McClellan’s Plan at Antietam

McClellan’s Plan at Antietam

By

Michael Lang

While doing my research on the Maryland Campaign, I have found myself frequently amused and somewhat frustrated by the number of conflicting accounts and theories about the Campaign that often block my way.  While I understand that the study of history is sometimes like that by its very nature, it can be madding to determine what really happened when so many of the accounts seem to be at odds with one another. 

The numbers of men on each side of the campaign, Lee’s true objective and how well McClellan reacted to the finding of the lost order are but a few examples of how certain aspects of the Campaign that are still open to debate over 150 years later.  

In addition to these, a full and comprehensive agreement on what McClellan’s battle plan was on 17 September 1862, is one of the more problematic questions surrounding the Maryland Campaign and the Battle of Antietam. It is one I have been chasing for some time now.

When facing a crisis, it is often good to go to the source. There are literally dozens if not hundreds of primary, secondary and tertiary accounts of the battle that can be scoured for information. Surely one of these can provide the clarity desired.

Here are nine quotes\citations on what McClellan’s plan was at Antietam:

1.“The design was to make the main attack upon the enemy's left--at least to create a diversion in favor of the main attack, with the hope of something more by assailing the enemy's right--and, as soon as one or both of the flank movements were fully successful, to attack their center with any reserve I might then have on hand.” – McClellan’s After-action report of October 15 1862.

2.“My plan for the impending general engagement was to attack the enemy's left with the corps of Hooker and Mansfield, supported by Sumner's and, if necessary, by Franklin's, and, as soon as matters looked favorably there, to move the corps of Burnside against the enemy's extreme right, upon the ridge running to the south and rear of Sharpsburg, and, having carried their position, to press along the crest toward our right, and, whenever either of these flank movements should be successful, to advance our center with all the forces then disposable.”  - McClellan’s After-action report of August 4 1863 

3.“My plan for the impending general engagement was to attack the enemy's left with the corps of Hooker and Mansfield, supported by Sumner's and, if necessary, by Franklin's ; and as soon as matters looked favorably there, to move the corps of Burnside against the enemy's extreme right, upon the ridge running to the south and rear of Sharpsburg, and, having carried their position, to press along the crest towards our right; and whenever either of these flank movements should be successful, to advance our centre with all the forces then disposable.”- McClellan's own Story – Published in 1887
 
4.“The plan decided upon was to attack their left.” - Feb. 28, 1863. - McClellan’s Testimony before the Congressional Committee on the Conduct of the war.
 
5.“When McClellan made his rapid examination on the evening of the fifteenth, he concluded that an attack on the Confederate left offered better results than an attack elsewhere, and this conclusion was confirmed by a more extended examination on the morning of the sixteenth. (For reasons given elsewhere, which we consider entirely inadequate, he deferred the movement until afternoon.) The plan for the impending general engagement was to attack Lee’s left with the corps of Hooker and Mansfield, supported by Sumner’s corps (and, if necessary, by Franklin’s corps), and as soon as matters looked favorable there, to move Burnside’s corps against Lee’s right, upon the ridge running to the south and rear of Sharpsburg. Having carried these positions, he then proposed to press with the right along the crest toward Sharpsburg and, when either of these flank movements should be successful, to advance the center across the Middle Bridge with all the forces then disposable.” - Joseph Pierro. The Maryland Campaign of September 1862: Ezra A. Carman’s Definitive Study of the Union and Confederate Armies at Antietam
 
6.“The opinion I got from Burnside as to the part the Ninth Corps was to take was fairly consistent with the design first quoted, viz., that when the attack by Sumner, Hooker, and Franklin should be progressing favorably, we were "to create a diversion in favor of the main attack, with the hope of something more." It would also appear probable that Hooker's movement was at first intended to be made by his corps alone, taken up by Sumner's two corps as soon as he was ready to attack, and shared in by Franklin if he reached the field in time, thus making a simultaneous oblique attack from our right by the whole army except Porter's corps, which was in reserve, and the Ninth Corps, which was to create the "diversion" on our left and prevent the enemy from stripping his right to reinforce his left.”- Battles & Leaders of the Civil War - Volume 2 By Jacob D. Cox, Major-General, U.S.V
 
7.“As originally conceived, McClellan’s plan called for an opening attack on one enemy flank. This initial assault was to accomplish two objectives: first, to discover if Lee intended to make a determined stand and to do so in a way less bloody than a frontal assault on the heights of Sharpsburg; and second— if Lee showed determination— to press the Confederates hard enough to make them strip their lines elsewhere in response to the threat. Then, McClellan planned for a follow-up attack several hours later on the opposite flank to take advantage of the thinned enemy ranks. He was willing to accept success where he found it, however, and “whenever either of these flank movements should be successful, he proposed to throw his best troops against what he assumed would be the much-weakened enemy center. It was this final blow against the heart of Lee’s line on Cemetery Hill— and not either of the flank attacks— which he expected to crush the Confederate army. As a result, he intended to make probing attacks on each flank that would divert the Confederates’ attention and cause them to rearrange and weaken their line. Initially, McClellan did not intend to commit more than a single corps to either flank attack; nor did he propose to launch the attacks simultaneously, or expect to be able to achieve surprise in either.” - Harsh, Joseph L. Taken at the Flood: Robert E. Lee and Confederate Strategy in the Maryland Campaign of 1862
 
