The British Purchasing Commission asked North American to build a licensed version of the Curtiss H87A (P-40E) in April 1940. The President of North American, J. H. "Dutch" Kindelberger, suggested that he could build a new plane around the Allison V-1710 engine. This design became the NA-73.
After the initial order for the planes was placed by the British, the United States took two of the aircraft, named the XP-51, and had them tested at Wright Field in August 1941.
The United States Army issued a requirement for a XA-32 that became the A-36A, in 1942. 500 of these were ordered.
In 1942 the Army diverted from Lend Lease 55 Mustang IAs and these became the P-51.
Dive Bombing Effectiveness
Many were skeptical of the A-36As ability to dive bomb accurately with a dive speed of 390 mph.
Initially the A-36s were nicknamed the Apache and then the Invader, but reporters always called them Mustangs.