Cub Driver wrote:

The Nakajima Ki-43 Hayabusa 'oscar' was very similar in shape, and also used
the same engines

In fairness to the army plane, the Hayabusa came first. The army
turned it down because of its perceived weaknesses in dogfighting.

Then the Zero was having trouble meeting specifications. So Mitsubishi
ditched its engine and borrowed the one Nakajima had developed for the
Hayabusa, and which of course was available since the Ki-43 wasn't
going into production.

Dan, I recall reading an account by IIRR Horikoshi, who said that it was strongly
implied to them by the navy that they should use the Nakajima engine, if they
wanted to see the a/c put in production. Mitsubishi was planning to use their
own (slightly less powerful, but IIRR lighter) engine in the a/c, but the
Japanese had a military-industrial-political complex too. It didn't have
anything to do with a lack of performance according to him. I'll try and find
the book and refresh my memory.

Guy