B-17 Flying Fortress units of the United States Army Air Forces 2d Bombardment Group, Langley Field, Virginia on 11 January 1936; the first production B-17B was delivered on 29 March 1939 also to the 2nd Bombardment Group. A total of 12,677 production Fortresses was built before production came to an end. In August 1944, the Boeing B-17 equipped no less than 33 overseas combat groups. The last Boeing-built B-17G was delivered to the USAAF on 13 April 1945. Following the end of World War II, the Flying Fortress was rapidly withdrawn from USAAF service, being replaced by the B-29 Superfortress. Literally thousands of Fortresses used in combat in Europe by Eighth
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