The P-51 Mustang, designed in 1940 after Great Britain requested that North American build P-40 Warhawks for the Royal Air Force, was at first ignored by U. S. officials.  However, the design showed such promise that in 1941 the Army Air Forces took delivery of P-51A's powered by the Allison V-1710 engine.   These early Mustangs were restricted to reconnaissance and ground attack due to the limited performance of the Allison engines.  Tests in 1942 with the Roll-Royce "Merlin" engine showed a marked increase in performance.  By the end of 1943, Merlin powered P-51Bs entered  combat with the 354th Fighter Group in England.   Eighth Air Force Mustangs provided long range escort to B-17s and B-24s and scored heavily over German interceptors. By the war's end, P-51s had destroyed 4,950 enemy aircraft in the air, more than any other U. S. fighter in Europe.

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Mustangs served in nearly every active combat zone, including the Pacific where they escorted B-29s from Iwo Jima to Japan. Between 1941 and 1945, the Army Air Force ordered 14,855 Mustangs (including A-36A dive bomber and F-6 photo-reconnaissance versions), of which 7,956 were P-51Ds with the "bubble" canopy and heavier armament.  During the Korean Conflict, P-51Ds were used primarily for close support of ground forces until withdrawn from combat in 1953.  P-51s served with Reserve and National Guard units until 1957.