Battle of Antietam

Background

By late summer 1862 the Confederacy held the initiative in the East. After beating John Pope's army at Second Manassas on 30 August, Robert E. Lee took the Army of Northern Virginia across the Potomac into Maryland from 3 September, with about 55,000 men. He hoped to find men and supplies in Maryland and to ease the strain on farms in northern Virginia, and the move coincided with Bragg's and Kirby Smith's invasion of Kentucky.

Around 9 September Lee issued Special Order 191, which split his army. Jackson, McLaws and Walker were to converge on the Union garrison at Harpers Ferry, which sat across Lee's supply line; Longstreet was to halt at Boonsboro with the trains, and D. H. Hill's division was to form the rearguard. About noon on 13 September, at a campsite outside Frederick, Corporal Barton W. Mitchell and First Sergeant John M. Bloss of the 27th Indiana found a copy wrapped around cigars. It reached George B. McClellan the same day.

McClellan now knew Lee's army was scattered, but his advance was deliberate rather than urgent; one account has him waiting some 18 hours before moving. On 14 September Confederate rearguards at Turner's, Fox's and Crampton's Gaps on South Mountain held him off for a day. Harpers Ferry surrendered on 15 September, with more than 11,000 Federal prisoners and 73 guns. That afternoon Lee drew up on a low ridge running north and south of Sharpsburg, behind Antietam Creek, which could be crossed by only three stone bridges and some fords. With the Potomac at his back, he waited for Jackson's divisions to come in.

The armies

McClellan's Army of the Potomac numbered about 87,000 men: six infantry corps under Hooker (I), Sumner (II), Fitz John Porter (V), Franklin (VI), Burnside (IX, with Jacob Cox in direct command) and Mansfield (XII), plus some 4,500 cavalry. It had roughly 275 to 293 guns. About a quarter of the army was inexperienced; half of Mansfield's XII Corps were new recruits. McClellan believed Lee's army much larger than it was, and the fear of a trap weighed on him.

Lee's army had two wings: Longstreet's five divisions and Jackson's four, and A. P. Hill's division was still at Harpers Ferry on the morning of the battle. It was also badly depleted: straggling may have cost it between a third and a half of its men, and estimates of its strength on the field run from about 37,600 to 45,000, with some 194 to 246 guns. Its advantage was the ground: a short line on a ridge behind the creek, with the Union attacks arriving one sector at a time.

The battle

The battle opened on the evening of 16 September, when Hooker's I Corps crossed the upper Antietam to find Lee's left and skirmished with Hood's division until dark. It fell into three phases on 17 September, moving from north to south, because McClellan's corps attacked one after another rather than together.

Morning, the northern sector (dawn to about 10 a.m.). At dawn Hooker's artillery opened on Jackson's men in D. R. Miller's cornfield, and his infantry advanced from the North Woods down the Hagerstown Turnpike towards the Dunker Church, a small church on high ground that both sides wanted. Hooker reported that every stalk of corn in most of the field "was cut as closely as could have been done with a knife, and the slain lay in rows precisely as they had stood in their ranks a few moments before". At about 7 a.m. Jackson was reinforced and drove the Federals back; Hood's division lost perhaps 60 per cent of its men, the Louisiana Tigers 323 of 500, and the 12th Massachusetts two-thirds of its strength, the heaviest regimental loss of the day. Hooker's corps lost some 2,500 in two hours, and Hooker was shot in the foot. Around 8 a.m. Mansfield's XII Corps attacked through the East Woods; Mansfield fell mortally wounded, but by 9 a.m. his men had regained ground near the church. The Cornfield is said to have changed hands about fifteen times. Sumner then sent Sedgwick's division, 5,400 strong, into the West Woods. Confederate troops struck both its flanks and it lost more than 2,200 men in under half an hour. Losses in the northern sector that morning approached 13,000.

