McClellan's Value on the Hagerstown Pike

rupert822

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I've been thinking recently about Antietam a good bit, and I think I may have come up with an idea I've not heard before. Apologies if I am wrong and this has been discussed.

Having come to agree with the opinion that McClellan in effect decided the outcome of the battle, i.e. Lee recrossing the Potomac at Shepherdsburg, by controlling the Hagerstown Pike the night before, early in the day of the battle and throughout the same. Agree with that or not, I don't think it is earth shattering.

But that got me thinking, why would McClellan have wanted to control the Hagerstown Pike so badly he made it the initial, and focal, point of his attack? Attacking there wasn't cutting Lee off from the river at his back, it was driving towards his exit. It dawned on me that if I want the answer to that question, I need to think like McClellan. So I went to his dispatch to Lincoln during the battle. Something along the lines of we are gaining ground, all is going well given the enemy's superior numbers. Obviously Lee's supposed numerical advantage was a long and closely held belief of McClellans', even if demonstrably false. That being said, it sure seems to me that McClellan only moved to control the Hagerstown Pike because he feared Lee's superior numbers and a possible further move north (which ironically in spite of his inferior numbers is exactly what Lee planned to do). I.e. without McClellan's delusions, maybe the main blow would not have fallen in a way that only allowed Lee one way out, back across the Potomac. If Lee had not moved across the Potomac after Antietam would emancipation have waited until Stones River? Gettysburg? It might be odd, but perhaps but for McClellans' delusions about Lee's numbers we'd live in a different country.
 
I believe that given the condition of the reconstituted Army of the Potomac, McClellan goal was to simply get Lee out of Md. By cutting off the Hagerstown Pike, he essentially gives Lee no option. I also think that McClellan recognizing the position that Lee is in, would assume Lee would fall back. The attack on the morning of the 17th would be the gentle nod to get him going.
 
My understanding is that McClellan's intent was as follows.


On the 16th, he is aware that the enemy may (in the worst case) be stronger than him in terms of total forces in the campaign - remember that on the 16th not all of either army has actually arrived, so McClellan has no way to be sure how much of Lee's force is present or how big it is.
He is however fairly sure that not all of Lee's forces have concentrated at Sharpsburg yet, but can also know that there is no way he can currently prevent Lee from uniting his army (that is, he cannot interpose himself on the route Lee will be able to use to unite his army).

On the 16th, McClellan also has no way to prevent Lee from actually retreating south of the Potomac.

Lee thus has these possibilities:
- He wants to defend against whatever attack McClellan will be launching on him, or will otherwise wait until McClellan attacks.
- He wants to retreat south of the Potomac, and then possibly move elsewhere (such as to Williamsport).
- He wants to concentrate his forces and then move north into Pennsylvania (where he could sustain his army by forage as he did in 1863).

If Lee is going to be doing the first option, then McClellan's main job is setting up a good attack on Lee.
If Lee is going to be doing the second option, McClellan currently (16th) has no way to prevent it - he can't get forces in the way - but this would mean Lee's invasion of the North was over. This is actually a pretty good outcome all things considered - Lee's invasion was very threatening and it has been neutralized.
If Lee is going to be doing the third option, then McClellan will need to stop him.

So obviously blocking the Hagerstown road is beneficial for preventing Lee from moving north.

In addition, however, there's that point about McClellan setting up a good attack on Lee.

There are fundamentally three routes by which McClellan can attack Lee. He can do so across the lower (Burnside) bridge, or he can do so across the middle bridge, or he can do so from the north (given the positions Lee has taken, only the attack from the north does not involve doing so as part of a bridge crossing).

Of those three routes:

The northern route offers the greatest potential for deploying troops. There is a defile but it is some way back from Lee's lines, and McClellan can effectively feed as many men over the upper bridge as he has available and deploy them into a powerful attack before sending them in.
The disadvantage is that if Lee is defeated on this axis then (while defeating him on this axis is a good thing) he has been forced back towards the Potomac and will be able to escape.
The middle route involves a head on attack against a part of Lee's army which is deployed on good defensive terrain, and is canalized by a bridge. It is also a route of attack which would force Lee back towards the Potomac if successful.
This is the worst route of attack, and should only be threatened (it can't simply be abandoned). If the enemy gives back from the middle bridge then it would be a useful way to send in reserves previously held in the centre, however.
The southern route offers the greatest potential for a decisive victory. Success on this axis would allow McClellan to cut the part of Lee's army he is facing off from the Potomac, and allow him to encircle them for a kesselsalacht that would largely shatter that part of the army.
The disadvantage of this route is that it is also canalized by a bridge, and taking the bridge is essential to allow that potential for a decisive victory.


