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-I entered service. The Ki-61-I-Ko was equipped with two wing-mounted 7.7 mm machine guns and two fuselage-mounted synchronous 12.7 mm machine guns. The Ki-61-I-Otsu’s four machine guns were all large-caliber.
All in all, 1380 Ki-61-I-Ko and Ki-61-I-Otsu aircraft were manufactured, including prototypes.