The Kawasaki Ki-61 Hien (flying swallow) was designed to use the
licensed copy of the German Daimler-Benz 601 engine, manufactured in
Japan as Ha-40 by Kawasaki's Akashi motor plant. It was planned to
create two airframes - a heavily armed Ki-60 intended for offensive
operations at low and medium ceilings, as well as a more agile and
lightly armed Ki-61.
Although the construction of the Ki-60 was considered a priority and
work on it started a few months earlier, the Ki-61 contained the
conclusions from the unsuccessful Ki-60 tests. Ultimately, the younger
fighter entered the service.
The Ki-61 engine mounting was constructed as an integral part of the
fuselage, so it was only possible to remove the top and bottom covers,
which was quite an unique solution. There were ammunition boxes behind
the engine firewall for two 12.7 mm Ho-103 machine guns. It was a
relatively light weapon, but very fast-firing. The supply of ammunition
was only 250 rounds for a barell. The weaponry was supplemented by a
pair of wing machine guns or cannons (depending on the version). The
pilot was protected by an armored windscreen and a 13 mm thick steel
plate behind the seat. The engine and oil radiators were placed under
the fuselage