| Battle of Antietam | |||||||
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| Contenders | |||||||
 United States (Union) |
 Confederate States |
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| Military Leaders | |||||||
| George B. McClellan | Robert E. Lee | ||||||
| Unit Strength | |||||||
| 75,500 | 38,000 | ||||||
| Casualties and Deaths | |||||||
| Total: 12,401 | Total: 10,316 | ||||||
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2,108 killed 9,540 wounded 753 captured/missing |
1,546 killed 7,752 wounded 1,018 captured/missing |
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| Part of the American Civil War | |||||||
The Battle of Antietam took place between Union and Confederate troops on September 17, 1862 during the American Civil War. The encounter took place near Sharpsburg in Maryland (it is often referred to as the Battle of Sharpsburg) and Antietam Creek.
The Union Army of the Potomac was led by Major General George B. McClellan, while the Confederate commander of the Army of Northern Virginia was General Robert E. Lee. The battle took place during the Maryland Campaign and was the first time in the Civil War that the opposing forces had met in Union territory.
Events Leading up to the Battle
After the Confederate victory at the Second Battle of Bull Run, General Lee decided to press home his advantage and take the offensive by marching into Union territory. He decided to lead his forces into Maryland, where he thought he would gain support from the local people, whom he thought were against President Abraham Lincoln’s reforms.
Lee divided his army into separate units. He located one unit in Hagerstown, Maryland, and sent another to attack the Union garrison at Harper’s Ferry in West Virginia. Lee’s plan and full details of how his forces were dispersed became known to McClellan, but the commander failed to take any action based on the information until it was too late. By the time McClellan moved, some 18 hours later, the Confederates had had time to consolidate their positions. Lee had installed his troops in solid defensive positions around Antietam Creek.
Meanwhile the unit sent to Harper’s Ferry, under the command of Major General Stonewall Jackson, was successful in taking the garrison. McClellan had to advance through the Blue Ridge Mountains, and his forces met strong resistance from Confederate positions at two passes in the Battle of South Mountain. While the Union army was successful in driving back the opposition, the extra delay gave Lee even more time to organize his defenses at Sharpsburg.
The Battle Strategy
McClellan’s Army of the Potomac had been augmented by forces from the Army of Virginia and when they arrived in the area on September 15, they outnumbered confederate forces by three to one. It is almost certain that had they pressed ahead, they would have routed Lee’s army.
The position of Lee’s main force near Sharpsburg was not impossible to overcome. Antietam Creek was not a serious obstacle to a Union attack, and was narrow enough and shallow enough in places to make it possible to cross without bridges. On top of this, Lee would have found it difficult to retreat. The Potomac River cut off a full retreat to the rear because the Confederates would be able to use just one location for crossing.
By this time, detailed information about Lee’s troop positions had fallen into McClellan’s hands, but it is thought he completely overestimated the number of Confederate troops present. His decision to exercise caution meant that Lee’s troop numbers were boosted by the arrival of most of Jackson’s men from Harper’s Ferry, as well as the troops who had initially been sent to Hagerstown.
Influenced by the locations of bridges on the Antietam Creek, McClellan’s strategy was to concentrate his assault on the Confederate’s left flank and he planned to use more than half of his entire force to achieve this objective.
On September 16, he sent an expeditionary force, under the command of Major General Joseph Hooker, across the Creek to engage the enemy. Lee correctly guessed that this attack on his left flank was not a diversionary tactic, but that it indicated where McClellan intended to focus his offense, and he set about reinforcing the flank.
Union Lack of Coordination
McClellan made a huge tactical mistake in not advising his officers of his overall plan. Instead, he only informed the officers of what was expected from their own troops. The lie of the land meant that each section was unable to see what was happening in other areas, and communication between McClellan’s command post and the three separate offensive locations were poor.
Instead of launching his three offensives at the same time, McClellan launched the first attack in the morning, the second at midday, and the third later in the afternoon. This poorly executed strategy gave Lee the opportunity to concentrate his forces at the focus of each attack, and cancelled out the Union army’s advantage of numerical superiority.
The Federal Offensives
The first Federal offensive began at 5.30 in the morning, and a pitched battle followed until about 10am, after which the Union forces had managed to gain some ground, but suffered heavy casualties, as did the Confederate defenders.
The second Union offensive, an attack on the Confederate center, was launched at midday. Further bloody fighting ensued, with heavy casualties on both sides. During this phase, McClellan once again failed to use his numerical advantage. He had the opportunity to move more of him men into the attack. Had he done so, he could have split the Confederate forces in two, but he failed to take the opportunity.
The third offensive took place mainly in the afternoon, with Union forces led by Major General Burnside crossing the Antietam. Burnside seems to have adapted McClellan’s cautious approach, and he too failed to make a significant impact on the Confederate forces. Problems with supplies meant Burnside had to pause his attack, once again allowing the Confederates time to strengthen their defenses.
Confederate reinforcements had arrived, and had repelled various Union forays. Burnside decided to hold his position defending the bridge they had used to cross the Antietam. On September 18, a truce was declared to allow recovery of dead and wounded soldiers, and the battle came to an end. Lee used this opportunity to begin withdrawing over the Potomac to Virginia.
Casualties
The casualty figures were very high on both sides, the Federal army suffered 2,108 fatalities out of a total of 12,401 casualties, while 1,546 Confederates died out of a total of 10,318 casualties.