The "Kotobuki" air-cooled aircraft engine was improved and developed into the "Hikari (light)" engine with the bore and stroke expanded to the limit of the cylinder (160 × 180 mm for a displacement of 32.6 L), with the power was increased to 720 PS. The "Hikari" was used in Type 95 carrier fighters and Type 96 Carrier Attack Plane.
Nakajima knew that engines of higher power would be needed and began work on a new two-row, 14 cylinder design that was based on the 160 × 180 mm cylinder design of the Hikari. The Ha-5 prototype engine was completed in 1933, producing 1,000 PS, combining features of the Bristol Jupiter and Pratt & Whitney R-1340 Wasp designs. The Ha-5 had separate camshafts for the front and rear rows of cylinders like American designs, rather than using a single, front-mounted camshaft and long pushrods to operate both rows of cylinder valves. An improved Ha-5 was developed as a 1,500 PS engine. In all about 5,500 Ha-5 engines were produced for the military.
Later on, as the weights of aircraft rose and higher speeds were required, Nakajima continued to improve the Ha-5 design, creating the "Ha-41" and "Ha 109", which shared the same 146mm x 160mm bore and stroke as the Ha-5, but were increased from the 950 hp of the Ha-5 to 1,260 hp and 1,440 hp, respectively. The unified code for the Ha-41 was "Ha-34". Later the engine was developed into an 18 cylinder, twin-row engine called the "Ha-219", but this never got past the development phase. All these engines used essentially the same cylinder heads, the differences being in supercharging and engine revolutions per minute. The Ha-5 and Ha-41 shared the same weight of 630 kg, while the Ha-109 weighed 720 kg due to its larger, twin-stage supercharger system. The Ha-41 was the primary engine of early variants of the Nakajima Ki-49 "Helen" bomber, and the Nakajima Ki-44 "Tojo" fighter, later versions of both planes using the more powerful Ha-109 engine. Early versions of the Mitsubishi Ki-21 "Sally" used the Ha-5. The Ha-41 would have been an ideal powerplant in aircraft that used the Mitsubishi Kasei, being of smaller dimensions and displacement, yet making equivalent power levels.
About 7,000 civilian and 5,500 military Ha-5's were built during World War II.
The Ha-41 engine was used to power:
The Ha-109 engine was used to power: