McClellan McClellan on the offensive

[Belfoured]

I have no doubt that McClellan was made aware of the straggling situation though I don't know that he would have known to what extent. I think I even remember reading about him getting reports of Rebel stragglers. Having said that, I have my doubts that it was as widespread as some historians would have us believe (I never conceded to "high level of straggling."

I should have been clear about "conceded" - I didn't mean you. I meant other sources that have substantiated the complaints of Lee, et al about the level. Hardly implausible, of course, given that they had just come off the 2BR Campaign, lots of green corn, etc etc.

 

[Saphroneth]

Interestingly DH Hill's report claims less than 30,000 men fought on his side at Antietam, but he also claims that had all the stragglers been up the battle would have been a Confederate win in only a couple of hours with McClellan's obliteration.

With the historical strength reports for Lee's force as early as 30 September, and reported Confederate casualties, then DH Hill's claim of 30,000 men would imply well over a 50% straggle...

 

[Scott1967]

You say you respect both his knowledge and historic research and yet you won't give him any credibility. Seriously, you have to take off those blinders of yours Scott. You have been so brainwashed that you can't or won't stop to consider anything other than what you have been spoon fed by the historians. To study the history of the American Civil War and particularly when dealing with controversial figures such as George McClellan, requires a lot of objectivity and the posing of questions and well as looking for the answers. "History is a fable agreed upon, wrote Napoleon. It's up to the serious student to seek out the truth.

Not at all I have the greatest respect for https://civilwartalk.com/members/saphroneth.19683/ https://civilwartalk.com/members/67th-tigers.636/ Their knowledge is second to none but I also know they are both McClellan advocates and sometimes charts and numbers do not tell the full story and can sometimes blind you to the simple and obvious.

I tend use common sense with figures and like many people come to conclusions but I fully admit people have different views Moe and to be fair I was not a fan of McClellan and still am not however Sep and Tigers did ease my disdain for McClellan in another thread.

Historians can also warp history and are not to be fully trusted But I digress.

So my simplistic view is this.

Fact 1 = McClellan overestimated the CSA army strength in the Peninsular campaign by a large margin.
Fact 2 = Same as above but for the Sharpsburg campaign.
Fact 3 = He was replaced on both occasions.
Fact 4 = He was never considered for serious command again.
Fact 5 = Burnside and Hooker were not concerned to the extent that McClellan was when estimating CSA numbers because in the short space of time since McClellan had been replaced Army intelligence had been improved to such an extent that they were confident they had the numbers to get the job done unlike McClellan.
Fact 6 = McClellan lost the 1864 elections because of his stance on the war he repeatably gave speeches asking for a peace conference with the Confederacy and an end to the war.

 

[DanSBHawk]

You say you respect both his knowledge and historic research and yet you won't give him any credibility. Seriously, you have to take off those blinders of yours Scott. You have been so brainwashed that you can't or won't stop to consider anything other than what you have been spoon fed by the historians. To study the history of the American Civil War and particularly when dealing with controversial figures such as George McClellan, requires a lot of objectivity and the posing of questions and well as looking for the answers. "History is a fable agreed upon, wrote Napoleon. It's up to the serious student to seek out the truth.

Perhaps you should spend a little time here and get a feel for the members and the discussions before adopting a condescending attitude?

 

[Moe Daoust]

Not at all I have the greatest respect for https://civilwartalk.com/members/saphroneth.19683/ https://civilwartalk.com/members/67th-tigers.636/ Their knowledge is second to none but I also know they are both McClellan advocates and sometimes charts and numbers do not tell the full story and can sometimes blind you to the simple and obvious.

I tend use common sense with figures and like many people come to conclusions but I fully admit people have different views Moe and to be fair I was not a fan of McClellan and still am not however Sep and Tigers did ease my disdain for McClellan in another thread.

Historians can also warp history and are not to be fully trusted But I digress.

So my simplistic view is this.

Fact 1 = McClellan overestimated the CSA army strength in the Peninsular campaign by a large margin.
Fact 2 = Same as above but for the Sharpsburg campaign.
Fact 3 = He was replaced on both occasions.
Fact 4 = He was never considered for serious command again.
Fact 5 = Burnside and Hooker were not concerned to the extent that McClellan was when estimating CSA numbers because in the short space of time since McClellan had been replaced Army intelligence had been improved to such an extent that they were confident they had the numbers to get the job done unlike McClellan.
Fact 6 = McClellan lost the 1864 elections because of his stance on the war he repeatably gave speeches asking for a peace conference with the Confederacy and an end to the war.

