North American P-51 variants

Over twenty variants of the North American P-51 Mustang fighter were produced from 1940, when it first flew, to after the Second World War, some of which were employed also in the Korean War and in several other conflicts. Numerous examples of the aircraft survive to this day, often as heavily modified air racers.

The prototype of the Mustang, designated NA-73X, was rolled out by North American Aviation on 9 September 1940, albeit without an engine, and was first flown the following 26 October. The Mustang was originally designed to use a low-altitude rated Allison V-1710 engine. Unlike later models, Allison-powered Mustangs were characterized by the carburetor air intake placed on the dorsal surface of the nose, immediately behind the propeller.

The first production contract was awarded by the British for 320 NA-73 fighters, named Mustang Mk I by an anonymous member of the British Purchasing Commission; a second British contract soon followed, which called for 300 more (NA-83) Mustang Mk I fighters. Contractual arrangements were also made for two aircraft from the first order to be delivered to the USAAC for evaluation; these two airframes, 41-038 and 41-039 respectively, were designated XP-51. The first RAF Mustang Mk Is were delivered to 26 Squadron at RAF Gatwick in February 1942 and made their combat debut on 10 May 1942. With their long range and excellent low-altitude performance, they were employed effectively for tactical reconnaissance and ground-attack duties over the English Channel, but were thought to be of limited value as fighters due to their poor performance above 15,000 ft (4,600 m).

RAF Mustangs (Mk Is, which were not drop tank capable) made history on October 22, 1942 when they escorted 22 Wellington bombers on a daylight raid to Germany, thus becoming the first RAF single-seat fighters to fly over the country during World War II.

The first American order for 150 P-51s, designated NA-91 by North American, were placed by the Army on 7 July 1940. This was on behalf of the RAF in a Lend Lease deal. All but the last 57 went to the British. After the attack on Pearl Harbor, the USAAF 'held back' these Mustang Mk IAs for their own use. 55 of these so-called P-51-1s were outfitted with a pair of K.24 cameras in the rear fuselage for tactical low-level reconnaissance and re-designated F-6A (the "F" for photographic, although confusingly also still referred to as the P-51 or P-51-1.) Two kept their P-51-1 designation and were used for testing by the USAAF.

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