High Stakes at Antietam

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It was Lee’s plan to march west from Frederick and force a battle in the broad Cumberland Valley of Maryland and Pennsylvania, pulling the Federals away from their Washington base while he drew his own supplies through the Shenandoah Valley. But despite being cut off by the Confederates’ advance, the Federals did not evacuate Harpers Ferry, guarding the mouth of the valley where the Shenandoah joined the Potomac. Lee elected to pause his campaign and sweep down on Harpers Ferry from three directions. Concealing his movements behind the bulk of South Mountain, he expected to complete the capture before McClellan realized what was going on. He issued his orders on September 9, and the next day the Confederate army left Frederick and marched off in the designated directions.

But on September 13 Lee’s best-laid plan was dangerously compromised when a Federal soldier came upon a copy of the Harpers Ferry plan, lost by a careless courier. The so-called Lost Order was soon in McClellan’s hands. In an exuberant telegram to Lincoln he announced, “I have all the plans of the Rebels 
and will catch them in their own trap … . Will send you trophies.”

The Lost Order was the intelligence coup of the war. The Confederate army was divided into five well-scattered columns, and once McClellan broke through the South Mountain passes, he would be perfectly situated to divide and conquer.

On September 14 the Confederates had just time enough to cobble together a delaying defense at Turner’s Gap and Crampton’s Gap in South Mountain. Still, Lee had decided to give up his campaign until word reached him from Stonewall Jackson that “Through God’s blessing” Harpers Ferry was in his grasp, “and I look to Him for complete success tomorrow.” Lee changed his mind and set an assembly point for his scattered army at the sleepy Maryland village of Sharpsburg, between Antietam Creek and the Potomac River.

Fully expecting the Confederates to flee back to Virginia after the beating they took at South Mountain, McClellan was surprised by a dispatch from a signal officer the next day: “A line of battle—or an arrangement of troops which looks very much like it—is formed on the other side of the Antietam creek and this side of Sharpsburg. It is four times longer on the west than on the east side of the road.”

McClellan found it too late that day to attack, and when he learned that Harpers Ferry had fallen to Jackson, he concluded that he must now be facing the entire Confederate army. “I have the mass of their troops to contend with,” he explained to Washington, “& they outnumber me when united.” So he spent September 16 arranging his forces and plotting a plan of attack. As firmly in the grip of delusion as ever, he never imagined that Lee was bluffing him on September 15–16 with hardly 15,000 men of all arms. 
The first of Jackson’s troops only began to reach Sharpsburg from Harpers Ferry on the afternoon of the 16th; at day’s end Lee was still short three of his nine divisions. Even after those three arrived on the day of battle, he had barely 40,000 troops on the field. McClellan had available to him in the Army of the Potomac 101,000 men.

The capture of Harpers Ferry netted the Confederates 12,700 prisoners, 73 pieces of artillery, 13,000 small arms, and abundant supplies—surely triumph enough for Lee to fall back to Virginia without disgrace and recalculate his plans. Instead he elected to risk a stand at Sharpsburg. He had whipped the Young Napoleon before Richmond, chased him off the peninsula, and beaten a good part of his army (along with Pope’s), at Second Bull Run. Lee was not going to be run out of Maryland before a test of arms against a general he characterized as timid.

McClellan had wasted all the opportunities inherent in the Lost Order except for this: Lee would be fighting this battle before he wanted to and not where he had first intended. For his part, McClellan would have to do battle on ground not of his choosing, and he would have welcomed more time to reorganize and refit his patchwork army. But Lee had thrown down the gauntlet in challenge, and McClellan elected Wednesday, September 17, as the day of battle.

The Confederate line roughly followed a low ridge that ran north-south down the middle of the irregular peninsula formed by Antietam Creek and the Potomac. Sharpsburg lay behind the ridge, its church steeples visible to the Federals east of the creek. McClellan aimed his primary attack against the left or northern end of the Confederate line, where the landscape of crop fields and meadows and woodlots appeared best suited for fighting. Late on Tuesday “Fighting Joe” Hooker led his First Corps across the Antietam and took up an attacking position, supported by General Joseph K. F. Mansfield’s Twelfth Corps. Farther to the south, where the landscape became steeper and more broken, Ambrose Burnside’s Ninth Corps was posted for a secondary attack. McClellan retained half his army—the Second, Fifth, and Sixth Corps—at his center east of the creek.

At first light on September 17, Hooker pushed south through a 30-acre cornfield, the East Woods on his left and the West Woods on his right. His target was the small whitewashed church of the German Baptist Brethren, called Dunkers for their baptism by total immersion, that sat on an open plateau crowded with Confederate artillery. Stonewall Jackson had turned his flank into a solid front. When the Yankees burst out of the corn, wrote a Wisconsin soldier, “a long line of men in butternut and gray rose up from the ground. Simultaneously, the hostile battle lines opened a tremendous fire upon each other. Men, I cannot say fell; they were knocked out of the ranks by dozens.” Quickly the fighting spread from the East Woods through the cornfield to the West Woods, with terrible casualties.