That's all very interesting Scott. Thanks for sharing.

 

[Moe Daoust]

Perhaps you should spend a little time here and get a feel for the members and the discussions before adopting a condescending attitude?

My apologies if you mistook my advise to Scott as being condescending Dan. It was not meant to be. Now that you are here, any thoughts on my original post "Would anyone like to take a shot at explaining why McClellan, outnumbered as he supposedly believed he was, would have taken the offensive at Antietam?"

 

[DanSBHawk]

My apologies if you mistook my advise to Scott as being condescending Dan. It was not meant to be. Now that you are here, any thoughts on my original post "Would anyone like to take a shot at explaining why McClellan, outnumbered as he supposedly believed he was, would have taken the offensive at Antietam?"

I think your idea about McClellan purposefully inflating numbers is probably right.

But Scott is right as well that sometimes the advocates for these Civil War figures can skew the truth at times.

 

[Saphroneth]

Fact 5 = Burnside and Hooker were not concerned to the extent that McClellan was when estimating CSA numbers because in the short space of time since McClellan had been replaced Army intelligence had been improved to such an extent that they were confident they had the numbers to get the job done unlike McClellan.

I can't help but think that you also need to consider two things here.

The first is that when they were confident they had the numbers to get the job done they were apparently not correct - unless, that is, they failed for reasons other than the balance of strength.

The second is that one of the factors in making them both confident is that they had a much larger strength advantage over their CSA opponents than McClellan did.

Burnside was confident he had the numbers to get the job done with 176,400 Aggregate Present (three grand divisions plus 11th and 12th Corps, December 10) when Lee had 91,670 Aggregate Present (whole army, December 10); even if he was overestimating Lee by 30% he'd still think he had a 3:2 advantage.

Hooker was confident he had the numbers to get the job done when he had 158,000 Aggregate Present (April 30 Army of the Potomac number) when Lee had 77,400 Aggregate Present (March return, incl. Valley District). Even if he was overstimating Lee by 30% he'd still think he had a 3:2 advantage.


In both cases the true value for the Union commander's strength is double the true value for the Confederate commander's strength. This is something that has to be factored in - indeed, look at what happens in the Loudoun Valley campaign (when the true value for McClellan's strength is double the true value for Lee's strength and his offensive movement has been approved) and he heads off south at speed.


In fact the difference between McClellan's strength estimates and Hooker's strength estimates is in how uncertainties in the estimated enemy orders of battle were resolved. For Hooker uncertainties were dropped, for McClellan they were included. (The actual gathering of the intel was much the same for both people.) I've not seen a Burnside strength estimate before.

Fact 6 = McClellan lost the 1864 elections because of his stance on the war he repeatably gave speeches asking for a peace conference with the Confederacy and an end to the war.

He did? That surprises me; would you be able to provide the speech/es? My understanding is that the 1864 Democratic campaign was badly disjointed because McClellan had repudiated the Peace plank of the platform but the campaign still included it.

 

[Moe Daoust]

I think your idea about McClellan purposefully inflating numbers is probably right.

But Scott is right as well that sometimes the advocates for these Civil War figures can skew the truth at times.

Very true Dan, Conrad and Eckenrode being a prime example of skewing the truth regarding McClellan. Having said that, I can assure you that the same applies to many of the anti McClellan types. I'm sure you've heard the adage regarding the three phases of truth, "First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as self-evident. That is the biggest problem in attempting to present "the truth" regarding McClellan.

Do you want to take a stab at answering the question I posed in when I started this thread, "Would anyone like to take a shot at explaining why McClellan, outnumbered as he supposedly believed he was, would have taken the offensive at Antietam?"

 

[Scott1967]

He did? That surprises me; would you be able to provide the speech/es? My understanding is that the 1864 Democratic campaign was badly disjointed because McClellan had repudiated the Peace plank of the platform but the campaign still included it.

Yes your right, He did give speeches that endorsed peace but under the conditions of preserving the Union however he did endorse a return to the status quo of before 1861 in his acceptance speech for the democratic nomination thus many saw him as pandering towards the Souths needs and advocating their justification for war.

He wasn't helped by the peace democrats who wanted a negotiated peace with the Confederacy and thus as you state split the party.

