THE BATTLE OF ANTIETAM
17th September, 1862

McClellan's 80,000-strong army arrived at Antietam Creek on the afternoon of 15th November to find Lee with 18,000 in a strong position in front of Sharpsburg. There was no attack on the 16th as McClellan wanted a clear look at the terrain and at Lee's dispositions before attacking, which increased Lee's numbers to 26,000 when Jackson arrived at noon. When the attack started on 17th, Lee's army was still scattered, but by the end of the day, the missing divisions of McLaws, Anderson and A. P. Hill would arrive. McClellan's plan consisted of an upstream crossing by Hooker, Sumner, Mansfield and Franklin, followed by an attack on Lee's left, where Jackson was placed and a simultaneous attack on Lee's right by Burnside against Longstreet. In the event, the attacks were not well co-ordinated. Hooker was the first to attack and in spite of fierce resistance he pushed back the Confederate line. He was viciously counter-attacked and driven back by the men of Hood's division who, in the Dunker churchyard, had been having their first hot meal for days and were consequently furious at being interrupted. Mansfield then attacked along the same route. Mansfield himself was killed but his corps took and held a forward position just short of the church. Williams, now in command, sent for re-inforcements to exploit the position. Sumner's corps came up, but by a different route, and the lead division was caught in column on the flank by McLaws division (which had arrived earlier in the morning) and massacred.
This was basically the end of the attack on that flank, but Sumner's remaining two divisions pressed forward against D. H. Hill who was holding the centre with the newly arrived Anderson. Hill had a strong position in a sunken road but, due to a misunderstanding, the brigade on the left fell back and the others became open to enfilading fire and were also forced to retire. They were too weak to withstand an assault and Franklin, arriving with another five brigades, saw this and requested permission from Sumner to advance. But Sumner, still shaken by the mauling of his first division, refused and so, despite Franklin's pleas, did McClellan. This ended the attack in the centre.
On the south flank, Burnside had been trying all morning to get across the river by the bridge which was thereafter to bear his name. His four divisions were being held at bay by a single brigade under the command of Robert Toombs. It is perhaps typical of the unfortunate Burnside that he forgot to check the depth of the water by the bridge, which was easily wadeable. About one o'clock he finally stormed the bridge and in the face of this, and another division which had found a ford downstream, Toombs fell back. After more delays Burnside finally got the main attack underway at 3.00 pm and drove towards Sharpsburg. All was going well when A. P. Hill arrived after a forced march from Harper's Ferry. Hill's men had replaced their tattered uniforms with the neat, new blue ones they found at Harper's Ferry and this caused much confusion as they drove into Burnside's left flank. The attack, which had been just about to swamp Lee, was broken in the nick of time and driven back.
Casualties were heavy on this, the bloodiest day of the war being 11,000 Confederate and 12,000 Union. Strategically, the victory was McClellan's for Lee's position was impossible and he was obliged to retreat. Considering the possibilities missed for a crushing victory, however, it cannot be considered anything but a tactical failure.