Technical Sergeant Duncan was a member of Headquarters and Service Company, 1st Marines, 1st Marine Division. He was taken Prisoner of War while fighting the enemy in Korea on 10 December 1950 and died in a prison camp on 15 June 1951. His remains were not recovered. His name is inscribed on the Courts of the Missing at the Honolulu Memorial.

Duncan was awarded the Purple Heart with Gold Star, the Combat Action Ribbon, the Korean Service Medal, the United Nations Service Medal, the National Defense Service Medal, the Korean Presidential Unit Citation and the Republic of Korea War Service Medal.