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
B-17 Flying Fortress units of the United States Army Air Forces Liberators Was primary operator of B-17 Flying Fortresses in overseas combat theaters during World War II. The B-17 may have first seen combat in American markings in the Philippines, but it would earn its enduring fame with the Eighth Air Force, based in England and fighting over Occupied Europe. The story of the B-17 would become the story of the VIII Bomber Command (later Eighth Air Force) strategic heavy bombardment campaign of the European Theater of Operations (ETO) during World War II Initially equipped with B-17Es in 1942, the Eighth Air Force received B-17Fs in Jan 1943 and B-17Gs in