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| | Boeing B-17 Flying Fortress - USA |
 | | By September 1943, the Flying Fortress showed its final shape during firepower tests on the XB-40, a modified B-17F with the advantage of a "chin" turret. |
 | | The Flying Fortress was designed for a USAAC competition, announced in 1934, to find a modern replacement for the assorted Keystone biplane bombers, then in service. |
 | | Twenty B-17Cs were delivered to the RAF as Fortress Is, which quickly showed that defensive armament was inadequate, (the B-17C carried seven 50-cal. machine-guns) and at high altitude raids of 30,000 ft. (9,144 m), the defensive guns froze up, when they tried to fire them. |
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