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 B-17 Flying Fortress units of the United States Army Air Forces This is a list of United States Army Air Forces B-17 Flying Fortress units of the United States Army Air Forces including variants and other historical information. Heavy bomber training organizations primarily under II Bomber Command in the United States and non-combat units are not included. The B-17 Flying Fortress was perhaps the most well-known American heavy bomber of the Second World War (1939/41-1945), . It achieved a fame far beyond that of its more-numerous contemporary, the Consolidated B-24 Liberator. The first pre-production Y1B-17 Fortress was delivered to the