Kawasaki Ki-61 Hien
The Kawasaki Ki-61 Hien ("Swallow"), known to the Allies by the reporting name "Tony", was a single-seat fighter built by Kawasaki for the Imperial Japanese Army Air Service in the Second World War. Unusually for a Japanese design it was powered by a liquid-cooled engine, the Ha-40, a licence-built Daimler-Benz DB 601, and its long nose led Allied intelligence to mistake it first for a German and then for an Italian aircraft. Fast and well protected by Japanese standards, it fought from New Guinea in 1943 to the defence of Japan in 1945, but the Ha-40 proved unreliable and hard to maintain in the field. Only a handful of airframes survive.
Why It Mattered
The Kawasaki Ki-61 Hien — "Swallow" — entered service as the Army Type 3 Fighter, and it stood apart from every other Japanese fighter of the Second World War. It was the only mass-produced Japanese fighter powered by a liquid-cooled engine: the Ha-40, Kawasaki's licence-built version of the German Daimler-Benz DB 601. Where Japanese fighters had prized lightness and turning ability, the Ki-61 offered speed, a strong dive, self-sealing fuel tanks and armour for the pilot. Its long, low nose looked European rather than Japanese, so Allied intelligence first took it for a licence-built Messerschmitt Bf 109, then for an Italian design, and gave it the reporting name "Tony". Its weakness was baked in from the start: the Ha-40 ran hotter and proved less reliable than the German engine it copied.
Design Notes
Takeo Doi and Shin Owada led the Kawasaki team that designed the Ki-61 around the Ha-40, one of two fighters the Army ordered from Kawasaki in February 1940, alongside the heavier Ki-60. When the Ki-60 disappointed, work on it was abandoned and Kawasaki concentrated on the lighter Ki-61, giving it a slimmer fuselage and a longer, higher-aspect-ratio wing that reduced wing loading. The first prototype flew early in December 1941, and in competitive trials the Ki-61 was the fastest aircraft tested — ahead of an imported Bf 109E, a captured P-40E and its Japanese contemporaries — and was out-manoeuvred only by the Ki-43. Armament strengthened as production went on, and the most common version, the Ki-61-I KAIc, carried two 20 mm Ho-5 cannon in the fuselage and two 12.7 mm machine guns in the wings. Production of the Ki-61-I ran until January 1945 and totalled somewhere between 2,654 and 2,734 aircraft. A developed version, the Ki-61-II, flew with the more powerful but less reliable Ha-140, yet only 99 of its 374 airframes ever received that engine; after American bombing destroyed the Akashi engine factory, the remaining 275 engineless airframes were completed with radial engines as Ki-100s.
Operational History
The Military Aviation Museum's history of the type says the Ki-61 first saw combat over Yokohama during the Doolittle Raid of April 1942. It entered Army service in February 1943 with a training unit in Japan, and the first operational units, the 68th and 78th Sentais, moved south to Rabaul and New Guinea that spring. The transfer itself was costly: on one delivery flight 18 of 30 aircraft were lost after straying off course, and both units reached Rabaul already under strength. In New Guinea the Ki-61's armour and robust build told in its favour: it could out-dive the P-38s, P-39s and P-40s it met, and out-manoeuvre any Allied fighter until the P-51 Mustang and F6F Hellcat entered service. But the theatre defeated its logistics: the Ha-40 could not be overhauled in the field, jungle conditions hampered operations, and only 5% of Army pilots with more than 300 hours' flying time survived the New Guinea fighting. The Ki-61 next fought in large numbers in the defence of the Philippines, then over Formosa and Okinawa, and finally in the defence of the home islands against B-29s, which the Ki-61-I could only just reach at their operating altitude; some pilots resorted to ramming attacks. American accounts credit Lt William Shomo with destroying six Ki-61s and a G4M bomber in a single engagement near Tuguegarao in the Philippines on 11 January 1945, an action for which he was awarded the Medal of Honor. The cost fell on the units: in the Philippines, the 55th Sentai had lost all of its pilots by the end of November 1944.
Afterlife
Only a handful of Ki-61s survive today. The Gifu-Kakamigahara Air and Space Museum in Japan exhibits a restored Ki-61-II-Kai, construction number 6117, which Kawasaki Heavy Industries restored in 2015–16 after its earlier display at the Chiran Peace Museum. Two more airframes are with AvSpecs at Ardmore in New Zealand: number 299, being restored to static display for the Papua New Guinea National Museum, and number 640, being restored to airworthy condition. Number 640 is the Military Aviation Museum's aircraft: the museum recounts that it was built at Kakamigahara in November 1943, force-landed in kunai grass near the village of Yiliwe in New Guinea, and lay largely undisturbed until recovery began in 1975. Another Ki-61, number 379, is in storage at Fantasy of Flight in Florida.