What McClellan thus decides to do, during the afternoon of the 16th, is to put Lee in a fork - that is, to give him a choice about what bad things will happen. He begins moving troops to take up position north of Lee's army for a powerful attack from the north, and he moves 9th Corps down to the lower bridge to make a corps-scale attack from the south.

This will present Lee with a choice about how he commits his reserves, and give McClellan options about how he commits his own. Essentially wherever Lee sends his resources, the other attack becomes McClellan's "primary" attack which will be the one that does the most damage.

Scenario 1: Lee defends against the northern attack sufficiently that he is able to avoid it doing him critical damage, and this exposes his southern flank so that the 9th Corps attack can cut him off from the Potomac.
This is the best case.
Scenario 2: Lee defends against the southern attack sufficiently that 9th Corps cannot cut him off from the Potomac, and this means that he doesn't have enough troops available to fend off the attack on his northern flank.
This scenario still sees Lee defeated, but he has a clear line of retreat.
Scenario 3: Lee is strong enough that he can effectively defend against the northern attack without exposing himself to being cut off by the southern attack.
This sees Lee taking heavy blows, but able to retire in good order. However, Lee is still forced to abandon his invasion of the North, unless Lee is strong enough that he can outright win the defensive battle and the Union army ends up "fought out" and vulnerable to a counterstroke (as happened at Second Bull Run).


So on the afternoon of the 16th, McClellan has committed to a highly aggressive plan. He's going to send in several corps on the attack (1st, 12th and 9th) with 2nd, 5th and 6th available to send wherever makes sense.
As the attack actually unfolded, of course, McClellan fed 2nd and then 6th Corps in on the north - 2nd to bulk out the attack, then 6th to prevent a counterstroke. 9th Corps stalled badly at the bridge, but hadn't been defeated yet, and McClellan sent for everything disposable of 5th Corps (two brigades of Morell) to bulk out one last attack by elements of 6th Corps to either keep Lee occupied (if 9th Corps still had a chance) or exploit the disruption caused by 9th Corps (if Lee was now focused on them).
He called off that last attack once news came that 9th Corps had been broken, as at that point Lee was no longer being forced to divide his attention between two viable threats.



The fundamental problem with any idea of changing the weighting of the blows McClellan was striking on the 17th is that the attack in the south is constrained by the Lower Bridge and it took hours for Burnside to get his act together and capture it. For any extra troops sent to the south there are two issues:
1) For them to get into the fight, you need to start feeding Union troops over the bridge hours earlier (which means you need it captured hours earlier). But if Burnside takes his bridge hours earlier then you don't actually need those extra troops sent south, as 9th Corps cutting off Lee before AP Hill arrived would suffice.
2) Those extra troops have to come from somewhere, and there aren't really any troops you can pull from the rest of the fighting without fundamentally altering it.
 
I believe that given the condition of the reconstituted Army of the Potomac, McClellan goal was to simply get Lee out of Md. By cutting off the Hagerstown Pike, he essentially gives Lee no option. I also think that McClellan recognizing the position that Lee is in, would assume Lee would fall back. The attack on the morning of the 17th would be the gentle nod to get him going.
I think to call it a gentle nod is to rather mischaracterize the attacks that led to the bloodiest day of combat in American history! But the key thing here is that it's part and parcel with McClellan's concept of operations - the heavy attacks in the north are part of giving Lee only bad options. Without them then you just have an attempt to take the Lower Bridge (against which Lee can commit all his reserves without fear).
 
@rupert822 , looking over your original post again I've got a question that comes to mind. What sort of alternative course for Antietam are you envisaging from McClellan not initially focusing on the Hagerstown Pike?

It's possible I've missed something, but I have difficulty seeing how the battle can go without McClellan taking control of the Pike as part of the opening moves - except "not particularly well" because there's no space to deploy a large attack in the north and it's all coming over two defensible bridges.
 
