Henry Royce's last design was the Merlin aero engine, which was first flown in prototype form in 1935, although he had died in 1933. This was developed from the R engine, which had powered a record-breaking Supermarine S.6B seaplane to almost in the 1931 Schneider Trophy. The Merlin was a powerful supercharged V12 engine and was fitted into many World War II aircraft: the British Hawker Hurricane, Supermarine Spitfire, de Havilland Mosquito (twin-engine), Avro Lancaster (four-engine) (a development of the Avro Manchester with its unreliable Rolls-Royce Vulture engines), Vickers Wellington (twin-engine); it also transformed the American North American P-51 Mustang into a competitor for the best fighter of its time, its engine a Merlin engine built by Packard under licence. Over 160,000 Merlin engines were produced, including over 30,000 by the Ford Motor Company at Trafford Park, Manchester. During the war most Rolls-Royce flight testing of engines was carried out from Hucknall Aerodrome. The Merlin crossed over into military land-vehicle use as the Meteor powering the Centurion tank among others. Many Meteor engines used engine blocks and parts that failed requirements for high performance engines, but were suitable for use in the derated Meteor.