 

[Saphroneth]

Yes your right, He did give speeches that endorsed peace but under the conditions of preserving the Union however he did endorse a return to the status quo of before 1861 in his acceptance speech for the democratic nomination thus many saw him as pandering towards the Souths needs and advocating their justification for war.

The odd thing is that that (reunification under the status quo) is what Lincoln was offering even in the Hampton Roads confedernce in 1865!

I tend to the view that McClellan and Lincoln were actually quite close together in their views on slavery (i.e. slavery bad but the destruction of the Union worse), but they had different views on the best way to reduce the number of slaves. Lincoln the politician felt that a military measure (the emancipation proclamation, explicitly a wartime measure conducted by the movement of the Federal armies) was best, while McClellan the military man argued in his Harrisons Landing letter for a civilian legal solution (the forced purchase and then emancipation of the entire slave population of a state at once).

 

[Saphroneth]

As to the question about why McClellan took the offensive at Antietam, I think there are these possibilities. They may not be mutually exclusive.

1)
McClellan did not know how much of Lee's army had reached Antietam by the 17th (or how much would reach Antietam by dawn on the 17th when he was making his plans on the 16th), and attacked because he thought he would have superiority over the amount of Lee's army that had reached Sharpsburg by that time. (Notably at the time his attacks launched off five of his own divisions hadn't arrived yet - all of Franklin's wing, plus Morell and Humphreys.)

2)
McClellan's estimate of the coherence of Lee's army (after the defeat at South Mountain) was such that he felt his army had a morale ascendancy and could fight better than Lee's army man for man. This would perhaps have been reinforced by the stragglers swept up on the road.

3)
McClellan's attack was intended to be an offensive with limited and managed risk, where he didn't commit his whole force and as such was not vulnerable to the destruction of his army. In this model he hoped for a decisive result (with the movement by 9th Corps) but would be satisfied if he just did damage to Lee and ended his invasion - McClellan is the one whose national army is swelling rapidly in size.

4)
McClellan's estimate of enemy strength actually in the Maryland Campaign allowed for the possibility that the enemy was as strong as he said, but he took actions that would allow him to damage the enemy if it turned out his estimate was high. (i.e. if GW Smith's division was not present.)

5)
McClellan was attacking because he'd been ordered to.


With hindsight I think McClellan was probably misled by (1), and that he would have been better off waiting a day and attacking on the 18th.

 

[Moe Daoust]

As to the question about why McClellan took the offensive at Antietam, I think there are these possibilities. They may not be mutually exclusive.

1)
McClellan did not know how much of Lee's army had reached Antietam by the 17th (or how much would reach Antietam by dawn on the 17th when he was making his plans on the 16th), and attacked because he thought he would have superiority over the amount of Lee's army that had reached Sharpsburg by that time. (Notably at the time his attacks launched off five of his own divisions hadn't arrived yet - all of Franklin's wing, plus Morell and Humphreys.)

2)
McClellan's estimate of the coherence of Lee's army (after the defeat at South Mountain) was such that he felt his army had a morale ascendancy and could fight better than Lee's army man for man. This would perhaps have been reinforced by the stragglers swept up on the road.

3)
McClellan's attack was intended to be an offensive with limited and managed risk, where he didn't commit his whole force and as such was not vulnerable to the destruction of his army. In this model he hoped for a decisive result (with the movement by 9th Corps) but would be satisfied if he just did damage to Lee and ended his invasion - McClellan is the one whose national army is swelling rapidly in size.

4)
McClellan's estimate of enemy strength actually in the Maryland Campaign allowed for the possibility that the enemy was as strong as he said, but he took actions that would allow him to damage the enemy if it turned out his estimate was high. (i.e. if GW Smith's division was not present.)

5)
McClellan was attacking because he'd been ordered to.


With hindsight I think McClellan was probably misled by (1), and that he would have been better off waiting a day and attacking on the 18th.

Very insightful and well thought out post! I agree, in concept, with all of your points except 5) and would like to know where you get this impression from. Do you have a citation in which McClellan is ordered to attack Lee on Sep. 17. I believe Lincoln did write him, urging him to destroy Lee's army but I never got the impression it was an order to "attack." Again, excellent post. Thank you!

