Battlefield Chronicles: The Battle of Antietam

The Battle of Antietam is long remembered as the bloodiest day in U.S. military history. More than 3,500 men were killed at Antietam, more than 17,000 were wounded, and thousands more were missing or captured by the end of the fight. 

It shouldn't have been this way. ​​Before the two sides met near Antietam Creek on September 17th, 1862, two Union soldiers discovered the entire enemy battle plan wrapped in a bunch of cigars. Union Gen. George B. McClellan had the chance to knock out each part of Confederate Gen. Robert E. Lee's divided Army but didn't.

Although the outcome was technically a win for the Union, as they repelled a Confederate invasion of the north, the battering both sides took for such a small tactical victory seems disproportionate even today. Robert E. Lee's Army of Northern Virginia was forced to abandon this particular invasion of the north, but there would be others. 

The question remains, why was Antietam so bloody? 

By the Autumn of 1862, the Civil War was not going well for the Union. Following up on a victory at the Second Battle of Bull Run, Lee invaded Maryland on September 3rd, assuming Marylanders were sympathetic to the Confederate cause. They were wrong. 

When the Army of the Potomac came marching through the streets of Maryland towns and cities, it was cheered and welcomed. To make matters worse, the 87,000-strong Union Army dwarfed the size of Lee's 55,000 men. Confederate leaders, determined to gain European recognition, demanded a significant victory on Union soil, so Lee marched anyway.

When the two sides met, the rebels were positioned behind the creek, covered by stone fences and natural defenses that provided cover. The only problem was its only line of retreat was blocked by the Potomac River. Moreover, the rebel Army numbered only 18,000, just as the battle plan said it would. 

The Union Army, now three times the size of the Confederates, might have been swept away had McClellan launched an attack at the earliest possible time, but he was afraid it was a trap and thought Lee had 100,000 men in reserves nearby. He waited two days to begin the fight, which gave the Confederates ample time to build defenses and for two more divisions to arrive on the battlefield. 

When the attack did come, McClellan planned to overwhelm the rebel left flank with overwhelming numbers. Watching the Union Army move into position, Lee realized what would happen and reinforced his left flank. A series of critical errors on McClellan's part would turn the battle into a meat grinder. Rather than launch a coordinated assault against the rebels, McClellan, who oversaw the battle from nearly a mile away, essentially executed three separate attacks.

In the morning, the Union forces assaulted the northern end. Gen. Joseph Hooker led the assault of an equally-matched force under Confederate Gen. Thomas "Stonewall" Jackson. An artillery duel broke out in the early morning, followed by a bloody stalemate between the two sides. After two hours, not much of the cornfield changed hands. 

As more and more reinforcements from both sides poured into the battle, they were gunned down in turn by enemy troops. The Union attack here was as uncoordinated as the overall strategy. By 10 in the morning, 13,000 men were casualties. 

At midday, the fighting moved to the center of the line, which was fighting from a sunken road that formed a natural trench against an attack. A series of three attacks over the course of an hour against the sunken road caused more than a thousand casualties. It wasn't until the fifth Union assault that the Confederate began to buckle. The Federal troops advanced far enough to form an enfilade against the men in the makeshift trench. 

Though an artillery barrage briefly lifted the enfilade, the Union forces broke the rebel center. It was an opportunity to split the Confederate line in two if the Union pressed its advantage - but McClellan did not support pressing the advantage. After 1 in the afternoon, the fighting shifted south once more. Five thousand men were casualties in the center. 

The main attack was still in the north on the rebels' left flank, but McClellan called for an attack in the south to move Confederate forces away from the northern area. For most of the morning, Gen. Ambrose Burnside had been attempting to capture a key bridge, despite outnumbering the Confederate defenders in the area four to one. 

When they finally took the bridge, it became a bottleneck for Union troops crossing the river. They forgot to bring ammunition for the cannons, wagons had difficulty navigating the bridge, and the whole mess took two hours, giving the Confederates enough time to retreat and call up reinforcements from other areas - including Harper's Ferry, some 17 miles away. 

The green troops at the head of the Union advance broke and ran in the face of the new Confederate troops. Newly-arrived rebels enveloped the leading elements under Gen. A.P. Hill. Burnsides' men were forced back to the bridge. 

By 5:30 p.m., it was all over. The piecemeal attacks on Lee's rebel Army allowed the general to shift his troops all day to support the bulk of the fighting where it was taking place. He mounted a defense that his limited resources of men and materiel shouldn't have been able to in an orchestrated assault. 

The result was the bloody stalemate at Antietam that caused more than 22,000 casualties on both sides. The rebel Army was as battered as the Federal force and would have to retreat into Virginia, giving the victory to the Union. However, more victories like the one at Antietam might have cost the Union the war.