The engine had yet to find an application and bombing had destroyed the factory where production was to take place.
In response, in December 1942, the Army issued a request for a new radial aircraft engine capable of more than 2,500 hp (1,900 kW) which was to be designated Ha.51.
[1] The resulting Hitachi design was one of the first radial aircraft engines with more than twenty cylinders developed anywhere in the world.
[2] The engine had a steel crankcase, with an aluminium head mounted on steel cylinders each of bore 130 mm (5.1 in) and stroke 150 mm (5.9 in), similar to the eighteen-cylinder Nakajima Homare, but angled at 60° rather than 78° to accommodate the additional four cylinders.
[6] The engine reported very high oil consumption, up to 20g/kW⋅h, which was attributed to the rigidity of the crankcase.