 

[Saphroneth]

Very insightful and well thought out post! I agree, in concept, with all of your points except 5) and would like to know where you get this impression from. Do you have a citation in which McClellan is ordered to attack Lee on Sep. 17. I believe Lincoln did write him, urging him to destroy Lee's army but I never got the impression it was an order to "attack." Again, excellent post. Thank you!

I included it for completeness, because of the letter you cite - "destroy the rebel army if at all possible". If McClellan felt it was "at all possible" and that the letter was an order then I suspect he would have felt bound to obey it.

This is based on incidents on the Peninsula (particularly the position of the supply route from White House Landing) which indicated that McClellan would obey orders even if he didn't necessarily think they were a good idea. It's just a supposition though.

 

[Saphroneth]

It seems to me that you can sort of see McClellan's objectives as being:

- Avoid another Second Bull Run
- Avoid letting Lee go after Washington
- Drive Lee out of the North
- Relieve Harpers Ferry
- Do heavy damage to Lee's army
- Kill Lee's army


And the operational scheme is based on this.

In the early phase of the campaign McClellan is moving out of Washington in corps line abreast, leapfrogging forwards in case he comes into contact with the enemy. Stuart's screen is still around and east of Frederick until late September 12th, and indeed Lee himself doesn't march out of Frederick until September 10 (main body) and 11 (DH Hill). This is an advance to contact because Lee might be waiting to draw McClellan into a major battle, and at this point McClellan's force with his army is a bit more than 80,000 PFD (about 85,000 once Weber's brigade has joined, remembering that several regiments haven't yet and nor have Morell and Humphreys) - which is within the brackets of his estimate of Lee's strength. As such at this point McClellan thinks it important to have his whole force able to fight on contact.

Once Frederick is liberated and SO191 found (afternoon of the 13th), the conditions change. McClellan now knows the Confederates are marching divided, and so he pushes his force through to South Mountain where the attack begins on the Rebel rearguard.
There is the scope on the 14th for McClellan to fulfil several objectives at once:

End Lee's invasion of the North - if most of Lee's army is south of the Potomac and McClellan can cut it off from joining the portion north of the Potomac, the continued operation of a small Confederate force in Maryland and Pennsylvania is untenable. This means breaking through at least one South Mountain gap.
Relieve Harpers' Ferry and do heavy damage to Lee's army - if Franklin's wing can break through at Crampton's Gap, there is the prospect of trapping McLaws' wing in the Pleasant Valley (especially if the Harpers Ferry garrison is holding the Maryland Heights) which means about ten of Lee's brigades could be captured. (McClellan probably doesn't know the exact number here but it's two divisions.) This would also allow for the relief of Harpers Ferry.

There is however no scope to kill the Army of Northern Virginia because a significant chunk of it (Jackson's wing, Walker's division) are south of the Potomac (and thus immune to attack). McClellan would have known from SO191 that there was one "command" and one "division" (Longstreet and DH Hill) north of the Potomac and one of each (Jackson and Walker) south of it; Longstreet's "command" is at Boonsborough (actually Hagerstown) and could evacuate via Williamsport or the Shepherdstown fords if that was felt vital.


As things actually developed, the South Mountain Gaps were broken through but Harpers Ferry surrendered and McLaws' wing was able to get out of the trap.
The 15th sees a pursuit where Longstreet's wing pulls back behind Antietam creek, and then Lee goes firm (and stays there over the 16th).

Looking again at the list of objectives, McClellan can now throw 1st Corps across the road north of Sharpsburg (the Hagerstown road) and that's all he really needs to do to end this part of Lee's invasion of the north. Lee however might have one of several plans:
- he might be planning on concentrating his whole army at Sharpsburg and moving north by cutting through McClellan's right wing.
- he might be planning on moving south of the Potomac and then re-entering Maryland, either via Harpers Ferry or via Williamsport.
- he might be planning on having Jackson make a run at Washington, either with this part of his army still at Sharpsburg or not.


If this part of Lee's army retreats over the river, McClellan only needs a small part of his army to stop them re-entering here and he can then aim to hold the line of the Potomac. But if this part of Lee's army doesn't do that, it could be acting as a fixing force (while the rest acts as a turning force) and tie up too much of McClellan's army to respond to a Williamsport movement. (Couch is blocking a Harpers Ferry movement - originally it was all of Franklin but McClellan pulled in Slocum and Smith.)

