During the mid-1930s, the Japanese had an interest in powerful, low frontal area engines. Around 1940, the Japanese Navy began development of the YE3A, a 24-cylinder, liquid-cooled, X-type engine, derived from the 18-cylinder YE2A, having the same bore and stroke as the YE2H. By 1943, an experimental engine, known as Ken No. 1 (believed to be this YE3B, or Ha74 Model 01), was being developed and tested by the Yokosuka Naval Air Arsenal for internal wing installation. A similar engine for internal fuselage installation, known as Ken No. 2 (believed to be the YE3E, also Ha 74 Model 11), was rated at 2,386 kW (3,200 shp) and scheduled for completion in 1944.

However, none of the several high power liquid-cooled engines under development by Japan could keep up with the faster development of air-cooled radial engines, and did not reach operational status by the war’s end. Also the focus of international engine development had turned toward turbine engines.