Kawasaki Ki.61 / Ki.100 Hien ("Tony")

Ki.61-Ia (30 kb)
One of the first Ki.61-Ia of major Teruhiko Kobayashi, seen here with 5 kill markings.

The Hien (meaning: "Swallow") was technically unique amongst Japanese WW2 fighter planes, because it used an inline engine instead of a radial. This family of engines was in fact of German origin, the Kawasaki Ha-40 inverted V12 being simply a license-built version of the Daimler-Benz DB-601A, which was powering the Messerchmitt Bf 109E.
Kawasaki was asked to build two planes with this engine: the Ki.60 heavy interceptor and the Ki.61 light, all-purpose fighter. However, after the first tests showed disappointing performance, the Ki.60 was cancelled.
The long cowling housing the inverted V12 gave the Ki.61 an European look, very similar to either a Bf 109E or an Italian fighter with a similar engine; this might explain its allied code name: Tony.

Development

Ki.61-I

Kawasaki Ki.61-I-KAIc Hien "Tony"
Engine Kawasaki Ha-40 inverted V12 1,100 hp (WEP: 1,180 hp)
Weight empty: 2,630 kg (5,798 lb) - maximum: 3,470 kg (7,650 lb)
Armament Two cowl-mounted 12.7mm guns, two wing-mounted Ho-5 20 mm cannons
Performance Max speed: 589 km/h (366 mph) Ceiling: 10,000 m (32,810 ft)
By the spring of 1944, production of the Ki.61-I had fallen to a low level because of shortages of the unreliable Ha-40 engines. Production was finally terminated in January of 1945.

Ki.61-II

Ki.61-III

Ki.100

Because of shortages and unreliability, the Ha-140 engine of the Ki.61-II could not be produced as fast as the airframes. On January 19, 1945, the destruction of the Kawasaki engine factory by a B-29 raid settled it: other engines had to be fitted. The marriage of the 275 engineless Ki.61-II airframes with the available (and reliable) 1,500 hp Mitsubishi Ha-112-II fourteen-cylinder double-row radial engine led against all odds to a very successful result: the excellent Kawasaki Ki.100.
The Japanese engineers studied a German-supplied FW 190A-4 to solve their main problem: how to efficiently fit a bulky radial engine to a thin airframe.

Ki.100 (31 kb)
The Ki.100 of Lt Mamoru Tatsuda, wingman of Major Hinoki.

The Ki.100 is undoubtly the best Japanese Army fighter of WW2; it was more than a match for the P-51 Mustang, but the low numbers of planes available could have no effect against the inevitable defeat.
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