This I think leads to the logic that IF a major part of Lee's army is not at Sharpsburg THEN McClellan might actually feel required to attack it (to thus defeat it, and free up troops to respond to whatever Lee's next operational movement is). Meanwhile if most of Lee's army is at Sharpsburg then an offensive not conducted a l'outrance has the prospect of doing damage (and possibly more if the 9th Corps movement comes off) while since most of Lee's army is there there's not as much risk of a wide ranging movement.



This is the insight I wanted to mention. If you assume that McClellan did think that Lee's army was about 100,000 (pre-straggle), then:

- If ~30,000 (30%) of Lee's men are at Sharpsburg and 70,000 elsewhere, crush them quickly so you can respond to what the 70,000 are doing. It's a serious blow but not a crippling one to Lee's army (it's still ~70% intact), but the important thing here is to free up the troops.
- If ~50,000 of Lee's men are at Sharpsburg and 50,000 elsewhere, you have the prospect to inflict massive damage on Lee's army and you can free up troops to respond to what Lee is doing with the other half.
- If ~70,000 of Lee's men are at Sharpsburg and 30,000 elsewhere, there isn't really as much of a worry about what that other formation is doing. You can attack without nearly so many worries - so long as you don't open the path for this formation to get out into the rest of the North, Lee has to withdraw back over the Potomac. It's a chance to do some damage and possibly conduct a concentric attack.
- If all of Lee's men are at Sharpsburg, same basic deal. Chance to do some damage.

I think this might be part of why it is that Lee moved on the 17th.

 

[Moe Daoust]

I included it for completeness, because of the letter you cite - "destroy the rebel army if at all possible". If McClellan felt it was "at all possible" and that the letter was an order then I suspect he would have felt bound to obey it.

This is based on incidents on the Peninsula (particularly the position of the supply route from White House Landing) which indicated that McClellan would obey orders even if he didn't necessarily think they were a good idea. It's just a supposition though.

As you know, most historians have criticized McClellan for his habit of overstating the enemy's numbers. One historian, a McClellan detractor who shall remain nameless, recently wrote me "he [McClellan] firmly believed he was, from first to last, outnumbered by the enemy." He goes on to suggest that McClellan's moves and tactics were those of "a general outnumbered." I disagree entirely with this view and have set my case out in my "One Plus One Equals 200,000" article, which I've posted on this site.

Of course, most students of the Civil War subscribe to that historian's views, which is why I posed my question at the beginning of this thread, "Would anyone like to take a shot at explaining why McClellan, outnumbered as he supposedly believed he was, would have taken the offensive at Antietam?" Frankly, I hoped that the question would stump a few and cause them to rethink the view that McClellan honestly believed he was outnumbered. Much to my surprise, most, if not all, of those who responded did an about face on the popular theory, as put forth by my historian acquaintance, and now suggested that McClellan did not believe in that 120,000 figure and that this, essentially, is why he went on the offensive at Antietam. One of the posters suggested McClellan probably figured Lee had 65,000 men and another put Lee's numbers on par with McClellan's which happens to be my humble guess. Go figure!

Never, in my wildest dreams, however, did I expect to get such an amazingly insightful response as yours and have copied it into my research files. Of course, much of what you proposed is speculative being that we have no way of knowing what what going on in McClellan's mind in those days but I don't think you were far off the mark.

So, all in all, I guess I can consider my experiment as being a success insofar as it now appears that some members of this group share in my belief that McClellan purposely overstated Lee's numbers and that his moves and tactics at Antietam were not those of a general outnumbered.

 

[Rebforever]

The question I have always had is why did McClellan let General Lee escape?

 

[Saphroneth]

The question I have always had is why did McClellan let General Lee escape?

Simple - he had no reliable way of preventing it.


If I may venture to provide a map (it's simplifying the tactical geography considerably but for these purposes the operational geography is what counts, and this shows the fords and river crossings at least)

Lee is in red, obviously.
The basic issue is that Lee has a line of retreat (to Boteler's Ford) and to prevent Lee escaping south McClellan has to get troops between Lee and Boteler's Ford. This was the purpose of the movement by 9th Corps over the Lower (Rohrbach/Burnside) bridge; it was attempted but it failed, partly because AP Hill turned up and partly because of the strength of the move (i.e. one corps), though Burnside blunders may also have played a role.

