The 393d Bombardment Group is an inactive United States Air Force unit. It was last assigned to the Second Air Force, being stationed at Sioux City Army Air Base, Iowa. It was inactivated on 1 April 1944. Activated during World War II as a B-17 Flying Fortress operational training unit (OTU). Redesignated as a replacement training unit (RTU) in August 1943. Inactivated in April 1944 when Second Air Force switched to B-29 Superfortress training.