North
American P-51D Mustangs
The North American P-51 Mustang was initially produced in response to a 1940 RAF requirement for a fast, heavily armed fighter able to operate effectively at altitudes in excess of 6100m (20,000ft). North American built the prototype in 117 days, and the aircraft, designated NA-73X, flew on 26th October 1940. The first of 320 production Mustang Is for the RAF flew on 1st May 1941, powered by an 1100hp Allison V1710-39 engine. The USAAF, somewhat belatedly [not unusual?], realized the fighter’s potential and evaluated two early production Mustang Is under the designation P-51. The first two USAAF Mustang variants, both optimized for ground attack and designated A-36A and P-51A, were fitted with Allison engines. Trials with Mustangs fitted with Packard built Rolls-Royce Merlin 61 engines showed a dramatic improvement in performance, maximum speed being raised from 627km/h (390mph) to 710km/h (441mph), and production of the Merlin-powered P-51B got under way in the autumn of 1942.
North American P-51D Mustang
The RAF, which had ordered 1000 P-51Bs under the designation Mustang Mk III, began to receive its first aircraft early in 1944, the first 36 aircraft having been diverted to the US Eighth AAF to alleviate the critical shortage of escort fighters. Complaints about the poor visibility from the Mustang’s cockpit led North American to test two P-51Bs with a one-piece sliding canopy and cut-down rear fuselage. Whereas the P-51B/C had been armed with four 12.7mm (0.50in) machine guns with l260rpg, the conversions, designated XP-51D-NA, had six 0.50 calibre Browning air-cooled machine guns with 1880 rounds in a strengthened wing. The aircraft were also later fitted with a dorsal fin to compensate for the loss of keel surface after the removal of the upper rear fuselage.
North American P-51D Mustang
Other refinements in the course of production included the addition of two sets of stub rocket launchers under each wing to carry 12.7cm (5in) rockets. The first production P-5lDs began to arrive in England in the late spring of 1944 and quickly became the standard equipment of the USAAF Eighth Fighter Command.
