Streetwise Professor

September 17, 2022

Antietam at 160

Filed under: Civil War,History,Military — cpirrong @ 12:39 pm

Today is the 160th anniversary of the Battle of Antietam (Sharpsburg to the Confederates). As is widely known, it was the bloodiest single day in American history.

Charge of the 1st Texas, The Cornfield, Antietam

What is remarkable is that although the casualties on 17 September 1862 were the largest in American history, the armies were relatively small. Both had experienced substantial wastage in the Second Manassas Campaign, in the march into Maryland, and in the Battle of South Mountain. By the time the Army of the Potomac and the Army of Northern Virginia reached Sharpsburg on 16 September, the Federals numbered only about 65,000 and the Confederates somewhat south of 40,000 (with 37,500 being a common estimate).

Meaning that relatively small armies absorbed the massive casualties. (By contrast, at Gettysburg Lee’s army was around 75,000 strong, and Meade’s probably 10,000 more).

Confederate casualties are usually given as 10,300, which amounts to a percentage loss of 27.5 percent. When accounting for the fact that about 20,000 Union troops (of the V and VI Corps) were only slightly engaged, the Federal percentage loss is similar. The bulk of the fighting was done by the I, II, IX, and XII Corps, which amounted to around 46,000 men (not much more than Lee, and certainly not a large enough margin to overcome the defender’s usual advantage) that suffered 11864 casualties, or about 26 percent.

Interestingly, though high, these percentages do not match Stones River or Chickamauga, although those were admittedly 2 day battles.

Like many Civil War battles, Antietam is the subject of considerable controversy. Should Lee have invaded in the first place? Once he invaded, and learned that McClellan was hot on his heels, should he have fought the battle where he did, or withdrawn to Virginia? How was McClellan’s generalship? And of course there are many subsidiary controversies.

On the first, it’s a close call. Given what he knew at the beginning of September, there were defensible reasons for Lee to take the offensive to Maryland: exploiting the initiative and the momentum from Manassas, the apparent chaos in Union ranks after the Manassas debacle, the possibility of recruiting in Maryland (which of course came a cropper but Lee could not have known that in advance), giving northern Virginia a chance to recover from Yankee occupation (and depredations), influencing the fall of 1862 congressional election. Against all that was the exhausted state of the Army of Northern Virginia, which had been fighting and marching intensely since the end of May. The march into Maryland only exacerbated that exhaustion and the slow bleeding of his ranks–something that Lee should have been able to predict. He did not, perhaps because a form of what the Japanese called “victory disease” had given him the perception that his men were superhuman.

Once in Maryland, the decision to fight on the banks of Antietam Creek is far less defensible, especially once Lee had learned of McClellan’s unexpected speed in reconstituting shattered Union formations and moving west to confront Lee. Lee courted catastrophe by fighting with his back against the Potomac, with a tired and diminished force. He escaped disaster by only the thinnest of margins.

Which brings us to McClellan, who is largely responsible for Lee’s escape. The Union general is always a lightning rod, and he has intense partisans for and against at Antietam in particular. My view is that his conduct of the campaign up until early on the 17th of September was quite creditable, and somewhat atypical. He did move with relative alacrity: whether the “Lost Order” and its disclosure of Lee’s distributions was the cause of McClellan’s unaccustomed aggressiveness will never be resolved. His assembling a fighting force from the hodgepodge of defeated and demoralized units from two armies (his Army of the Potomac and Pope’s Army of Virginia) is quite remarkable.

His plan on the morning of the 17th was understandable, and somewhat conventional in that (like Lee on 2 July 1863 at Gettysburg) he ordered an en echelon attack, with the left attacking first, then the center, then the right. (Civil War commanders seemed to favor the echelon attack, despite its repeated failure.) In the event, however, this gave Lee the opportunity to shift troops from one sector of his front to those under direct threat: the near destruction of Sedgwick’s division by units that Lee frantically shifted from his center and right is the best example of this. A simultaneous attack would have increased the odds of success.

Moreover, McClellan’s hands-off approach to the battle contrasts poorly with Lee’s decisive hands-on generalship. For most of the day, McClellan was a spectator watching from the Pry House while his units fought essentially three separate and uncoordinated battles on the left, center, and right. In contrast, Lee imposed his will and personally pushed divisions to where they were desperately needed when they were needed.