McClellan doesn't really have the troops to strengthen that move by much. Of his other corps:

1st Corps, 2nd Corps and 12th Corps are all part of the attack in the north and are why Lee had to strip his flank to begin with. If you weaken the movement over the Upper Bridge for the morning attack then the attack might not be able to get over the bridge in the first place (i.e. if Lee can leave a few more brigades garrisoning the area).
6th Corps is needed in the north to prevent the right wing giving way and letting Lee escape to the north (which would be worse than Lee getting away to the south, since at least if Lee gets away to the south the invasion of the North is effectively over.)
Half of 5th Corps is skirmishing around the Middle Bridge (Porter is at Porterstown - coincidence? I can't tell when Porterstown was named) and the other half is the only reserve.

And that's it for troops available.


So what that means is that McClellan didn't "let" Lee get away, not as such. He tried to stop Lee getting away with a one-corps hook around Lee's flank, and it failed; what this suggests is that McClellan thought it was "worth trying" but that it was not a guaranteed success.



The only alternative that this map offers is for 9th Corps to hook clear around to the bridge right near the mouth of the Antietam, though in that case the hooking movement would be even weaker (as you'd need to guard the Rohrbach/Burnside Bridge to prevent the Confederates using it to split 9th Corps off from the rest of the army). It is an alternative though.

(In the past I thought there was the option to have Franklin instead come along the south side of the Potomac and block Boteler's Ford that way, but since then I've determined that Thomas' Brigade would probably stymie that.)

 

[jackt62]

So, all in all, I guess I can consider my experiment as being a success insofar as it now appears that some members of this group share in my belief that McClellan purposely overstated Lee's numbers and that his moves and tactics at Antietam were not those of a general outnumbered

I am by no means an expert on McClellan but understand the common perception that he typically used inflated numbers to exaggerate the real strength of the ANV. There is of course, a counter prevailing view to that perception, which is often expressed by members of this forum. So without taking "sides" on this matter, is there a possibility that McClellan might have put forth inflated numbers for political reasons, while privately basing his actions on the true strength of the enemy? McClellan might have been a more cautious and deliberative commander than Lee, but Little Mac was by no means the incompetent general he is sometimes made out to be. As far as Antietam is concerned, McClellan's discovery of the Lost Order might be a more important consideration than Lee's raw numbers, given that Lee's dispersion of his Corps gave Mac an opportunity to confront the ANV and attack it in detail. On top of which the incursion into Maryland itself demanded a strong response: Lincoln having recently relied again on McClellan after the John Pope fiasco, must have placed Mac under great pressure to mount effective measures to counter the incursion.

 

[Moe Daoust]

It seems to me that you can sort of see McClellan's objectives as being:

- Avoid another Second Bull Run
- Avoid letting Lee go after Washington
- Drive Lee out of the North
- Relieve Harpers Ferry
- Do heavy damage to Lee's army
- Kill Lee's army


And the operational scheme is based on this.

In the early phase of the campaign McClellan is moving out of Washington in corps line abreast, leapfrogging forwards in case he comes into contact with the enemy. Stuart's screen is still around and east of Frederick until late September 12th, and indeed Lee himself doesn't march out of Frederick until September 10 (main body) and 11 (DH Hill). This is an advance to contact because Lee might be waiting to draw McClellan into a major battle, and at this point McClellan's force with his army is a bit more than 80,000 PFD (about 85,000 once Weber's brigade has joined, remembering that several regiments haven't yet and nor have Morell and Humphreys) - which is within the brackets of his estimate of Lee's strength. As such at this point McClellan thinks it important to have his whole force able to fight on contact.

Once Frederick is liberated and SO191 found (afternoon of the 13th), the conditions change. McClellan now knows the Confederates are marching divided, and so he pushes his force through to South Mountain where the attack begins on the Rebel rearguard.
There is the scope on the 14th for McClellan to fulfil several objectives at once:

End Lee's invasion of the North - if most of Lee's army is south of the Potomac and McClellan can cut it off from joining the portion north of the Potomac, the continued operation of a small Confederate force in Maryland and Pennsylvania is untenable. This means breaking through at least one South Mountain gap.
Relieve Harpers' Ferry and do heavy damage to Lee's army - if Franklin's wing can break through at Crampton's Gap, there is the prospect of trapping McLaws' wing in the Pleasant Valley (especially if the Harpers Ferry garrison is holding the Maryland Heights) which means about ten of Lee's brigades could be captured. (McClellan probably doesn't know the exact number here but it's two divisions.) This would also allow for the relief of Harpers Ferry.