8.“By 2:00 pm McClellan had made up his mind on the plans of battle. He would first attack the Confederate left and right as diversions for a main attack at the center.” - The Gleam of Bayonets James Murfin
 
9.“Consequently, as McClellan described it in his preliminary report on the campaign written a month later, his “design” was to throw the main weight of his attack against the Confederate left or northern flank. Beyond that certainty, there is no clear statement of the rest of his plan for the coming battle. He issued no written general orders on September 16. He called no conference of his corps commanders to outline his intentions. The explanations in his preliminary report, in his official report written in 1863, and in his postwar memoirs are at variance one with another and heavily embroidered with hindsight. In any case, it was his intention also to force a crossing at the Rohrbach Bridge against the Confederate right—whether in conjunction with the assault against the left or only after it developed, whether as a diversion or a full-scale attack, was never made clear. When “one or both of the flank movements were fully successful,” he wrote, he intended to attack the enemy’s center “with any reserve I might then have on hand.” -Landscape Turned Red: The Battle of Antietam- Stephen W Sears

The first four quotes are from the general himself written at various points after the battle. Quote 3, from his autobiography, is merely a regurgitation of his second after-action report written in August 1863 (quote 2). Quote 4 is a partial statement from McClellan's testimony that was essentially a summary of what happened and not necessarily what he was planning. Only quote 1, written less than a month after the battle, strays from what seems be McClellan’s “Official” story thereafter. The main difference being what was to have been the main attack and what was to have been the supporting attack. McClellan seems to be indicating that his idea was to have the attack on Lee’s left be the supporting attack, but changed that story in later accounts to Burnside’s being the supporting attack. 

According to modern military doctrine, offensive tactics calling for a main attack and a supporting attack(s) against an enemy position have or should have very distinctive characteristics. The words to describe these in 1862 may be different, but the ideas behind them are the same.

A main attack is designed to capture the enemy’s position or achieve the overall objective. This type of attack usually has the majority of troops assigned to it and claims priority of supporting artillery fire. The reserve force is normally positioned to support or exploit the success of the main attack.

A supporting attack (sometimes referred to as a diversionary attack) assists the main attack by making the enemy disperse its force and fight in several locations. Supporting attacks also hold enemy forces in position, cause premature or incorrect commitments of the reserve, and confuse the enemy as to which is the main attack.

Quotes 5 and 6 are secondary sources by Carmen (Lt. Col. of the 7th New Jersey) and Cox (Brg. Gen. - 9^th Corps). Both men fought at Antietam and wrote their accounts sometime after the war. Both of them, though somewhat critical of McClellan, seem to take their versions directly from his Aug. 1863 report.

Quotes 7, 8 and 9 are from some of the most prominent historians to ever publish works on the battle.  Sears brings to light the inconsistencies in the various reports by McClellan and Harsh account provides the most detailed analysis of the plan. Of the three of them Harsh seems to be the closest to the truth, but we will come back to that later.

While certainly not an exhaustive list, all of these accounts do have one thing in common. They were all written after the fact with the benefit of hindsight.

McClellan issued no written orders at the time of the battle detailing his plan. McClellan held no council of war with his corps commanders to ensure all were familiar with what the objective was on the 17^th and what he expected of them and their men. So, whatever the exact plan McClellan had in his head on the 16^th is still unknown. In Addition, McClellan made no reconnaissance west of the Antietam with his cavalry to probe and report on the Confederate dispositions. Consequently, no report was made to the general that might provide additional insight to his thinking. Almost all of what McClellan knew of the enemy’s position was by his own reconnaissance east of the river.

As important as it is to ask what McClellan wanted to do, in order to get closer to the truth, we need to ask what did McClellan know, what did he believe and what did he eventually do. The last point being the most revealing.

First of all, McClellan knew that Harpers Ferry had fallen on the 15^th and that there was a very good chance that any forces outlined in SO 191 sent to capture it were now in Sharpsburg and available to Lee. He also knew that Lee was concentrated west of the Antietam with no apparent plans to withdraw over the Potomac or to attack him first. McClellan knew that Lee had positioned his troops in the dips and swales of the landscape to prevent any comprehensive observation from the Union side of the river and his artillery well placed. He also knew that any attack no matter the location would have to be preceded by a crossing of the Antietam.

