During World War II, the U.S. Army Air Corps heavy bomber fleets of B-17’s, B-24’s, and B-29’s were examples of some of the most advanced technology of the period. These four-engine aircraft were designed and built to deliver tons of bombs to a target, defend themselves against enemy fighter attacks, and get their 10- or 11-man crews back to base, if possible. According to a postwar study of bombardier training, the first bombardiers in the Air Corps were pilots interested in bombing or enlisted personnel who had shown some interest and skill in bombing. Eighteen men graduated from the first class of bombardier training in February 1941. By September 1945, 47,000 bombardiers had been trained by the Army Air Force Training Command.