The bloodiest day in U.S. military history

While most would assume that America's bloodiest day came in one of the larger conflicts, like World War I or II, the U.S. lost more troops on Sep. 17, 1862, when Union troops found the plans for Gen. Robert E. Lee's ongoing invasion of Maryland. Approximately 23,000 men were killed and wounded in the one-day clash.

(Author's note: This article contains photos from the Antietam battlefield in the days immediately following the fighting. Some photos contain the images of the brave men who died that day.)

The bridge over Antietam Creek where much of the bloodiest fighting took place.

(Library of Congress)

The road to Antietam began when Lee marched his troops across the Potomac and into Union-aligned Maryland while attempting to influence the midterm elections of 1862. He was hopeful that a few decisive Confederate victories on Union soil could cause a surge in votes for candidates opposed to the war, potentially leading to the start of peace negotiations at home. He also had a shot at diplomatic recognition of the Confederacy from European powers, like England and France.

Lee captured Frederick, Maryland, and then split up his force, sending four units against four towns. But, importantly, that left Frederick empty, and Union Gen. George C. McClellan moved in to collect what intel and supplies they could find. There, they found Lee's entire battle plan. According to legend, the plan was wrapped around three cigars.

So, a cigar for the soldier who found it, a cigar for the sergeant who was with him, and a cigar for the general who was left with wet pants after how excited he got when he saw Lee's entire Special Order 191, complete with all details.

But McClellan wasn't exactly the most decisive and bold of commanders, and he waited a full 18 hours to get on the move, allowing Confederate forces to create a defensive line that delayed him further. By the time he was able to reach Lee, the Confederate Army was already coalescing. Lee was preparing for the Union attack he knew was coming.

Still, McClellan was headed for Lee with over 75,000 troops while Lee would start the battle with less than 40,000 troops and, even if all of his nearby troops made it to the battle within the day, he would still have less than 50,000. McClellan's forces were in relatively good shape while Lee had many who were sick and exhausted.

While nothing about Antietam Creek, located near Sharpsburg, Maryland, was of true strategic value, both commanders knew that the moment was crucial. Keeping France and England on the sidelines required a Union victory, while the Confederates needed a huge win to influence the Union elections.

The fighting started in a cornfield near Dunker Church. 10,000 men were killed and wounded in rifle and artillery fire so heavy that it cut the corn, originally higher than a man's head, clear to the ground.

(Library of Congress)

When Sep. 17, 1862, dawned, 1,000 Union troops slipped through a cornfield toward Confederate lines, seeking to get the jump on Georgia soldiers on the other side. Unfortunately for them, the Georgians were expecting the move, and were laying on the ground with their weapons ready.

When the Union troops emerged, the Georgians hopped up and immediately started cutting down the men in blue.

Artillery fire crisscrossed the field and waves of troops from each side tried to cross the field to shut down their foes. Confederate defenders held their ground at Dunker Church. By the time it was finished, 10,000 soldiers were killed and wounded. Some units suffered losses of 50 to 70 percent — and it was only mid-morning.

In a weird fluke of history, the unit that had found Special Order 191 and made the battle possible was one of those hit hardest in the cornfield.

As the fighting for the cornfield and church reached its zenith and then tapered off, Union Forces maneuvered toward the Confederate center and found an old road used by wagons which, due to traffic and weather, had eroded to such a point that sections of the road were five feet below the surrounding ground.

Thousands of Confederates waited in breastworks, as well positioned and defended as if it were a deliberate fort. Their first volley nearly eradicated the first row of Union troops and the fight for the Sunken Road was on. Union forces marched toward the road over and over again.

The "Sunken Road" was a depression caused by vehicle traffic and erosion that created an easy fortress for Confederate troops, at least until Union soldiers were able to flank them. 5,500 men are thought to have been killed and wounded in the fighting there, earning it the nickname the "Bloody Lane."

(Library of Congress)

Finally, blue uniforms nearly surrounded the desperate men in grey whose low-lying fort became a barrel, leaving them to play the part of fish. Some were able to flee to the rear, but most of the 2,000 defenders were cut down and their bodies piled up. The Sunken Road would later be described with another name, "The Bloody Lane."

While the cost to both sides was great, the capture of the Bloody Lane collapsed Lee's center. A decisive thrust at this point had the potential to cripple the Army of Northern Virginia and possibly destroy it entirely, giving the Union a real shot at victory by Christmas — but no one sent new forces to carry the attack forward. Union forces in the area withdrew from the Sunken Road. 5,500 men had been killed and wounded.

Shortly after the fighting for the Sunken Road began, Maj. Gen. Ambrose Burnside began his attack on one of the most famous portions of the battle. He was tasked with crossing Antietam Creek and attacking the Confederate right, but the Confederates were using the geography and the creek itself to make him pay dearly for every inch.

Only 500 defenders held the heights and the bridge. The heights were a huge advantage, placing the defenders approximately 100 feet higher than the attackers. Burnside's IX Corps attempted a two-pronged attack for three hours, suffering withering fire from the high ground before it was able to capture the bridge.

President Abraham Lincoln, when he learned of how the battle played out, lamented the fact that McClellan had failed to give chase to Lee, allowing Lee to get away with most of his army.

(Library of Congress)

According to an NPR article on the battle, the men from New York and Pennsylvania who finally took the bridge only did so after their commander promised to return their whiskey ration, taken after drunken antics had gotten the men in trouble.

But the Union had taken too long to capture the bridge. By that time, Confederate Gen. A. P. Hill was arriving with his men and they were able to pour into the Confederate right flank, shoring it up and repelling IX Corps before counterattacking.

When night finally fell, the two forces had suffered approximately 23,000 casualties with an estimated 4,000 killed, the worst loss of American life in a single day in history. To put that in perspective, approximately 2,500 Americans were killed taking Utah and Omaha beaches on D-Day.