During the height of World War 2 (1939-1945), all major participants undertook various programs to further evolve existing weapons platforms. For the Japanese concern of Kawasaki, a 1943 initiative produced the experimental "Ki-64" single-seat, piston-driven fighter. The type managed to be constructed through only a single prototype offering and the program, as a whole, was abandoned shortly after a test flight ended in a forced landing due to fire. First flight of the Ki-64 was recorded sometime in December of 1943 and the aircraft was codenamed "Rob" by the Allies.
For all intents and purposes, the Ki-64 was of a conventional fighter aircraft design with a unique internal arrangement intended to promote excellent top-line speeds and performance essential to countering developments by the Americans in the Pacific. One of the most notable qualities of the design was its coupling of two Kawasaki Ha-40 Army Type 2 liquid-cooled, inline piston engines which, when mated, was recognized under the designation of "Ha-201". It is noteworthy that the Ha-40 was nothing more than a localized production copy of the excellent German-originated Daimler-Benz DB 601Aa series inline engine powering the equally-excellent Messerschmitt Bf 109 fighter - manufacturing licenses granted to both Kawasaki and Aichi Japanese concerns. The powerplant provided the Kawasaki airframe with an output of some 2,350 horsepower allowing for top speeds of nearly 430 miles per hour and an operating ceiling near 40,000 feet. Range was out to 620 miles with a rate-of-climb of approximately 3,000 feet per minute. The airframe exhibited an empty weight of 9,000lbs and a gross weight of 11,200lbs. Kawasaki classified their Ki-64 as a "heavy" fighter as a result. The Ha-40 was later redesignated to "Ha-60" following the 1944 restructured designation system.
Outwardly, the Ki-64 showcased a basic fighter form including straight, low-mounted wing apendages, a streamlined airframe and single, curved vertical tail fin. The undercarriage was wholly retractable of the "tail dragger" variety. The pilot sat ahead of amidships under a lightly-framed canopy with adequate views of the action. Due to the limited internal volume of the airframe (of slim design profile), one of the Ha-40 engines was fitted ahead of the cockpit in the usual way with the second engine added to a compartment just aft of the cockpit. The rear engine was connected to the forward system via a drive shaft running under the cockpit floor (similar to the American Bell P-39 Airacobra fighter). This allowed full output from both engines to be featured or the ability to fly on a single unit if need be. To the engine pairing was added 2 x three-bladed propeller systems arranged in a contra-rotating fashion, designed to take full advantage of performance output at speed. It is noteworthy that engine output was not combined to both propellers. Instead, the rear engine drove the frontal propeller assembly independently of the front engine driving the rear-set propeller. The forward propeller was of a variable pitch design while the rearward propeller was fixed pitch.
As a fighter intended to tackle enemy fighters in turn as well as Allied bombers pummeling Japanese territorial and mainland installations, Kawasaki considered their Ki-64 with a battery of 4 x 20mm Ho-5 series cannons or 2 x 20mm Ho-5 cannons supplemented by 2 x 12.7mm Ho-103 series heavy machine guns. In either case, this armament array would have been formidable in combat.
Testing of the Ki-64 continued into 1944. During its fifth flight, the rear engine installation erupted into fire which immediately sent the pilot into landing the aircraft. While the landing proved successful without loss of life, the impact of the crash damaged the test frame considerably. This proved an insurmountable setback for the program to which the Ki-64 was dropped from further development, leaving it to the pages of military aviation history.
Like many other programs begun prior to the end of the war in 1945 (be they aircraft or tank), the Ki-64 airframe was eventually captured and overtaken by the advancing Allies. Its design was then handed over to American engineers for study before being discarded to the scrapheap. Thus ended the short-lived reign of the Ki-64 heavy fighter.