The Mustang P-51 was a single-seat fighter used during World War II. Designed and built in record time by North Americans to British specifications, and for British use, it was fast and highly manoeuvrable at low altitude, well suited for tactical reconnaissance and ground attack. Rolls-Roycer Merlin engines, US-built by Packard, were fitted from 1942 onwards, providing better power for the high altitude combat fighter role. The P-51D variant was an unqualified success, and taken up in great number by the RAF and the USAAF.