The Nakajima Ki-115 Tsuguri ("Sword") was a simplistic single-seat, single-engine suicide fighter aircraft development undertaken by the Empire of Japan in the closing month of World War 2. The type first flew in June of 1945 and was built in just 104 examples before the war formally ended her career by August of that year. Developed by the Imperial Japanese Army Air Force (IJAAF), the Ki-115 was to also be featured in the inventory of the Imperial Japanese Navy (IJN) where it was known as the "Toka" ("Wisteria Blossom").
By the middle of 1945, Adolf Hitler had committed suicide, Germany had capitulated to the might of the Allied war machine and the Axis was no more - the war in the Europe was officially over and symbolized by "VE" day. The war in the Pacific was an ongoing affair and progress was steadily made on the part of the Allies though with much blood to show for it. However, the war had ultimately closed in the shores of the Empire of Japan with all its major cities within reach of Allied fighters and bombers thanks to the capture of Iwo Jima (February) and Okinawa (April). Like Germany in the closing months of the European Campaign, it was a time of desperate measures for the island nation and the full-scale Allied invasion of the mainland was an all-too certain reality. The invasion had already garnered a codename under "Operation Downfall" and plans were being drawn up.
The amphibious invasion of the Japanese mainland would involve a massive outpouring of man and machine coming from a sea armada to be divided into two invasion forces - a southern island invasion fleet and a main island invasion fleet. Air cover was critical but so to was the logistical side of such an endeavor. The operation would need heavy support in all forms, not the least of these being the powerful Allied shipping arm that indirectly forced subsequent Japanese retreats throughout the Pacific campaign up to this point in the war. It was one thing to gain ground from the enemy with guns, tanks and planes but it was another to hold that ground indefinitely with bullets, fuel and bombs - logistics would play a key role in the intended invasion plans.
Japanese High Command looked to developing a low-cost, easy-to-use and quick-to-field suicide fighter plane to be used in the "kamikaze" role against key Allied shipping. Kamikaze's proved of some value to this point in the war for Japan but mostly as psychological terror weapons. While Allied sailors became painfully introduced to these suicidal attacks, the attacks did little to disrupt the actions of the United States Navy and British Royal Navy throughout the latter half of the war. If anything, they cost the Empire dearly in both man and material. However, it was envisioned that a great air fleet of these suicide aircraft could turn the tide of the mainland invasion in favor of the defenders, perhaps securing a favorable surrender. This sort of strategy was not lost on Hitler and his Germany - pouring funding, materials and manpower into "dead-end" projects by war's end - though only one of these designs proving suicidal in nature. For the Empire of Japan - where death for the Emperor was an honorable death - one of these last-ditch results became the Nakajima Ki-115 suicide fighter.
A "throw-away" design such as the Ki-115 attempted to make light use of material- and time-saving measures wherever possible. The fuselage was made into a cylindrical form - easier to produce than the elliptical types of more modern fighter types. Steel and wood featured heavily throughout its construction as these were deemed less strategic to the Japanese war effort. Additionally, the fuselage was designed from the outset to take on a wide variety of pre-existing engine types to help speed production along. These engines would come from the stockpile of old surplus powerplants as available. The only known powerplant to have been fitted to the Ki-115, however, became the Nakajima Ha-35 Type 23 series radial piston engine of 1,150 horsepower. All these factors lent themselves well to the speedy production effort needed to get the Ki-115 into available hands in quantity. Like German High Command in the desperate, closing months of the European Campaign, Japanese authorities were equally optimistic and projected a monthly output of 8,000 such aircraft with hundreds of factories committed to the effort.
Design of the Ki-115 was highly conventional, featuring a low-wing monoplane arrangement with a conventional tail section, engine and cockpit placement. The engine was held well forward along the streamlined cylindrical fuselage and powered a three-blade propeller system. The cockpit was fitted amidships with adequate views to the front, sides and above despite noticeable framing. The rear view was blocked substantially by way of a raised spine. Overall, however, views outside of the cockpit were noted as generally quite poor, no thanks to the long fuselage snout and cockpit placement behind the wings. Inside the cockpit, the pilot had access to a basic instrument panel as well as typical fighter controls such as a flight stick and rudder pedals. Provisions were made for a radio system though it is unknown if this feature was ever fully incorporated. But as the Ki-115 was not designed for dogfighting, much of these limitations were none too great the detriment. The fuselage tapered off into the raised empennage to which sat a traditional vertical tail fin and squared-off horizontal planes. The Ki-115 featured a conventional undercarriage made up of two single-wheeled main landing gear legs - utilizing welded steel tubing - and a tail skid. Shock absorbers were only later added to assist in ground maneuvering. Of note is that the main legs were jettisoned after take-off for a decrease in operational weight, easier production methodology and a slight increase to performance by the saved weight. As the aircraft was not expected to return home, this was a negligible sacrifice to the pilot and aircraft.
The Ki-115 was fitted with a single Nakajima Ha-35 Type 23 series radial piston engine of 1,150 horsepower. This provided for a top speed of about 342 miles per hour with a range of 746 miles. Two rocket accelerators could be added for a temporary boost in performance, particularly during the all-critical "end run" of a kamikaze flight. Overall, the Ki-115 exhibited very little in the way of respectable performance and required the capabilities of trained fighter pilots over that of any raw recruit. Testing alone led to fatal crashes during the Ki-115's short development period.
The aircraft featured no standard machine gun or cannon armament in an effort to save on weight and the simple fact that the Ki-115 was not intended as a true fighter bent on combating Allied warplanes directly. Instead, like other kamikaze aircraft, the pilot delivered a potent payload made up of a single bomb clamped to the fuselage centerline under the aircraft. This came in the form of a single 551lb, 1,102lb or 1,764lb bomb - designed to wreak the most havoc as possible during the kamikaze strike.
In the end, as feared as a kamikaze was to Allied seaman, the attacks did little in the way of disrupting shipping lanes and planned offensives. As such, projects like the Ki-115 tended to be short-lived in nature - though the official end of the war came all too soon for the Empire of Japan, finding themselves a conquered nation at the end of August 1945 following the Atomic bomb droppings on Hiroshima and Nagasaki. The war in the Pacific was now over - as was all of World War 2 - for the history books. Operational Downfall was never put into action and spared the lives of thousands of Allied marines, airmen and sailors.
The Ki-115 was never used operationally in any kamikaze actions. As with those "Secret Weapons of the Luftwaffe", it is only left to the imagination of the reader what a swarm of Ki-115 suicide fighters might have done against Allied shipping in the region. Only a single production example survived the war, this specimen now at the Garber Facility attached to the National Air and Space Museum.