In spite of the degradation in performance, the USAAC was generally pleased with the Airacobra, and an initial order for 80 production examples (Bell Model 13) was issued on August 10, 1939 under Contract AC13383. Serials were 40-2971/3050.
For some reason, the USAAC allocated the new designation of P-45 to these machines, even though they were almost identical to the YP-39 service test aircraft. However, in the political climate of 1940, it was virtually impossible for the USAAC to acquire any new aircraft. But it could order more examples of an already-existing model. Consequently, the designation of the Airacobra was changed to P-39C prior to the delivery of the first aircraft.
The first P-39C (Ser No 40-2971) flew in January of 1941. The P-39C was almost identical to the YP-39, with the exception of the engine, which was a 1150 hp Allison V-1710-35 (E4). The production of the P-39C began in 1940.
The Army discovered almost immediately that the P-39C was not combat ready, since it lacked armor and self-sealing tanks. In the event, only twenty Airacobras were actually completed to C-standards--serial numbers 40-2971/2990. On September 14, 1940 the initial order for 80 P-39Cs was amended to provide for self-sealing fuel tanks. The remaining 60 planes of the order ( serial numbers 40-2991/3050) were completed to this standard and were redesignated as P-39Ds.
The P-39C was powered by a 1150 hp Allison V-1710-35 engine. Weights were 5070 pounds empty, 7075 pounds gross (combat weight), and 7300 pounds maximum takeoff. Maximum speed was 379 mph at 13,000 feet. An altitude of 12,000 feet could be reached in 3.9 minutes. Service ceiling was 33,200 feet. Armament was one 37-mm cannon, two 0.50-inch and two 0.30-inch machine guns, all in the nose.