I agree with the analysis @Saphroneth has so well articulated and would add a couple of items. The first
point is that by his actions at South Mountain, McClellan had seized the initiative in the campaign from Lee. Leaving the Hagerstown Road open would have left Lee the opportunity to retake that initiative and extend the campaign, most likely into Pennsylvania. Lee would have been in position to dictate the conditions of a future battle.

Secondly, even as the battle on the 17th had shifted to the area above Burnside's Bridge, Lee was considering a breakout to the north. Both Jackson and Lee mentioned this in their Battle Reports. To quote Jackson "In the afternoon, in obedience to instructions from the commanding general, I moved to the left with a view of turning the Federal right, but I found his numerous artillery so judiciously established in their front and extending so near to the Potomac, which here makes a remarkable bend, as will be seen by reference to the map herewith annexed, as to render it inexpedient to hazard the attempt."

Artillerist Stephen D. Lee would comment on his role in reconnoitering the Federal lines with Jackson from Nicodemus Hill on the morning of the 18th and reaching the conclusion such an attempt was unlikely to succeed. I can think of no reason other than breaking free to continue the campaign that Lee would move in that direction.
 
A good point, and it's worth considering carefully what Lee's intentions and actions were. If all Lee was trying to do was to avoid destruction then he could have retreated his whole army completely south of the Potomac on the night of the 16th, though this would be at the cost of abandoning some of his baggage. (But it's better to keep the army intact and lose baggage than lose the army and keep the baggage.)

I suspect that Lee's plans at the time included the idea of moving his baggage to Williamsport and linking back up with it there.
 
If Lee really wanted to keep going north, he should've done that from the VA side of the Potomac. He was much safer there. He preferred trying to stay in MD as long as possible. His best bet to go into PA from the MD side of the river was the afternoon the 15th, with Jackson's men going to the Potomac from Harpers Ferry by staying in VA until reaching the river. But Lee also wished to make sure McLaws was safe, something not guaranteed as he was assembling the small part of his army at Sharpsburg on the 15th.

If McClellan really thought he was outnumbered, sending just one corps across the Antietam on the p.m. of the 16th made no sense. His best option to open the attack was from the north. He just didn't assemble sufficient force to do that. The 12th Corps was across the creek by very early in the morning of the 17th. Even though they were technically under Hooker's command at that time, the chance of a coordinated attack was already lost. It made a lot more sense to attack later in the day on the 17th, with two corps moving south at the same time. Perhaps that's Hooker's fault to some extent. But the army commander is the one deserving the most blame.
 
If Lee really wanted to keep going north, he should've done that from the VA side of the Potomac. He was much safer there. He preferred trying to stay in MD as long as possible. His best bet to go into PA from the MD side of the river was the afternoon the 15th, with Jackson's men going to the Potomac from Harpers Ferry by staying in VA until reaching the river. But Lee also wished to make sure McLaws was safe, something not guaranteed as he was assembling the small part of his army at Sharpsburg on the 15th.
I think the problem there is that most of Lee's trains were between Longstreet and DH Hill, and moved to Sharpsburg after South Mountain. He needs to get them out of the Sharpsburg area to safety (which means south of the Potomac) and the best chance he has to do that is to defend at Sharpsburg.


If McClellan really thought he was outnumbered, sending just one corps across the Antietam on the p.m. of the 16th made no sense. His best option to open the attack was from the north. He just didn't assemble sufficient force to do that. The 12th Corps was across the creek by very early in the morning of the 17th. Even though they were technically under Hooker's command at that time, the chance of a coordinated attack was already lost. It made a lot more sense to attack later in the day on the 17th, with two corps moving south at the same time. Perhaps that's Hooker's fault to some extent. But the army commander is the one deserving the most blame.
Well, the 12th Corps hadn't really arrived to send over the creek until pretty close to the time they were sent over. As for a coordinated attack later in the day, McClellan's intent appears to have been to hit Lee before Lee fully concentrated his army, and his plan was for a coordinated attack with 1st/12th (in the north) and 9th a short while later (in the south), with 2nd and 6th going in wherever seemed sensible.

