Nakajima Ki-115 Tsurugi
The Nakajima Ki-115 Tsurugi was a single-seat special-attack aircraft built by Nakajima in the last months of the Second World War. Ordered by the Japanese Army in January 1945, it was designed for cheap mass production by semi-skilled workers, from steel, wood and aluminum, with a landing gear that dropped away after takeoff and a single bomb of up to 800 kg. It first flew in March 1945; 104 were built by Nakajima and one by the Mitaka institute, but none was used operationally. The Smithsonian's example, displayed on loan at the Pima Air & Space Museum, is believed to be the only survivor.
Why It Mattered
The Nakajima Ki-115 Tsurugi was an aeroplane designed to be destroyed: its pilot was to dive it, bomb and all, into an Allied warship. Japanese commanders settled on organised special attacks in the autumn of 1944, as Allied forces ground down Japanese strength across the Pacific. The attacks hurt the U.S. Navy badly, but they consumed ordinary combat aircraft that Japan could no longer replace. The response was a class of simple, cheap, purpose-built machines that pilots with minimal training could take off, fly to a target and dive. The Ki-115, the Army's version, was meant for the invasion fleet expected against the home islands, an invasion that never came.
Design Notes
In January 1945 the Army ordered Nakajima to produce a special attacker carrying one bomb, reaching at least 515 kph, and above all simple to build. Engineer Aori Kunihiro led the design, assisted by staff from the Mitaka Research Institute and the Ota Manufacturing company. Simplicity was forced by the workforce: the factories now relied on semi-skilled students working part-time shifts. The airframe mixed materials as they came to hand: a steel frame and skin for the fuselage, a cowling rolled from sheet tin, a fabric-covered wooden tail, and wings built wholly of aluminum. Its fixed gear was two steel struts bolted to the wing, without shock absorbers, and the whole structure was designed to drop away after takeoff. The airframe could accept several kinds of surplus radial engine, though every production aircraft used Nakajima's 14-cylinder Ha35-23. The pilot sat in an open cockpit set high above the trailing edge of the wing.
Operational History
The first prototype was ready in under two months, and published references date the first flight to March 1945. Early testing showed the aeroplane handled badly on the ground, its one serious fault. Nakajima redesigned the gear with simple shock absorbers and fitted auxiliary flaps to the inboard trailing edges of the wings. Production aircraft also carried fittings under each wing for two solid-fuel rockets, meant to add speed during the final dive on a target. With these changes the Ki-115 reached 550 kph with a bomb of up to 800 kg, and had a range of 1,200 km. Nakajima built 104 of the aircraft at two factories, and the Mitaka institute, which had helped design it, built one more. The Navy gave the type its own name, Tōka, but the naval variant and improved versions never got beyond the drawing board. No Ki-115 ever saw combat, and none was used operationally before the war ended in August 1945. Nakajima destroyed most of its records before the Allies arrived, so the details of the test programme and the planned deployment are largely lost.
Afterlife
One aircraft passed into American hands: U.S. Navy intelligence specialists probably collected it at the factory after the surrender. It was taken to the naval base at Yokosuka and shipped to the United States on one of the carriers ferrying captured Japanese aircraft back for evaluation. In 1949 the National Air Museum, today's National Air and Space Museum, added it to the collection, along with some 53 other foreign aircraft. The aircraft, serial 1002, is now on display at the Pima Air & Space Museum in Tucson, Arizona; NASM lists its own status as on loan or in storage. The Smithsonian believes its aircraft is the only Tsurugi left. A second airframe, formerly a gate guardian at Yokota Air Base, is reported to survive at a Japanese museum, but its fate is unconfirmed.