Nakajima provided Japan with its first large radials by building licensed Bristols beginning in the late 1920s, and Gnome-Rhone engines beginning in 1936. Nakajima built three 14-cylinder radial engines. The pre-World War II Mamoru possibly shares characteristics with the Pratt & Whitney R-2000. It was the most powerful 14-cylinder engine ever built, with versions at 1,790 kW (2,400 hp) and one of
Frank B. Halford was a talented independent British engine designer of the early and mid-twentieth century who worked for a number of manufacturers including de Havilland, Cirrus and Fiat. In 1928, he contracted with Napier for design of a series of air-cooled engines in a vertical H configuration having twin crankshafts geared together. There were two basic types, the 16-cylinder Rapier and the 2