By delaying the attack until the afternoon of the 17th, McClellan would be being more stereotypical, but less aggressive (and also losing some of the potential surprise value of a near dawn attack); those several hours of setup also offer more time for reinforcements for Lee to march along the south side of the Potomac.

I do think an attack later on the 17th is a viable option, but I don't think it's really superior (even with hindsight) to an attack in the morning with Burnside moving when he was ordered to. There's also the possibility of a fully prepared attack on the 18th, of course.

As to "if McClellan really thought he was outnumbered", don't forget that as of the 16th McClellan has no solid idea where most of Lee's army is - that is, he doesn't know how much of it has arrived - but he probably has estimates. 1st Corps moving to where they are exposes them to comparatively small danger as they have a viable line of retreat, and while I'm sure he'd prefer to send over two corps at once this gets into the time-and-motion issue - which two corps and when do they start crossing?
 
Perhaps If McC hadn't lost faith in Burnside, he would've kept the right wing in tact. That way both 1st and 9th corps could've been ready for an Antietam crossing on the 16th. But that meant Hooker would've been the subordinate to Burnside for the main attack, rather than the ranking officer on the field, as Mansfield was only a brigadier. Heck, perhaps an attack from the soon-to-be Burnside's Bridge didn't need to be made at all?
 
Perhaps If McC hadn't lost faith in Burnside, he would've kept the right wing in tact. That way both 1st and 9th corps could've been ready for an Antietam crossing on the 16th. But that meant Hooker would've been the subordinate to Burnside for the main attack, rather than the ranking officer on the field, as Mansfield was only a brigadier. Heck, perhaps an attack from the soon-to-be Burnside's Bridge didn't need to be made at all?
The reason why Burnside's wing was split up is directly related to manoeuvres on the 15th, and the fact that the 9th Corps was slow through their defile while 1st Corps was pretty quick to move through theirs.

During the pursuit on the 15th, 1st Corps (which was at the head of one of the columns) moved ahead fairly quickly, though Richardson's fresh division (which had been sent to reinforce Hooker) was pushed through ahead of them.
9th Corps meanwhile was moved to the side to be able to react if McClellan needed to send more force to Harpers Ferry, and in addition was hours late moving out of the pass (like 1st Corps they had a division pushed through ahead of them, Sykes in this case, but 1st Corps was much quicker than 9th out of the respective pass after the fresh division).

The fact that 1st and 9th Corps were at the front of the army (i.e. Burnside's wing was at the front) is what led to the fact that they got split up. McClellan needed a corps to move south into the Pleasant Valley, and 9th Corps was first in that column; McClellan needed to push his main force after Longstreet and DH Hill, and 1st Corps was part of that column.

Then when McClellan begins putting troops over the Antietam 1st Corps is the first one that's actually able to make the move (Sykes and Richardson have reached the Antietam, 1st Corps is behind Richardson).


There isn't really a way to work it out so that 1st and 9th Corps end up together, unless you have 9th Corps exit Fox's Gap and then go up north (interrupting the flow of reinforcements out of Turner's Gap, which has to stop until 9th Corps has fully joined the road - essentially once 1st Corps has passed the junction you're using you then need to delay Sumner's wing until 9th Corps has fully joined the road) and if you do that then you have no more troops available to send over the Antietam anyway- possibly less, because of the hours-long delay in 9th Corps getting moving historically.

As for making an attack from Burnside's bridge, there's two reasons for it.
One is that this is integral to McClellan's entire concept of operations for the attack. Historically he was presenting multiple threats, one of them powerful and the other decisive (the powerful threat being a multi-corps attack, the decisive one being a chance to cut Lee off from the Shepherdstown fords) and essentially trying to make it so that if Lee messes up his force distribution then McClellan defeats Lee's army. But if McClellan's attack is a single-axis attack then Lee doesn't need to make any decisions about force distribution - everything just goes north - and even in the event of a smashing success all that really can happen is that Lee is forced back towards the Potomac. His line of retreat cannot be cut.
The second is that there are going to have to be troops there anyway. As mentioned, 9th Corps was moved south (to Rohrersville historically) to potentially support 6th Corps, and McClellan has no actual way to know that this was unnecessary (remember, Harpers Ferry doesn't actually surrender until late morning of the 15th and after that Jackson could have turned on 6th Corps), so some force is going to be in that area - and, indeed, if McClellan leaves the Burnside bridge unoccupied it's a possible avenue into his rear..