“The Antietam was neither very wide nor very deep, but it was just enough of both that a Federal offensive in any strength would need an uncontested crossing at one of these bridges, particularly for the artillery and the ammunition trains.”[i]

By the 16^th it was also clear to McClellan that Lee intended on contesting any attempt to cross the river at and south of Boonsborough Turnpike while leaving the fords and bridge north open.

Additionally; he knew the Army of the Potomac had only existed in its current state for about a week, and it was in some cases literally being organized as it was on the march to meet Lee’s invasion. It was an amalgamation of three different armies with several of the corps commanders unfamiliar to the general commanding. It is safe to say that McClellan’s army was an unwieldly force on its best day and unmanageable one on its worse.

As for what he believed; McClellan assumed that Lee possessed a force at least as large as his own and possibly much larger; with who knows how many reserves hidden just beyond his sight. As late as the 14^th, three days before the battle, McClellan still believed he faced a sizeable force as seen from his correspondence to Halleck.

“It may, therefore, in my judgment, be regarded as certain that this rebel army, which I have good reasons for believing amounts to 120,000 men or more, and know to be commanded by Lee in person…”[ii]

McClellan was still convinced that he was facing a gargantuan force on the other side of the Creek. It has also been suggested that by the mere act of standing at Sharpsburg and offering battle, was confirmation to McClellan that Lee indeed had such a force.

By now McClellan was surely feeling the pressure of the current political situation. The Confederate invasion had set off what amounted to an existential crisis in the North. The idea of a rebel army running loose in Maryland had brought a great deal of pressure on the Lincoln administration and by extension the army. It was now it was up to McClellan to save the day and possibly the country itself. He could not disengage with Lee in the hope of getting a better opportunity to attack him at some later date. Lee had thrown down the challenge and McClellan had little choice but to answer.

Which bring us to what McClellan actually did.

The opening attack on Lee’s left began just after 5:00 am and would conclude sometime between noon and 1:00 pm. Burnside’s attack by contrast, would not begin until 10:00 am and be over by 5:30 pm.  By the end of the day McClellan would put four of his six corps (The 1st, 2nd, 6th and 12th) across the river and into attack the left, north of the turnpike; although the 6^th corps only marginally engaged late in the afternoon. That left Burnside’s 9^th corps by itself tasked with the striking the confederates on Lee’s right.  The 5^th corps was largely held in reserve, but did manage to get two brigades along with some cavalry across the middle bridge and onto the high ground beyond.  In addition, the largest part of McClellan’s artillery, including his reserve artillery was committed to supporting the assault on Lee’s left.

If we apply the principles and characteristics of the main and supporting attacks specified before the following becomes apparent. McClellan committed the largest part of his army, roughly 66% to the assault on the left; as well as the bulk of the artillery.  Reports of the number of Union guns engaged in the battle vary from 286 to 302 in 55 batteries.  At the time of Antietam most the union batteries were assigned to the various divisions.  So you don’t even have to look at a map to know at what end of the field the bulk of these guns were massed at. We must assume this was to have been the main attack or became it out of pure necessity.

Based on the many of accounts of Union corps, division and brigade commanders, many of these men who fought on the Confederate left believed that they were part of the main assault. By contrast, Jacob D. Cox commander of the 9^th corps in his account written after war was convinced that his was a supporting attack. Additionally, had McClellan intended the attack on the Confederate right to be the main attack we would and should have committed more than one Corps to it. As it was, the 9^th Corps was started way too late to really be an effective supporting attack, but that is for another article. The poor execution of the 9^th was essentially no different than of the manner in which the entire battle unfolded for the Union.

Lastly the way Lee defended the ground, had a role to play in the plan. Lee extended his line to just north of the Dunker Church and then bent it back to the Potomac. This left the ground north and east of the Confederate line perfect for the maneuvering and staging of a large infantry force. Whether or not this was part of Lee’s plan or just the only thing he could do due to the men he had on hand is debatable. I believe Lee would have defended more potential crossing points on the river north of the turnpike had he the men to do so.  He did not.

Lastly on the day after the battle General McClellan sent this in a letter to his wife:

 “The spectacle yesterday was the grandest I could conceive of; nothing could be more sublime,” he wrote. “Those in whose judgment I rely tell me that I fought the battle splendidly and that it was a masterpiece of art.”

He did not specify who volunteered that remarkable analysis’ although it seems clear, from McClellan’s perspective at least, his plan was executed precisely the way he had conceived it from the outset. [iii]

Robert E Lee would retreat back to Virginia on the 19^th thereby ending the Maryland Campaign.

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[i] Sears, Stephen- Landscape Turned Red: The Battle of Antietam (p. 169). Houghton Mifflin Harcourt. Kindle Edition.

[ii] Official Records of the War of the Rebellion: Serial 028 Page 0281 Chapter XXXI

[iii] Sears, Stephen - Landscape Turned Red: The Battle of Antietam (p. 299). Houghton Mifflin Harcourt. Kindle Edition.