At age 15, he earned the United States military's highest decoration, the Medal of Honor, for his actions at the Battle of Antietam.

Cook enlisted in the Union Army at age 14[1] in Cincinnati, Ohio, and served as a bugler in Battery B of the 4th U.S.

[2] During the Battle of Antietam on September 17, 1862,[2] his unit supported General John Gibbon's attack down the Hagerstown Turnpike.

Cook helped a wounded officer to the rear and, upon returning to his unit, found that most of the cannoneers had been killed.

He continued to work as a cannoneer throughout the attack, despite intense fire from Confederate soldiers who came within 15 feet of the guns.