Clopton specialized as a rifleman and served as Sergeant in the U.S. Marine Corps for four years. He enlisted on June 10, 1963, in Birmingham, Alabama. He received his military education at Tactics of the Marine Rifle Squad. In 1966, he served with the 26th Marines, 3rd Division. In 1967, he transferred to the 9th Marines to reinforce the unit known as the “Walking Dead”. He was described as an “excellent squad leader” in Keith Nolan’s book Operation Buffalo, USMC Fight for the DMZ.