The Boeing B-17 Flying Fortress is perhaps the most renowned four-engine heavy bomber aircraft of the 2nd World War. In 1934 the United States Army Air Corps tendered a proposal to replace the old Martin B-10, which had now become outdated. The B-17 first saw combat with the British Royal Air Force.during the second World War. The RAF, in fact, entered into war with a limited number of heavy bombers, equipping its units with the first B-17Cs obtained from the United States, which were renamed B-17 Mk.I. The first operational missions against strategic targets in Germany, such as the industrial city of Wilhemshaven or the busy port of Brest, began in July 1941. The B-17 Mk.I possessed 4 powerful Wright R-1820-65 turbo-charged radial engines and was capable of carrying a large bombload, even on longer-range missions. From an industrial point of view, the B-17 is considered to be the first large aircraft to be produced on a large scale, utilizing the most advanced mass production techniques.