McClellan’s distant approach is even less defensible given that he was working with subordinates and units with whom he was unfamiliar in their current roles, or whom he had considerable cause not to delegate control to. On the left, Hooker was new in command to the I Corps, which had been under the Army of Virginia and which McClellan had never seen in action. Also on the left, the XII Corps was another ex-Army of Virginia unit under a commander (Mansfield) that had never led any unit, let alone a corps, in the field. In the center, the II Corps was commanded by “Bull” Sumner, of whom it was said bullets would bounce off his hard head. McClellan knew Sumner to be brave, but totally unsuited for autonomy on the battlefield. Burnside was an old friend of McClellan (though they would be estranged after Antietam), but he too had never commanded a large formation in a major battle anywhere, let alone under McClellan’s eye. What’s more, none of these Corps commanders had worked with each other before.

So McClellan had ample reason to realize that the Army of the Potomac and its corps commanders needed close supervision and could not just be turned loose to execute a plan while he watched from afar. Yet watch from afar he did.

Moreover, whereas Lee used every man–and used many men at multiple points on the battlefield–two of McClellan’s major units–V and VI Corps, ironically commanded by McClellan’s “pets” Porter and Franklin–remained largely idle the entire day. Based on numbers compiled by Antietam historian (and battle veteran) Ezra Carmen, only about 30 percent of those units saw action, and even those did not engage in intense fights: those engaged suffered less than 10 percent casualties.

Even though Lee’s center was virtually naked in the afternoon, I am skeptical that a push by Porter’s Corps would have resulted in a disaster for Lee’s army: space/time factors meant that any such attack would have lost force in or shortly beyond Sharpsburg itself even if it had pushed Lee off the Sharpsburg ridge. But “putt[ing] in all your men” (as Lincoln told Hooker when he assumed command of the Army of the Potomac, no doubt with the memory of Antietam in mind) would have greatly increased McClellan’s odds of achieving a more decisive victory than he did–especially if he had put them in all at once.

By the time the sun set on America’s bloodiest day, the outcome on the field was a stalemate. But it was arguably the most decisive and important drawn battle in history. For Lee was forced to withdraw across the Potomac, and that gave Lincoln enough of a claim to victory to issue the Emancipation Proclamation, which changed not just the trajectory of the Civil War, but of American history.

I’ve written before that I have visited Antietam dozens of times, and that it is my favorite battlefield. I can’t be there today except in memory. If you have been there, or even if you haven’t, it is worth spending a moment to remember the carnage in the pastoral countryside of western Maryland, and the weighty history birthed by the death of so many.

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  1. My knowledge of your War of Southern Secession is skimpy. Did both sides use conscription?

    Comment by dearieme — September 20, 2022 @ 8:36 am

  2. Both sides resorted to conscription during the US Civil War. It was introduced earlier and done more widely in the Confederacy because it had far less manpower. Both sides’ armies were overwhelmingly volunteer though.


    Comment by Chris — September 20, 2022 @ 11:18 am

  3. 1. One aspect of your analysis of Lee’s reasoning for moving across the Potomac that you are missing is that the initial phase of the campaign was designed to isolate and surround the garrison at Harper’s Ferry.

    2. Lee had to gather his scattered commands that were north of the Potomac after South Moutain. That is almost certainly why he was still north to offer battle at Sharpsburg.

    3. The Union assault was clearly not an en echelon attack. Both wings were supposed to attack on a more simultaneous basis.

    4. The reason for en echelon attacks in the Civil War (and other wars) is that in the limited communications of the era it was the easiest way of controlling your attack. When the unit to the left or right of you moved, then you moved. It was a Napoleonic tactical maneuver with the main intention of moving the opponent’s reserve forces to one area and then assaulting weakened sectors.

    5. One way of understanding McClellen’s failure as a tactical commander, the weakest sector of the Confederate line was directly across from his headquarters, He could have used elements of the V Corps to flank the Rebel positions in the Bloody Lane. A coordinated attack by French, Richardson, and one or more of the V Corps divisions would have destroyed the center. This tactical coordination simply was lacking.

    Comment by MARK — September 24, 2022 @ 2:36 pm

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