Boeing B-17 Flying Fortress NAN10-50.jpg|thumb|B-17 modified for testing of the [[Pratt & Whitney T34|XT-34 turboprop]]. When testing concluded, the aircraft was restored to stock configuration as the "[[Liberty Belle (B-17)|Liberty Belle]]", but was lost in a post-forced-landing fire near [[Oswego, Illinois]] on 13 June 2011.]] [[Category:Boeing aircraft|B-17 Flying Fortress]] [[Category:United States bomber aircraft 1930–1939]] [[Category:Four-engined tractor aircraft]] [[Category:Low-wing aircraft]] [[Category:World War II bombers of the United States]] [[Category:Boeing B-17 Flying Fortress| ]] [[Category:Aircraft first flown in 1935]] Boeing B-17 Flying Fortress The Boeing B-17 Flying Fortress is a four-engined heavy bomber developed in the 1930s for the United States Army Air Corps (USAAC). Competing
RAF Bomber Command aircrew of World War II aircrew were given the task of flying a required number of operations, an "operational tour", usually of about 30 operations (missions in USAAF terminology). On completion of an operational tour the airman (and often his complete crew as they tended to remain very tight-knit, always flying together) would be "screened" (taken off operational flying) and split up as they received their future postings which would frequently be serving at Operational Training Units or Heavy Conversion Units preparing the next groups of young bomber crews for their postings to operational squadrons. Between March 1943 and the early summer of 1944 the