Master Sergeant Donald W. "Don" Duncan (born 1930) was a U.S. Army Special Forces soldier who served during the Vietnam War, helping to establish the guerrilla infiltration force Project DELTA there. Following his return to the United States, Duncan became outspoken in his opposition to the conflict and became one of a leading public figure in opposition to the war. Duncan is best remembered as the military editor of the radical monthly magazine, Ramparts, during the Vietnam conflict and for his testimony to the 1967 Russell Tribunal detailing American war crimes in Vietnam.