The Ha-43 was Mitsubishi's answer to
Nakajima's
Ha-45. The engine was planned to produce while retaining high reliability and a superior
power-to-weight ratio compared to contemporary engines in its class. The frontal area per hp. was also intended to be the smallest in the world. However, such ambitious targets necessitated extraordinary efforts and ingenuity at the same time. At the time, Mitsubishi was working to promote a different engine, the Ha-42 (an 18-cylinder derivative of the
Kasei), development of which was prioritized above the Ha-43's, delaying its completion. Consequently, the Ha-45 entered service first, albeit plagued with reliability issues, which would also trouble the Ha-43. Numerous promising aircraft, such as the
Kyushu J7W interceptor and Mitsubishi's own
A7M Reppu fighter, were planned to use the Ha-43, but in the end, such aircraft did not see service before
Japan's surrender, nor did the engine itself. ==Variants and designations==