There is however no scope to kill the Army of Northern Virginia because a significant chunk of it (Jackson's wing, Walker's division) are south of the Potomac (and thus immune to attack). McClellan would have known from SO191 that there was one "command" and one "division" (Longstreet and DH Hill) north of the Potomac and one of each (Jackson and Walker) south of it; Longstreet's "command" is at Boonsborough (actually Hagerstown) and could evacuate via Williamsport or the Shepherdstown fords if that was felt vital.


As things actually developed, the South Mountain Gaps were broken through but Harpers Ferry surrendered and McLaws' wing was able to get out of the trap.
The 15th sees a pursuit where Longstreet's wing pulls back behind Antietam creek, and then Lee goes firm (and stays there over the 16th).

Looking again at the list of objectives, McClellan can now throw 1st Corps across the road north of Sharpsburg (the Hagerstown road) and that's all he really needs to do to end this part of Lee's invasion of the north. Lee however might have one of several plans:
- he might be planning on concentrating his whole army at Sharpsburg and moving north by cutting through McClellan's right wing.
- he might be planning on moving south of the Potomac and then re-entering Maryland, either via Harpers Ferry or via Williamsport.
- he might be planning on having Jackson make a run at Washington, either with this part of his army still at Sharpsburg or not.


If this part of Lee's army retreats over the river, McClellan only needs a small part of his army to stop them re-entering here and he can then aim to hold the line of the Potomac. But if this part of Lee's army doesn't do that, it could be acting as a fixing force (while the rest acts as a turning force) and tie up too much of McClellan's army to respond to a Williamsport movement. (Couch is blocking a Harpers Ferry movement - originally it was all of Franklin but McClellan pulled in Slocum and Smith.)

This I think leads to the logic that IF a major part of Lee's army is not at Sharpsburg THEN McClellan might actually feel required to attack it (to thus defeat it, and free up troops to respond to whatever Lee's next operational movement is). Meanwhile if most of Lee's army is at Sharpsburg then an offensive not conducted a l'outrance has the prospect of doing damage (and possibly more if the 9th Corps movement comes off) while since most of Lee's army is there there's not as much risk of a wide ranging movement.



This is the insight I wanted to mention. If you assume that McClellan did think that Lee's army was about 100,000 (pre-straggle), then:

- If ~30,000 (30%) of Lee's men are at Sharpsburg and 70,000 elsewhere, crush them quickly so you can respond to what the 70,000 are doing. It's a serious blow but not a crippling one to Lee's army (it's still ~70% intact), but the important thing here is to free up the troops.
- If ~50,000 of Lee's men are at Sharpsburg and 50,000 elsewhere, you have the prospect to inflict massive damage on Lee's army and you can free up troops to respond to what Lee is doing with the other half.
- If ~70,000 of Lee's men are at Sharpsburg and 30,000 elsewhere, there isn't really as much of a worry about what that other formation is doing. You can attack without nearly so many worries - so long as you don't open the path for this formation to get out into the rest of the North, Lee has to withdraw back over the Potomac. It's a chance to do some damage and possibly conduct a concentric attack.
- If all of Lee's men are at Sharpsburg, same basic deal. Chance to do some damage.

I think this might be part of why it is that Lee moved on the 17th.

The question I have always had is why did McClellan let General Lee escape?
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I am by no means an expert on McClellan but understand the common perception that he typically used inflated numbers to exaggerate the real strength of the ANV. There is of course, a counter prevailing view to that perception, which is often expressed by members of this forum. So without taking "sides" on this matter, is there a possibility that McClellan might have put forth inflated numbers for political reasons, while privately basing his actions on the true strength of the enemy? McClellan might have been a more cautious and deliberative commander than Lee, but Little Mac was by no means the incompetent general he is sometimes made out to be. As far as Antietam is concerned, McClellan's discovery of the Lost Order might be a more important consideration than Lee's raw numbers, given that Lee's dispersion of his Corps gave Mac an opportunity to confront the ANV and attack it in detail. On top of which the incursion into Maryland itself demanded a strong response: Lincoln having recently relied again on McClellan after the John Pope fiasco, must have placed Mac under great pressure to mount effective measures to counter the incursion.

Have you read my article "One Plus One Equals 200,000, which I've posted on this site? I think you'll find it worthwhile.