The Kawasaki Ki-61 "Hien" (Swallow) was a Japanese World War II fighter powered by a V-12 engine.
The Ki-61 had many design similarities with the Heinkel He 100 and He 112. What is interesting is that the Japaneses have bought aircraft in Germany to test them in Japan. One of those German aircraft was the single seat Messerschmitt Bf 109. Chief design engineer was, Takao Doi, who was trained by the German engineer Richard Vogt, Doi´s precursor as the chief designer by Kawasaki.
The prototype of the Ki-61 had its first flight in December 1941. The first aircraft (Ki-61-I) entered operational status in summer 1942. Many other derivatives were developed with better armament, engines, armor and canopies.Not only the design was German, German weapons were also used, like the 20-mm-MG-151/20-Mauser-cannons, making the armament of the "Tony" (allied codename of the "Hien") very good. Indeed at the beginning it was euipped with 12.7 mm machine guns only; but a short time later up to four 20 mm guns were used. Some variants, for excampel the Ki-61-I-KAId were equipped with 30-mm machine guns.
The Ki-61 was also used as a fighter-bomber. It was able to carry 500 kg of payload (two 250 kg bombs).
But this agile fighter also had problems: Like on the He 100, the Ki-61 had trouble with the cooling system. And at the end of the Pacific War the quality of the produced aircraft was bad because of allied attacks on the factories in which many workers died.