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-17G "Flying Fortress" No. 44-83690 and in 1961, flown to Grissom Air Force Base (then known as Bunker Hill) for permanent display. The Heritage Museum Foundation, established in 1981 as part of the Air Force Museum Program, maintains 44-83690. In 2015 the aircraft was moved to the Museum of Aviation at Robins AFB, Georgia and is currently undergoing a lengthy restoration. B-17G "Flying Fortress" No. 44-83690 is a reasonably intact example of a World War II aircraft type of which only 50 exist in the world. It is also an example of an experimental craft, which participated, in military tests shortly after World War II.