The Type 3 Fighter "Hien" (Ki-61) was the only Japanese fighter aircraft equipped with a liquid-cooled engine to see active service during the Pacific War. Through rigorous efforts to reduce drag and weight, it was completed as a well-balanced aircraft capable of maximizing both speed and maneuverability—earning it the classification of a "medium fighter."
It was officially adopted in 1943 (Showa 18) but suffered from production issues due to Japan’s limited industrial base and frequent malfunctions of the Ha-40 liquid-cooled engine caused by unfamiliar maintenance practices. Despite these challenges, the Hien saw combat in the Philippines, New Guinea, and in homeland air defense operations. In particular, during the defense of the Japanese mainland, proper parts supply and the work of experienced maintenance crews helped maintain a high operational rate. Its superior high-altitude performance compared to other Japanese aircraft made it effective in battles against B-29 bombers.
Notably, the 244th Flight Regiment, led by Captain Teruhiko Kobayashi—the youngest squadron commander in Japanese Army history—fought fiercely and claimed over 160 B-29 kills before the end of the war, making it one of the most successful units.
Specifications:
- Crew: 1
- Wingspan: 12.00 m
- Length: 8.94 m
- Height: 3.70 m
- Loaded Weight: 3,470 kg
- Engine: Ha-40 (1,100 horsepower at 4,200 m altitude)
- Maximum Speed: 580 km/h at 5,000 m altitude
- Armament: 20 mm cannons, two 12.7 mm machine guns x 2