The Kawasaki Ki-100 was a successful fighter aircraft produced by fitting a radial engine into the airframe of the Ki-61 Hien, after American bombing destroyed the factory producing the inline engine used in the older fighter.
In an attempt to improve the performance of the Ki-61 Kawasaki had produced a new version powered by their own Ha-140 engine, a modified version of the Ha-40, which was itself a licence-built version of the Daimler-Benz DB 601. The new engine had a great deal of potential, and when it worked properly the Ki-61-II was a potent fighter, but the Ha-140 was an unreliable engine. Even so full production of the -II got underway, and by mid-January 1945 Kawasaki had produced 374 airframes and 99 completed aircraft. On 19 January 1945 disaster struck when B-29 bombers from the US 20th Air Force destroyed the Akashi engine factory, where the Ha-140 was being produced. This left Kawasaki with 275 complete airframes with no engines, and the Japanese Army Air Force in desperate need of a fighter capable of reaching the high flying B-29s.
Two months before the destruction of the Akashi factory work had begun on finding an alternative engine that could be used in fighters. With not suitable inline engine available in any numbers, the search turned to radial engines, and in particular the Mitsubishi Ha-112-II twin-row 14-cylinder air cooled radial engine. This produced the same power as the Ha-140, and was lighter than the more complex inline area, but it had a diameter of 4ft, making it significantly wider than the 2ft 9in wide fuselage of the Ki-61.
Kawasaki solved the problem very quickly. The Ha-112 was smoothly faired into the top and bottom of the airframe, while at the sides the engine cowling remained wider than the fuselage, giving the aircraft a bulging nose when seen from above.
The Ki-100 prototype, produced by fitting the new engine to a Ki-61-II KAI made its maiden flight on 1 February 1945, only two weeks after the destruction of the Akashi factory. The lighter engine helped improve the aircraft's handling, while the top speed was only reduced by 13mph. The Ki-100 was easier to fly than the Ki-61-II, and much more reliable.
Production and Variants
Three of the existing Ki-61 airframes were used to produce prototypes for the Ki-100.
The remaining 272 Ki-61 airframes were used to produce the Ki-100-Ia, with the same guns as the Ki-61-II KAIa, two 20mm cannon in the fuselage and two 12.7mm machine guns in the wings.
Once the existing airframes had all been converted production of new Ki-100s began. This version had a modified fuselage, with a cut-down rear fuselage and a bubble cockpit that improved the pilot's view. A total of 118 Ki-100Ibs were produced, most at the Kagamigahara factory, although 12 were completed at Ichinomiya before American bombing ended production there.
Three prototypes were produced of the Ki-100-II, powered by the Ha-112-IIRU radial engine with a Ru-102 turbo supercharger. The war ended before this version could enter production.
The Ki-100 was seen by many of its pilots as the best Japanese fighter of the war. It had a much better rate of climb than the Ki-61-II and was much more manoeuvrable at high altitude. It entered service with conversion units in March 1945, and in April the 5th, 59th, 200th and 244th Sendais received the type. By the end of July the 17th, 18th, 25th, 111th and 112th Sendais had also received the Ki-100.
The Ki-100 was easy to handle, making it suitable for the large number of newly trained but inexperienced pilots being produced in Japan in the last few months of the war. Even so these new pilots were shot down in large numbers, often without achieving anything. As an example of the large numbers of aircraft lost, the 111th Regiment was given around 150 Ki-100s in the short period it operated the aircraft. Given that its normal complement of aircraft was only 57, nearly 100 fighters were lost in a short time.
In more experienced hands the Ki-100 could be a very dangerous opponent, and the few surviving Japanese 'aces' performed well in their new mounts. The Ki-100 could outperform the F6F Hellcat, and hold its own against the P-51 Mustang, and a number of the better Japanese pilots achieved an impressive number of victories in the final air battles over Japan.
Engine: Mitsubishi Ha-112-II radial engine
Wing span: 39ft 4.5in
Length: 28ft 10.5in
Height: 12ft 3.5in
Empty Weight: 5,952lb
Maximum Weight: 8,091lb
Max Speed: 367mph at 32,810ft
Service Ceiling: 35,005ft
Range: 1,243 miles
Armament: Two fuselage mounted 12.7mm Ho-103 Type 1 machine guns, two wing mounted 20mm Ho-5 cannon
Bomb-load: Two drop tanks or two 551lb bombs