The Antietam Half Dollar, also known as the Lee-McClellan Half Dollar, is the only commemorative half dollar that was authorized, produced, sold, and imprinted with the same year, 1937. It commemorates the observation of the 75th anniversary of the Battle of Antietam, which took place 75 years earlier on September 17, 1862.

Designed by William Marks Simpson, the obverse shows portraits of McClellan and Lee in profile facing left. Their rank and names are below the truncation on two lines, the words separated by stars. Below, near the edge, is the denomination HALF DOLLAR. The inscription UNITED STATES OF AMERICA is in an arc at the top. Between it and the denomination, on the left is the motto IN GOD WE TRUST, and on the right is LIBERTY. Three stars are below LIBERTY. One star is before and one after the motto. The reverse shows the Burnside Bridge, which is named beneath it. Below the name is the date of the battle. Above the trees is the motto E PLURIBUS UNUM. In an arc near the edge of the coin is the inscription SEVENTY-FIFTH ANNIVERSARY BATTLE OF ANTIETAM and the date is below.

The battle was fought near Sharpsburg, Maryland and is also called the Battle of Sharpsburg. It was the bloodiest single day battle of the Civil War. Approximately 25,000 soldiers were killed. In the battle, Lee was opposed by his West Point student McClellan. Despite the fact that the outcome of the battle was inconclusive, stopping Lee from invading Maryland was enough of a victory for Lincoln to announce the Emancipation Proclamation. This announcement discouraged the French and British from their plans to recognize the Confederacy.

The original mintage of the coin was 50,028. However, 32,000 were returned to the Mint for melting, making the net number distributed 18,028. The Washington County Historical Society of Hagerstown, Maryland was the issuing agency. The coins were offered for sale at $1.75 each, with no limit on the number that could be ordered. Late in 1937 the Society changed the price to $1.65 per coin. Buyers were told that the limited distribution would have an effect on the value of the coin. However, the effort was a failure.
The original packaging of the coin consisted of a cardboard holder that had spaces for five coins. Its cover was imprinted with the manufacturer J.N. Spies Mfg. Co.

The Antietam Half Dollar was one of the three early commemorative issues that were made to specifically deal with a Civil War event. The others were the Stone Mountain and the Battle of Gettysburg half dollars.