When production of the Kestrel engine ceased, a new variant of the Master was designed that used an air-cooled Bristol Mercury XX radial engine, capable of producing 870 hp (650 kW), instead. Thus configured, on 30 October 1939, the first "M.19 Master II" prototype made its first flight; 1,748 aircraft were eventually built. After the Lend-Lease programme provided a supply of engines from the United States to Britain, a third variant of the Master, designated "M.27 Master III", was designed, which was powered by the American-built Pratt & Whitney Twin Wasp Junior, a two-row radial engine that could generate 825 hp (615 kW). A total of 602 Master IIIs were constructed.