Battle of Antietam (1862): America's Bloodiest Single Day

The Battle of Antietam, known in the South as the Battle of Sharpsburg, was fought on 17 September 1862 along Antietam Creek near Sharpsburg, Maryland. With about 23,000 men killed, wounded or missing, it remains the bloodiest single day in American history. The battle ended Robert E. Lee’s first invasion of the North and gave Abraham Lincoln the opportunity to issue the preliminary Emancipation Proclamation.

Background: Lee invades Maryland

The summer of 1862 had gone badly for the Union in the East. Lee’s Army of Northern Virginia drove George B. McClellan’s Army of the Potomac away from Richmond in the Seven Days Battles, then routed John Pope’s army at the Second Battle of Bull Run at the end of August, on almost the same ground as the First Battle of Bull Run a year earlier.

Lee decided to carry the war north. In early September his army crossed the Potomac River into Maryland, a slave state that had stayed in the Union. He hoped to feed his men from Northern farms, draw Union forces out of war-ravaged Virginia, encourage pro-Confederate Marylanders and influence the Northern midterm elections. A major victory on Union soil might also persuade Britain and France, which were then discussing mediation, to recognise the Confederacy.

Lee boldly divided his army. He sent Stonewall Jackson with about half of it to capture the Union garrison at Harpers Ferry, which blocked his supply line through the Shenandoah Valley, while the rest moved west across South Mountain.

The lost order

On 13 September 1862, near Frederick, Maryland, Corporal Barton W. Mitchell and Sergeant John M. Bloss of the 27th Indiana found a copy of Lee’s Special Order 191 wrapped around three cigars in an abandoned Confederate camp. It revealed that Lee’s army was scattered across the countryside. McClellan reportedly told a subordinate that with this paper he could whip Lee.

McClellan moved faster than usual but still cautiously. On 14 September his troops forced the passes at the Battle of South Mountain, but the delay gave Jackson time. On 15 September Harpers Ferry surrendered with about 12,500 Union soldiers, the largest surrender of US troops during the Civil War. Lee gathered his army behind Antietam Creek at Sharpsburg, with the Potomac at his back.

The armies

McClellan had about 87,000 men present, though he believed, as usual, that he was heavily outnumbered. Lee had perhaps 35,000 to 40,000, and some of Jackson’s men were still on the road from Harpers Ferry. McClellan spent 15 and 16 September preparing, allowing Lee to concentrate. His plan was to attack the Confederate left, then the right, and finally break through in the centre, but in practice his corps went in one after another, allowing Lee to shift troops to meet each blow.

The battle

Morning: the Cornfield and the West Woods

The battle began at dawn on 17 September when Major General Joseph Hooker’s I Corps attacked south down the Hagerstown Pike towards a small whitewashed church of the German Baptist Brethren, known as the Dunker Church. Between Hooker and the church lay David Miller’s 24-acre cornfield.

For three hours the Cornfield changed hands repeatedly as Union and Confederate units charged, counter-charged and were cut down by artillery and musket fire. A Confederate counter-attack by John Bell Hood’s division, including the Texas Brigade, threw back Hooker’s men at terrible cost. Union XII Corps commander Joseph Mansfield was mortally wounded. Hooker himself was wounded in the foot and carried from the field.

Around 9 a.m. John Sedgwick’s division of Edwin Sumner’s II Corps advanced into the West Woods without proper reconnaissance. Struck from three sides, it lost more than 2,000 men in well under an hour. By mid-morning the fighting on the northern part of the field had died down in exhaustion, with neither side gaining a decisive advantage.

Midday: the Bloody Lane

The fighting shifted south to the centre of the line. There Confederate troops under D. H. Hill held a sunken farm road, worn down by years of wagon traffic, which formed a natural trench. From about 9:30 a.m. Union divisions under William French and Israel Richardson, including the famous Irish Brigade, attacked in successive waves.

For more than three hours the Confederates held, but a misunderstood order led part of their line to withdraw, and Union troops reached positions from which they could fire down the length of the lane. The road filled with dead and wounded and became known as the Bloody Lane. Roughly 5,500 men from both sides became casualties in this part of the battle. Richardson was mortally wounded, and the Confederate centre was badly shaken. Yet McClellan, who kept two corps in reserve, declined to commit them to exploit the opening.

