Boeing YB-40 Flying Fortress Boeing YB-40 Flying Fortress The Boeing YB-40 Flying Fortress was a modification for operational testing purposes of the B-17 Flying Fortress bomber aircraft, converted to act as a heavily armed gunship for other bombers during World War II. At the time of its development, long-range fighter aircraft such as the North American P-51 Mustang were just entering quantity production, and thus were not yet available to accompany bombers all the way from England to Germany and back. Work on the prototype, Project V-139, began in September 1942 by converting the second production B-17F-1-BO (serial number 41-24341) built. Conversion work was
76th Flying Training Wing (World War II) from single and two-engine aircraft to the B-17 or B-24 Liberator heavy bombers. Also after 1944, most pilots were learning on B-17/B-24s for eventual transition to B-29 Superfortress training under Second Air Force. As training requirements changed during the war, schools were activated and inactivated or transferred to meet those requirements. The schools of the wing flew primarily B-17D/E/F Flying Fortresses. Some B-17Gs were flown after June 1944 when Second Air Force B-17 training ended. Some B-24D Liberators were also used 76th Flying Training Wing (World War II) The 76th Flying Training Wing was a wing of the United States