The CurtissP-40 Warhawk was a single-seat fighter and ground attack aircraft developed by the United States in 1938. It began as a modified version of the P-36 Hawk, an aircraft that Curtiss had previously built. It was equipped with a single engine (normally an Allison V-1710 V-12), two .50 in (12.7 mm) machine guns in the nose, and two .303 Browning machine guns on each wing. Later versions, however, would have three .50 in (12.7 mm) guns in each wing. The P-40 was produced until November 1944, and was used in the air forces of 28 nations, including Great Britian.