During the Korean War, Sergeant First Class Mumford was a member of the 7th Cavalry Regiment, 1st Cavalry Division. He was wounded by the enemy on 5 October 1951 and returned to duty on 9 January 1952. In 1953, he was assigned as a training cadre at Ft. Dix, New Jersey. He died of other causes on 17 September 1953.

Mumford was awarded the Purple Heart, the Combat Infantryman's Badge, the Korean Service Medal, the United Nations Service Medal, the National Defense Service Medal and the Korean War Service Medal.