Midday, the centre (9.30 a.m. to 1 p.m.). French's division of Sumner's corps, moving up behind Sedgwick, veered south across the Roulette farm into D. H. Hill's division, posted in a sunken farm lane between the Roulette and Piper farms. French lost 1,750 of 5,700 men in under an hour, and the Irish Brigade of Richardson's division lost 540. Around noon Richardson's men worked onto the flank of the lane and broke the Confederate line. The road, filled with dead, became Bloody Lane, and some 5,000 or more men fell around it. The Confederate centre was open, but Richardson was mortally wounded, Hancock took over a spent division, and the fighting in the north and centre died away in confusion and exhaustion.

Afternoon, the southern sector (1 p.m. to 5.30 p.m.). Burnside's IX Corps had been trying since mid-morning to cross the Lower (Rohrbach) Bridge, held by about 400 Georgians under Robert Toombs on the bluffs above it. The Federals took the bridge at about 1 p.m., having lost more than 500 men to the defenders' fewer than 160, and then spent two hours re-forming. At about 3 p.m. more than 8,000 men with 22 guns advanced over the hills towards Sharpsburg, driving the Confederates back almost to the town and threatening Lee's line of retreat to Boteler's Ford. Then A. P. Hill's division, left behind at Harpers Ferry to deal with the captured property, came onto the field between 3.30 and 4 p.m. and struck Burnside's exposed left flank; Gregg's brigade hit the 16th Connecticut, which lost 185 men. The IX Corps fell back to the heights near the bridge, having lost about a fifth of its strength. Porter's V Corps and much of Franklin's VI Corps, together over 20,000 men, stayed in reserve all day. By 5.30 p.m. the fighting was over.

Aftermath

In some twelve hours the Union lost about 12,400 men and the Confederates between 10,300 and 10,700, some 22,700 in all: the bloodiest single day in American history. Generals Mansfield, Richardson and Rodman were killed or mortally wounded on the Union side, Branch and Starke on the Confederate. Clara Barton brought supplies to the field hospitals.

Tactically the battle was a draw. Lee held his ground through 18 September while removing his wounded, then recrossed the Potomac that night; McClellan, with fresh corps unused, did not renew the attack, and a cautious pursuit was checked at Shepherdstown. Strategically it was a Union success. Lee's invasion was over, and Lincoln, who had been advised to wait for a victory before acting on emancipation, issued the preliminary Emancipation Proclamation on 22 September, declaring free from 1 January 1863 the enslaved people in states still in rebellion. The war now aimed at ending slavery as well as saving the Union, and Britain and France held back from recognising the Confederacy. McClellan stayed idle until late October; Lincoln removed him in early November.

Antietam was also the first American battlefield photographed before the dead were buried. Alexander Gardner and James Gibson took about a hundred photographs, the first photographs of Americans killed in battle, and public interest in them was intense. Historians still argue over McClellan's use of the Lost Order and how close he came to destroying Lee's army.

Wargaming it

Antietam is a big battle on a small field, which makes it unusually playable. A division- or corps-level game with brigades as units fits a table, while each of the three phases makes a self-contained scenario at regimental scale: the Cornfield and West Woods, Bloody Lane, or Burnside's Bridge and the final attack.

The terrain does a lot of work. Antietam Creek can be crossed only at three bridges and a few fords, the Dunker Church plateau and the woods around it decide the north, the Sunken Road is a ready-made trench that becomes a trap once flanked, and the bluffs above the Lower Bridge let a few hundred riflemen hold off a corps.

The interest is in command. A free-handed Union player will attack everywhere at once and probably win, so the historical game needs rules that release Union corps one after another and hold back Porter and Franklin, while the Confederate player shifts thin reserves from crisis to crisis. A. P. Hill's arrival between 3.30 and 4 p.m. should be uncertain in time and place. The what-ifs are clear: Burnside across by mid-morning, Porter's corps committed against the broken centre, or a Lost Order never found and Lee's army reunited before battle.

Maps and pictures