It was originally activated as the 20th Transport Squadron in 1940 and served as a troop carrier unit in Panama during and after World War II, until it was inactivated in 1949. Activated in 1965 as the 20th Tactical Air Support Squadron (TASS), it served notably for seven and a half years of combat duty during the Vietnam War, and was inactivated in 1973. While in inactive status, the two squadrons were consolidated into a single unit. The 20th TASS was reactivated at Shaw Air Force Base in 1990, and again inactivated on 31 December 1991.