If you haven’t already, please read my previous post: Battle Spotlight #8: Antietam: Part 1 – Introduction.
Preparations for Battle
On September 16, Generals Lee and McClellan spent the whole day maneuvering and positioning troops. Lee took a defensive stance on the west side of Antietam Creek, positioning Longstreet’s corps in a strong position in a straight line running from a little north of the town of Sharpsburg to the Lower Bridge, with his right anchored on the Antietam. Antietam Creek has three bridges: the Upper Bridge, which is about two and a half miles northeast of Sharpsburg; the Middle Bridge, a mile directly east of Sharpsburg; and the Lower Bridge, known as the Rohrbach Bridge by the locals and later called the Burnside Bridge, less than a mile southeast from Sharpsburg.
As Stonewall Jackson’s troops arrived from Harper’s Ferry, Lee deployed them on very valuable high ground north of Sharpsburg, anchored on the Potomac. McClellan, meanwhile, sent Hooker’s I Corps across the Antietam to probe the enemy positions. Meade’s division skirmished with Hood’s Confederate division near the East Woods. Lee’s entire battle line measured about 4 miles long.
As artillery batteries continued to duel, McClellan formed his own battle plan. He planned to overwhelm the Confederate left (northern) flank. He chose this position because of the positions of the bridges on the Antietam: the Lower Bridge was overlooked by steep bluffs, which were occupied by a considerable amount of Rebels who could mow down whoever crossed the bridge. If he considered crossing the Middle Bridge, the troops would be subject to massive artillery fire on the eastern side of Sharpsburg. But the Upper Bridge was two miles east of Confederate batteries and could be safely crossed.
His plan was simple: attack the Confederate left with two corps, supported by two more, make a diversionary attack on the Confederate right with a fifth corps, and if either attack succeeded, attack the center with his reserves.
This plan was brilliant, and it might have been carried out, had it not been for a simple mistake: when issuing orders to his corps commanders, McClellan only gave them their own orders for their specific corps and not the entire battle plan. On the day of the battle, the terrain made it hard for corps commanders to see what was going on outside their general areas, and since McClellan was headquartered at the Pry House, east of the Middle Bridge, it was difficult even for him to coordinate the various corps. The result: chaos and poorly executed commands which led to the battle degenerating into three separate, smaller, and uncoordinated battles – the morning phase in the northern end of the battlefield, midday in the center, and afternoon in the south.
All of this led to confusion in the battlefield, and it allowed time for Lee to shift his forces to meet each attack as it happened – virtually eliminating the two-to-one advantage the Union forces had over the Confederates.
Except for long-range artillery duels, all was quiet during the 16th. But that was about to change the next day…
Please read my next post: Part 3 – Early Morning for a continuation of the story of the Battle of Gettysburg!