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 the most experienced B-17 units, and their departure from England slowed down the development of the Eighth Air Force’s offensive. Later, two newly trained II Bomber Command groups (2d, 99th) deployed from the United States. The four B-17E groups formed the heavy bomber component of XII Bomber Command (and Northwest African Strategic Air Force). In North Africa Flying Fortresses were used against German and Italian military targets in Algeria and Tunisia, and to attack German shipping in the Mediterranean. Flying Fortresses took part in the bombardment of the Italian stronghold of Pantelleria, the invasion of Sicily and the invasion of