A lightweight multipurpose fighter plane, the Ki-61 Hien (“Swallow”) was well-armed and well-armored.
From the very beginning, the makers of the Ki-61 concerned themselves with protecting the fuel tanks and the pilot. The light multipurpose fighter was an effective answer to “hit-and-run” fighters, thanks to its survivability and high diving speed.
The Ki-61 had a Kawasaki Ha-40 liquid-cooled inverted V12 engine, a licensed copy of the DB 601A, capable of 1175 hp.
A prototype was ready in 1941, and by the next year the first production models were manufactured and the Ki-61 entered service.
In 1944, a modification designated as the Ki-61-Kai-Hei appeared, in which the nose guns were replaced by 20 mm cannons. Improved wing construction allowed the carrying of bombs and increased dive speed. In addition, the fuselage was lengthened, and the tail wheel was made non-retractable. 388 Ki-61-Ko and Ki-61-Otsu aircraft were upgraded to the Ki-61-Kai-Hei design.
All in all, 3,078 Ki-61 fighters (of various types) were produced.