The Kawasaki Ki-61 Hien was a single-seat, liquid-cooled, fighter aircraft that was used by Imperial Japan during World War II.


The first production model was the Kawasaki Ki-61-I Hien, which had a 1,180 hp Kawasaki Ha-40 engine capable of propelling the Ki-61 at speeds of up to 592 km/h.[1]

The Ki-61 had a wingspan of about 10 meters and a height of 3.7 meters. The total weight of the Ki-61 was 2,210 kg and it was about 8.8 meters long while the service ceiling of the Kawasaki was about 10,000 meters. The armament of the Ki-61 consisted of four 12.7mm MGs and the capability to carry two 249.4 kg bombs.

It had a fuel capacity of about 365 liters and it had a maximum range of about 1,100 kilometers. Although, additional fuel could be carried in external drop tanks. The name Hien meant swallow and it was also classified by Imperial Japan as a Type 3 fighter. It was the only water-cooled aircraft to enter service into Imperial Japan's Airforce. The Ki-61 was codenamed "Tony" by allied forces because of the - incorrect - belief that it had come from Italian designs, although it did take some concepts from German designs.


The Kawasaki had many variants and as such had minor modifications made between many major variants including where the guns are positioned. The first of these minor variants is the Kawasaki Ki-61-Ia which had the same four 12.7mm MGs, but sometimes had two 20mm autocannons mounted in the wings. It was followed by the Ki-61-Ib which was hardly any different from the Ki-61-Ia. The Ki-61-Ic made the 20mm autocannons standard. The Kawasaki Ki-61-KAIc was the next major variant in the series.

It had the two 20mm autocanons mounted in the nose and the original armament of four MGs in the wings. This version also had the Kawasaki Ha-40 piston engine which had 5 more hp than the original engine. It weighed about 2,630 kg and it had the same altitude ceiling as the original.[2] The Kawasaki Ki-61-KAId soon followed and it had 30mm autocannons in the nose of the plane.

These cannons were meant to assist when targeting bombers. However this was the only modification made to it and it was produced in limited numbers. The Kawasaki Ki-61-II however had many new changed made to it. It was fitted with a 1,500 hp Kawasaki Ha-140Engine and larger wings. It also had an improved canopy.[3] Even though it had shown a multitude of problems during testing, it still maintained a top speed of 610 km/h. The Kawasaki Ki-61-II KAI had even larger wings and the rudder was also larger. Among the two minor variants made of it, there was the Ki-61-II KAIa and the KAIb.

The KAIb had four 20mm canons and the KAIa just had the normal armament. The Kawasaki Ki-61-III was the last variant of the series and it had a lower fuselage along with a redesigned canopy. About 3,000 of this version of the Ki-61 were made. An unofficial variant of the Ki-61, the Kawasaki Ki-100 was converted from the Kawasaki Ki-61-II KAI in a rushed job and was, in turn, arguably one of the best interceptors of WWII ever created.[4]

A Kawasaki Ki-61-I


The Kawasaki Ki-61 first began development in February 1940, when news of the war in Europe prompted the issue of development contracts to Kawasaki for two new fighter designs, both designed by Shin Owada to be powered by DB 601A engines, and designated Ki-60 and Ki-61. First flown in March 1941, the Ki-60 was eventually abandoned in favour of the lighter Ki-61, which first flew in December 1941.[5]

The Kawasaki Ki-61-I was first deployed in 1942 and it was used throughout WWII. It was one of the only Japanese aircraft that could combat the B-29 Superfortress, making it an important weapon against them. However, many were lost in B-29 raids and which forced many Japanese pilots purposely crash into B-29s as a means of defending the home islands. Alongside being used as an interceptor, the Ki-61 was used as a regular fighter by several squadrons or Sentais. It first saw combat over New Guinea where it proved to be a real threat to Allied planes. In total, about 3,000 Ki-61s were made during the war.

A shortage of liquid cooled inline engines resulted in spare airframes being adapted for fitting with the Mitsubishi Ha.112 II radial engine as the Kawasaki Ki-100.[6]


  4. Lüdeke, Alexander. Weapons of World War II. Parragon Books Ltd. (2007), Page 220
  5. Green, William. Famous Fighters of the Second World War. Purnell Book Services. 1975. Page 30
  6. Green, William - Fighters. Page 33

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