My read is that McClellan's greatest source of disappointment with Burnside was precisely the Burnside Bridge issue. So I don't actually think McClellan had lost faith in Burnside yet (though even after the Burnside Bridge thing Burnside is still one of McClellan's wing commanders, and trusted on more than one occasion to form the army vanguard).
 
I don't really disagree with what you're saying on force distribution. Making the perfect alignment for an attack at Sharpsburg was quite difficult, especially with the lay of the ground and the timing of troop arrival. Perhaps more could've been done. As I ponder things more, waiting to launch a Union attack on the 18th made a lot more sense than the way the 17th played out. Sending one corps to attack from the north of town at dawn was simply not going to cut the mustard, especially without a true concentration of forces across the First Corps. One of my favorite parts of First for the Union to study and write was the section called "A Very Difficult Evening," about Hooker's command on the p.m. and early a.m. after crossing the creek, before the opening attack. Sorry for the shameless self promotion!!!

I have a theory about McC's declining faith in Burnside, although I don't think any other historian has focused on it. In August McC wrote privately to his wife saying any cause employing John Pope deserved to lose. At the same time, poor Burnside was writing his old friend Mac with hopes Pope wins a great victory in Northern VA. McC never truly trusted Burnside after that, I suggest. Also, Burnside was scolded on the 15th for not moving quickly enough west from South Mountain. McC wrote Burnside never should've been promoted above colonel, but I don't remember exactly when he first wrote that.
 
If Lee really wanted to keep going north, he should've done that from the VA side of the Potomac. He was much safer there. He preferred trying to stay in MD as long as possible. His best bet to go into PA from the MD side of the river was the afternoon the 15th, with Jackson's men going to the Potomac from Harpers Ferry by staying in VA until reaching the river. But Lee also wished to make sure McLaws was safe, something not guaranteed as he was assembling the small part of his army at Sharpsburg on the 15th.
The Harpers Ferry garrison did not signal surrender until 9:00 - 9:30 in the morning. It took hours to take possession of the town and to secure the prisoners. Jackson did not begin the march to Sharpsburg until after nightfall. Walker followed Jackson. McLaws did not cross into Harpers Ferry until the 16th and did not arrive in Sharpsburg until the morning of the 17th.

Unless Lee withdrew to Shepherdstown every step he took moved him further away from Jackson, Walker and McLaws and left the ANVa open to defeat in detail. If he went to Shepherdstown the campaign was effectively over.
 
The Harpers Ferry garrison did not signal surrender until 9:00 - 9:30 in the morning. It took hours to take possession of the town and to secure the prisoners. Jackson did not begin the march to Sharpsburg until after nightfall. Walker followed Jackson. McLaws did not cross into Harpers Ferry until the 16th and did not arrive in Sharpsburg until the morning of the 17th.

Unless Lee withdrew to Shepherdstown every step he took moved him further away from Jackson, Walker and McLaws and left the ANVa open to defeat in detail. If he went to Shepherdstown the campaign was effectively over.
And perhaps Lee should've gone to VA without another fight. I like E.P. Alexander's thought: Staying to fight at Sharpsburg was Lee's worst mistake, too big a risk for the gain.
 
I don't really disagree with what you're saying on force distribution. Making the perfect alignment for an attack at Sharpsburg was quite difficult, especially with the lay of the ground and the timing of troop arrival. Perhaps more could've been done. As I ponder things more, waiting to launch a Union attack on the 18th made a lot more sense than the way the 17th played out. Sending one corps to attack from the north of town at dawn was simply not going to cut the mustard, especially without a true concentration of forces across the First Corps. One of my favorite parts of First for the Union to study and write was the section called "A Very Difficult Evening," about Hooker's command on the p.m. and early a.m. after crossing the creek, before the opening attack. Sorry for the shameless self promotion!!!
I feel it's worth pointing out that McClellan sent one corps across on the afternoon of the 16th, and by about 9AM on the 17th had sent across three corps with a fourth (6th) to follow. There was no sense in which McClellan intended to attack with just one corps, or at least if there was then it had been changed long before the attack actually began.

