The Bell P-63 Kingcobra is an American fighter aircraft developed by Bell Aircraft during World War II. Based on the preceding Bell P-39 Airacobra, the P-63's design incorporated suggestions from P-39 pilots and was superior to its predecessor in virtually all respects. The P-63 was not accepted for combat use by the United States Army Air Forces. However, it was deployed during World War II by the Soviet Air Force,[2] which had also been the most prolific user of the P-39. In September 1942, even before the prototype flew, the USAAF ordered it into production as the P-63A (Model 33). The P-63A's armament was to be the same as the current P-39Q, a single 37 mm (1.46 in) M4 cannon firing through the propeller hub, two synchronized .50 caliber (12.7 mm) machine guns in the cowl, and two .50 cal (12.7 mm) machine guns in underwing gondolas.