William was born in Pennsylvania to two immigrants from England and Scotland in 1846, although some sites show his birth being in 1845. He enlisted in the 29th Pennsylvania Volunteers on the 15th of August 1864, and during the American Civil War, he participated in General Sherman’s March to the Sea. After the war, William remained in the Army but transferred to the 23rd US Infantry in New York, with whom he deployed to the Arizona Territory in support of the Indian Wars. It was his actions on the 27th of March 1873, at the rank of First Sergeant, that would later earn him the Medal of Honor. The citation reads:

Gallantry in action.

The amount of detail in that official citation must have you not needing any more context but in case you are selfishly wanting more, I can help. Captain George Randall led a group of soldiers, which included William, and Apache Scouts to Turret Peak during the night to launch a surprise attack at dawn. The group crawled on hands and knees through the night as to not make any noise and what is now known as the Battle of Turret Peak ended with the death of between twenty-six and fifty-seven natives, with more wounded and captured.

Two years after the battle, on the 12th of April 1875, William received the Medal of Honor and he went on to receive a commission to Second Lieutenant in the 12th US Infantry, reaching the rank of First Lieutenant by December of 1880. Two years later, William Allen, died of inflammation of the bowel on the 8th of January 1882. Since his birth date isn’t known, he was about 36 years old and he was originally buried at the Post Cemetery at Fort Mojave, Arizona Territory: Section 6, plot 12. His current gravestone lists his death as 1892 and he now rests in the San Francisco National Cemetery: Section OS, Row 48, Site 2.