An attack on the 18th is plausible, and could have been quite strong, but it would also have given the Confederates time to dig in (or, feasibly, retreat south of the Potomac) and certainly (to McClellan) would have given them time to reconcentrate their army. It would also have been "stereotypical McClellan" and we should point out here that McClellan was actually being faster and more aggressive than his stereotype would dictate.


I have a theory about McC's declining faith in Burnside, although I don't think any other historian has focused on it. In August McC wrote privately to his wife saying any cause employing John Pope deserved to lose. At the same time, poor Burnside was writing his old friend Mac with hopes Pope wins a great victory in Northern VA. McC never truly trusted Burnside after that, I suggest. Also, Burnside was scolded on the 15th for not moving quickly enough west from South Mountain. McC wrote Burnside never should've been promoted above colonel, but I don't remember exactly when he first wrote that.
My read on the situation in northern Virginia is that McClellan was hoping there would be a Union victory but that he was so unimpressed with Pope (who had after all been brought in as his direct replacement and turned out to be pretty incompetent) as to feel more than a little schadenfreude at Pope's defeat.

I think you're thinking of this section:

"I ought to rap Burnside very severely, and probably will; yet I hate to do it. He is very slow; is not fit to command more than a regiment. If I rap him as he deserves he will be my mortal enemy hereafter. If I do not praise him as he thinks he deserves, and as I know he does not, he will be at least a very lukewarm friend. I mention this merely as an instance that you will comprehend..."

Which was from 29th September, shortly before Burnside submitted his report on Antietam (where Burnside moved timings so he didn't look as bad). I suspect McClellan may have been emplying hyperbole here, but it must have been very disappointing that his friend had so completely screwed up McClellan's battle plan.

It's not exaggerating after all to say that if Burnside had attacked competently when ordered (on the 17th) then Lee would have been in a kessel and possibly either destroyed or very badly damaged.


(I basically think that all the rest of the "friction" that happened with the attack on the 17th was recoverable, but Burnside's hours of delay and blundering was irrecoverable. It let Lee focus the attention of his entire army on the northern attack.)
 
And perhaps Lee should've gone to VA without another fight. I like E.P. Alexander's thought: Staying to fight at Sharpsburg was Lee's worst mistake, too big a risk for the gain.
Eh... I'm not sure, or at least I think it's worth understanding Lee's motives. Part of the gain is essentially that Lee keeps his army's train (losing which would seriously impair the ability to campaign for months, including defensively), while another part is that I don't think Lee really understood how much McClellan had revitalized the capability of the Army of the Potomac.
Just three weeks earlier Lee (with ~140 regiments) had shattered the Army of Virginia (with ~170 regiments), and now it was at the point where the ~100 regiments of 1st, 2nd and 12th Corps, plus the ~25 of 6th Corps, could seriously threaten to outfight the significant majority of the ~160 regiments Lee already had at Sharpsburg on the morning of the 17th.
 
I have read that one thing that did surprise Lee was how quickly McClellan was able to revitalize the Army of the Potomac.
It's actually something that deserves a lot of attention in general. It's sort of viewed as inevitable, but an army that's been badly battered can be wrecked for a very long period of time.


Two examples from the Napoleonic wars.

Firstly, there's Soult in the Peninsular War (before the Battle of the Pyrenees). He took over the routed forces from Vitoria (a battle of 21 June) on 12 July (aided by a nucleus of forces that had not been routed) and launched his offensive on the 25th. This was considered very good, and the French army had three weeks recovery before Soult took it over plus another two weeks afterwards.

Secondly, there's Napoleon himself after the Battle of Waterloo. In his case he again had a nucleus of forces that had not been routed, an entire large corps (about 1/3 to 1/4 of the total French army) but considered it pointless to even try remaining with the army to rally it. The Allies entered Paris about three weeks after the battle itself.


In McClellan's case, he had a nucleus of forces that had not been routed (2nd and 6th Corps) so the situation is roughly comparable. The time from the rout (30 August) to McClellan marching out once more was a bit more than a week, and South Mountain was fought (largely by corps that had been routed) slightly more than two weeks after the rout, with the army then sustaining an extremely bloody conflict less than three weeks after Second Bull Run.

It's a good performance. It may also be why nobody else wanted to take the army out!
 
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