A British North American NA-73 Mustang Mk I (s/n AL958) being test-flown at Inglewood, California (USA) in October 1942. This plane was one of the original batch of 300 aircraft ordered by the Royal Air Force in December 1940 before the lend-lease act. Note that the fighter wears U.S. national insignias that were used by U.S. forces up to April 1942. Original caption: "North American's P-51 Mustang Fighter is in service with Britain's Royal Air Force, N [orth]A [merican]Aviation, Inc., Inglewood, Calif."