Mitsubishi and partners Nissan and Fuji proceeded with development of the airframe and Yokosuka Arsenal was adapting the engine for Japanese production, designated the Ro.2. The Japanese succeeded in producing prototypes that outwardly looked very much similar to the "Komet". The J8M1 had a wet weight that was lighter, the aircraft having a plywood main spar and wooden vertical tail. The designers had also dispensed with the armoured glass in the cockpit and the aircraft carried less ammunition and slightly less fuel.