The Daimler-Benz DB 601Aa was a development of the earlier
DB 600, with direct fuel injection replacing the carburetor. Like all DB 601s, it had a 33.9-litre displacement. The first prototype with the direct fuel injection was test run in 1935, and an order for 150 engines was placed in February 1937. A manufacturing license was granted to
Aichi for the production of this engine for the
Imperial Japanese Navy as the
Atsuta and to Kawasaki for production of this engine for the IJAAS as the Ha40. Under the 1944 Unified System, this engine was re-designated as the Kawasaki Ha-60. The Kawasaki Ha40 and the
Aichi Atsuta were based on the engine that powered Germany's
Messerschmitt Bf 109 fighter.
Ha201 A new high-horsepower narrow-profile engine was required for the
Kawasaki Ki-64 experimental fighter. The aircraft design called for a narrow-profile fuselage, and the solution that Kawasaki developed was the Ha-201 engine. Although similar to the
Aichi Ha-70, where two
Aichi Atsuta engines, mounted side-by-side behind the cockpit driving a single large propeller — an arrangement already used by the Daimler-Benz DB 606 that powered the
Heinkel He 119 reconnaissance monoplane prototypes, and later inspired Japan's own
Yokosuka R2Y reconnaissance aircraft from the seventh and eighth He 119 prototypes being sold to Japan in May 1940 — for the Japanese Ki-64, its own powerplant installation design called for the two Kawasaki Ha-40 engines to be separately mounted, one in the aircraft's nose, the other behind the cockpit. The engines were connected to a common gearbox that was mounted in the nose. The rear engine was connected to the nose-mounted gearbox by a long drive shaft similar to the American
Bell P-39 Airacobra. The gearbox did not combine the power output of the two engines. Instead, the rear engine drove the forward controllable-pitch propeller, while the front engine independently drove the rearward fixed-pitch propeller. ==Variants==