP Hill's attacks. Attacks during the day, mostly across more difficult terrain. There's scope for a mini-converging attack here, and it's about an even fight - 21,000 PFD versus 21,000 PFD. No real progress made, but it does draw in the reserve brigade from Walnut Grove and this gets reported as evidence of reinforcements being committed. (Franklin's cool enough that it doesn't strain him - historically he didn't ask for reinforcement until arguably it was too late even when hit by twice this.)
Later on in the day McClellan's cavalry fights an action with Stuart's cavalry, coming off worse but also causing Stuart to retreat across the Tolopatamoy.
Skirmishing continues on the fronts opened earlier on in the day.
Demonstration attacks from the Richmond forts - as per historically these convince most of McClellan's corps commanders they're in trouble. Some casualties take place and the Confederates come off overall the worse, because of the new fortifications - worse, the US Sharpshooters do particularly good work on some of the supporting Confederate artillery.

Longstreet's attack goes well, capturing the bridge over the lower White Oak and pushing back the flank guard brigade. McClellan strips out a total of four brigades from the forces facing Richmond and sends them via the road through Seven Pines, which is about two hours' travel, along with sending the three brigades of reserves at Savage Station along a different road- this means that reinforcements arrive starting when Longstreet is nearly two miles north of the bridge, but they arrive pretty much all at once and form a continuous line.

At this point, both commanders can do some basic calculations.

McClellan knows that this can't be the same force that attacked him yesterday, their route to get here would have been over 25 miles long and there's still fighting going on to the north (heavy skirmishing). So he has reason to believe Richmond may have been weakened, but his own estimation of enemy force suggests that it's not cripplingly.
Lee has just seen a major arrival of reinforcements in the south (coming all at once), and he's had accounts from Jackson and the Hills that both saw Union reinforcements arrive the previous day. So he has reason to believe that McClellan's centre has been weakened, and sends orders as such - press the attack in the centre while keeping up the pressure on the flanks.

The attack in the centre doesn't go very well - McClellan still has ten brigades packed into the three miles between the Foot Bridge and Oak Grove, and they're in works - and the Confederate casualties here are quite serious. Then McClellan makes movements toward crossing the White Oak on the White's Tavern Road, and Longstreet falls back to avoid being cut off.

Overall result: it's a bloody two-day battle, and McClellan has overall got the better of it. Lee's attack started as an echelon and evolved into a move pressuring both flanks before attacking in the centre, with shades of Gettysburg in the most broad way, but with fewer casualties than that battle.

Estimate (bit of a WAG)

Jackson actions on the northern flank. 2,500 Confederate casualties and 2,000 Union casualties on the first day, 500 each on the second.
Stuart's raid and cavalry actions: 350 Confederate casualties, 600 Union.
Hills: 4,000 Confederate casualties, 2,000 Union. Second day 1,000 Confederate casualties and 300 Union.
Demonstrations in the centre: about 600 Confederate casualties, 500 Union (mostly skirmishing)
Longstreet: 2,500 Confederate casualties, 3,000 Union (largely due to the major attack on the bridge brigade early on)
Final attack in the centre: 5,000 Confederate casualties, 2,500 Union

Sum total 16,450 Confederate casualties, 11,400 Union. (Slightly worse for the CSA comparatively than the Seven Days battles, but then they are facing a much bigger army than they did then).

 

[Saphroneth]

At this point I think the next question is reinforcements. The timeline's moved past the point of the historical beginning of the Seven Days, and historically McClellan and Lee did both get reinforced after this point - specifically McClellan got two brigades and Lee got a bit more than that, but there were also several thousand troops that historically only made it as far as Fort Monroe.

What I might assume is that Lee gets his historical reinforcements and that McClellan gets the troops which historically were sent either to him or to Fort Monroe (except those derived from the brigades which in this hypothetical he already has, of course). This keeps the strength of both forces up without disrupting the events elsewhere.


Meanwhile, McClellan's ops resume their advance timetable. He'll probably make a few minor changes (the brigades along Tolopatamoy creek will be more forwards deployed to avoid a gap for raiding troops to get through, pulling back from Mechanicsville slightly to allow him to retain a reserve north of the Chickahominy) and pull back the brigades involved in repelling Longstreet somewhat, but since his troops facing Richmond are relatively fresh they should be able to make a limited advance the day after the conclusion of the battle (which was June 26; this would be June 27). This should pretty much take the Fair Oaks area, and once the guns are moved up place the main Confederate resistance line under artillery bombardment.

 

[rbasin]

McClellan could be reinforced by Halleck's entire army from the west. Still doesn't mean he'd do anything.

 

[Saphroneth]

McClellan could be reinforced by Halleck's entire army from the west. Still doesn't mean he'd do anything.

What do you base that assertion on? McClellan was clearly willing to attack Richmond in June 1862, because that's what he was doing - the actions at Oak Grove, Garnetts Hill and Goldings Farm testify to it. Indeed, he began attacking as soon as the ground was dry enough to make attacks feasible, and did so even at the cost of weakening his flank.

Indeed, McClellan's actions here during his first attacks aren't anything different to what he had planned or indeed did (though I've since found that the timing should be shifted to the 25-27 June period for those) except that since 1st Corps has arrived he can post them north of the river to cover his flank. It's the difference between having the surplus force to attack safely and having to weaken one's flank to allow an attack - and historically McClellan was willing to weaken his flank to get the attack in, it's just that Lee pounced on it.