The Kawasaki Ki-100 was a one of the best Imperial Japanese WW2 fighter aircraft. It was a powered with Mitsubishi Ha 112-II radial engine (1,120 kW (1,500 hp) at take off).
The Kawasaki Ki-61-II with the company’s Ha-140 engine was seen as an interim high-altitude interceptor to tackle the USAF’s Boeing B-29s at their cruising altitude of some 9144m (30,000ft). However, development of the Ha-140 as a reliable powerplant was terminated finally when the Akashi factory where the engine was built was destroyed during an air raid. With the requirement becoming daily more urgent, Kawasaki was instructed to convert the 275 Ki-61-II airframes gathering dust in the Kagamigahara factory with alternative powerplant.
No other similar engine was available and adaptation of the slender fuselage of the Ki-61 to allow installation of a large-diameter radial engine at first appeared impractical. However, Kawasaki’s design team converted three airframes to serve as prototypes, installing a Mitsubishi Ha-112-11 engine which had the same power output as the unreliable Ha-140. When the first of these was flown, on 1 February 1945, Kawasaki discovered that it had a firstclass fighter, one that some commentators have described as Japan’s premier fighter aircraft of the Pacific war.
By the end of May 1945 all of the remaining 272 Ki-61 airframes had been converted to the new configuration, entering service as the Army Type 5 Fighter Model 1A, which was identified by the company as the Kawasaki Ki-100-Ia.
With the Ki-100 proving such a success, it was decided to initiate production of this aircraft, the resulting Ki-100lb differing only by having the cutdown rear fuselage and all-round-view canopy that had been designed for the proposed Ki-61-III. A total of 99 of this version was built before production was brought to an end by the growing weight of USAAF air attacks, A more effective version had been planned, to be powered by the Mitsubishi Ha-112- Ilru engine which incorporated a turbocharger to improve high-altitude performance, but only three of these Ki-100-11 prototypes had been built and flown by the end of the war.
The Kawasaki Ki-100 made its combat debut on the night of 9 March 1945, and suffered its first loss on 7 April 1945, when a Ki-100 flown by Master Sergeant Yasuo Hiema of the 18th Sentai was shot down by a B-29.
During March and April 1945 experienced instructors from the Akeno Army Flying School flew the Ki-100 in extensive tests against the Ki-84, which was considered to be the best of the JAAF fighters then in operational service. Their conclusions were that, given pilots of equal experience, the Ki-100 would always win in combat. An overall assessment of the effectiveness of the Ki-100 rated it highly in agility and a well-handled Ki-100 was able to out-manoeuvre any American fighter including the formidable P-51D Mustangs and the P-47N Thunderbolts which were escorting the B-29 raids over Japan by that time, and was comparable in speed especially at medium altitudes.