Pilot Training Manual for the B-17 Flying Fortress - Paperbackby United States Army Air Force (Author), C. a. Brown (Editor) With the first prototype rolling off the assembly line in 1935, the Boeing B 17 Flying Fortress was the world's first truly mass produced four engined heavy bomber. The B 17 was used as the backbone of the US Army Air Force's strategic bomber forces through all theaters of the Second World War. Used as a strategic bomber from Europe to Burma to the Pacific and North Africa, the B 17 earned