Afternoon: Burnside’s Bridge and A. P. Hill

On the southern end of the field, Major General Ambrose Burnside’s IX Corps had been ordered to cross Antietam Creek at the Rohrbach Bridge, a narrow stone bridge. A few hundred Georgians under Robert Toombs, firing from the wooded bluff above, held off repeated Union attacks for hours. The bridge, ever since called Burnside’s Bridge, was finally taken at about 1 p.m., while other Union troops found a ford downstream.

Burnside needed another two hours to reorganise and resupply before advancing on Sharpsburg. By mid-afternoon his troops were pushing back Lee’s thin right flank and threatening to cut off the Confederate line of retreat to the Potomac. At that moment, at around 3:30 to 4 p.m., Major General A. P. Hill’s Light Division arrived after a forced march of about 17 miles from Harpers Ferry and struck Burnside’s exposed left flank. The Union advance collapsed and fell back towards the creek. Darkness ended the fighting.

By the numbers

Figures are standard estimates; Confederate returns in particular are incomplete, and many of the wounded later died of their injuries.

Aftermath

On 18 September the two battered armies faced each other without renewing the battle. That night Lee withdrew across the Potomac into Virginia. McClellan, despite fresh troops and orders urging him on, did not pursue effectively. Lincoln visited the army in early October and grew increasingly frustrated, and on 5 November 1862 he removed McClellan from command, replacing him with Burnside, who led the army to disaster at the Battle of Fredericksburg that December.

The town of Sharpsburg, its churches, barns and homes were turned into makeshift hospitals. Among those caring for the wounded was Clara Barton, who later founded the American Red Cross. In October 1862 photographs of the dead taken by Alexander Gardner and James Gibson were exhibited at Mathew Brady’s gallery in New York under the title The Dead of Antietam. They were the first images of American battlefield dead seen by the public, and they brought the reality of the war home to Northern civilians.

Antietam and emancipation

The most important consequence was political. In July 1862 Lincoln had told his cabinet that he intended to free the slaves in rebel territory, but Secretary of State William H. Seward advised waiting for a victory so that the move would not look like desperation. Antietam, though not a decisive triumph, was enough. On 22 September 1862 Lincoln issued the preliminary Emancipation Proclamation, announcing that enslaved people in states still in rebellion on 1 January 1863 would be “then, thenceforward, and forever free”.

The proclamation changed the character of the war. Preserving the Union was now joined to ending slavery, and the Emancipation Proclamation that took effect on 1 January 1863 also opened the way for Black men to serve in the Union army. In Britain, where slavery had been abolished in 1833 and public opinion was strongly anti-slavery, the government stepped back from plans to mediate. Foreign recognition of the Confederacy never came.

Myths and facts

• Myth: Antietam was a clear Union victory. Fact: On the battlefield it was a bloody stalemate; its significance lay in Lee’s retreat and the political opportunity it created.
• Myth: The lost order guaranteed Union success. Fact: It gave McClellan an extraordinary advantage, but his caution and piecemeal attacks allowed Lee to escape destruction.
• Myth: Antietam produced more deaths than any other Civil War battle. Fact: Multi-day battles such as Gettysburg had higher total losses; Antietam is the bloodiest single day.

Timeline

• 1862, 4-7 September: Lee’s army crosses the Potomac into Maryland.
• 1862, 13 September: Union soldiers find Special Order 191 near Frederick.
• 1862, 14 September: Battle of South Mountain.
• 1862, 15 September: Harpers Ferry surrenders to Jackson.
• 1862, 17 September, dawn: Hooker attacks through the Cornfield.
• 1862, 17 September, midday: Fighting at the Bloody Lane.
• 1862, 17 September, afternoon: Burnside’s Bridge is taken; A. P. Hill’s arrival halts the Union advance.
• 1862, 18-19 September: Lee withdraws across the Potomac.
• 1862, 22 September: Lincoln issues the preliminary Emancipation Proclamation.
• 1862, 5 November: Lincoln removes McClellan from command.

Why it matters

Antietam was the turning point that was not quite a victory. It stopped the Confederacy’s first invasion of the North, discouraged European intervention and allowed Lincoln to make the destruction of slavery a Union war aim. Its terrible cost foreshadowed the battles still to come, from Fredericksburg to the Battle of Gettysburg, and Antietam National Battlefield remains one of the best-preserved Civil War sites in the United States.