Mitsubishi J8M (Shusui) Rocket-Powered Interceptor
The Mitsubishi J8M rocket-propelled interceptor was based on the German Messerschmitt Me 163 Komet - acquired by Japan via purchase of manufacturing rights.
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The Empire of Japan and the nation of Germany had maintained a relationship since Prussian authorities made diplomatic contact on the Japanese mainland in 1860. However, World War 1 (1914-1918) delayed a forged alliance when Japan found itself against the German Empire and claimed several German territories in the Asia-Pacific region. During the interwar years that followed, the two nations would adopt similar militaristic-driven governments that controlled both political and military policy and this direction brought the two nations into agreement once more. Japan aligned with the Axis powers in World War 2 (1939-1945), joining Germany and Italy as principles in the fight though distances between the powers ultimately segregated combat into two defined fronts - the Pacific and European Campaigns.
During their alignment in World War 2, certain military agreements came to pass and one such resolution became availability of the technology driving the new German Messerschmitt Me 163 "Komet" rocket-powered interceptor. The Japanese government, not blind to the disastrous results of the Allied day/night bombing campaigns on Italy and Germany, understood the arrival of the high-altitude Boeing B-29 Superfortress would bring similar ruin to the Japanese mainland in time. Due to the advanced nature of the B-29, the heavy four-engined bomber could fly out of reach of available Japanese defenses including its interceptor arm. The Me 163 offered some hope - a supremely fast little aircraft outfitted with cannon armament designed exclusively to combat large bomber formations. Its rocket-powered nature ensured quick response times in achieving the required altitude prior to the bomber formation's arrival.
Of course this sort of evolutionary design came at a price for the rocket fuel powering the Walther engine allowed for just 7.5 minutes of flight time, limiting engagement to a few controlled swoops. The speed at which the Me 163 approached often led to pilots overshooting their intended targets at speed. Additionally, the German fuel mixture consisted of a highly volatile combination of "C-Stoff" (a hydrogen peroxide/methanol-hydrazine combination) mixed with an oxidizer in the form of "T-Stoff" - the mixture having a tendency to ignite and explode. Landing was accomplished by gliding onto its belly, a moment in flight which made the Me 163 extremely vulnerable to passing fighter aircraft. Regardless, the aircraft offered up massive performance benefits over traditional propeller-driven fighter types and turbojet technology was still in its infancy - leaving the Japanese Empire with little choice as to how to proceed.
The Japanese Empire secured the production rights to both the Messerschmitt airframe and the Walther HWK 509A series rocket engine that powered it in 1943. Localized production of both would make the Me 163 immediately available to Japanese aviators while at the same time providing a technological advantage of sorts concerning advanced rocket technology for Japanese engineers to evolve on their own. The Me 163 was already being utilized operationally over German territory with limited success and this showed the Japanese that the weapon could be a viable solution for their own defensive war being forced by the Americans in the Pacific. German factories produced some 300 Me 163 Komets before the end of the war and these claimed between 9 and 16 air victories according to conflicting records.
A complete Me 163 airframe, Messerschmitt technical blueprints and three example Walther rocket engines were stowed aboard two separate Japanese Navy submarines - RO-501 and I-29. RO-501 left Germany (Kiel) on March 30th, 1944 while the I-29 departed the French port of Lorient on April 16th, 1944. While en route, RO-501 was targeted, attacked and sunk by American forces on May 13th - its cargo lost to the deep. The I-29 managed to safely navigate to Singapore with its Me 163 blueprints and Walther engine examples intact.
Despite the loss of the RO-501 and its Me 163-related goods, the Japanese understood the German text and drawings enough to attempt to engineer the aircraft from scratch beginning in July of 1944. The storied concern of Mitsubishi was charged with developing the rocket-powered interceptor for use by the Imperial Japanese Army and the Navy - the project to be led by Mijiro Takahashi. The Army version would be designated as the "Ki-200" while the Navy mount was to be known as the J8M "Shusui" (translating to "Autumn Water", "Sword Stroke" and "Sharp Sword").
Mitsubishi produced a powerless glider to handle in-flight data gathering while also working on flyable prototype to help expedite development. A mockup of the latter was completed in September of 1944 and the powerless glider appeared in December. Naturally, the glider was put to the air first with a test pilot in the cockpit while being towed by a lead aircraft. The control system and handling was found to be adequate and development continued. Yokosuka was commissioned for construction of two more gliders for additional testing while work then began on a second flyable prototype. Testing proved the Japanese copy of the Walther engine somewhat underpowered compared to the original performance figures achieved by Germany though this could be offset with utilization of a lighter airframe. With data in hand and test flights proving the design sound, a consortium led by Mitsubishi (to include Nissan and Fuji) ramped up for airframe production while Yokosuka was gearing its lines for the Walther rocket engine as the "Ro.2".