The "Airacobra's" unique design placed the engine behind the pilot. It used an Allison V-1710-85 12 cylinder, liquid-cooled, in-line engine with a single-stage rated at 1,200 horsepower.

The lack of a supercharger left the Airacobra under-powered at higher altitudes, yet it was quite effective in ground attacks.

Nearly half of the 10,000 P-39's built were exported to the Soviet Union where the pilots were intrigued by its toughness and durability.