Just as the Allies were keen to gather as much information as they could on German rocket and jet technology during World War Two, the Japanese were likewise seeking this very same technology to aid their war effort. Their need was out of desperation, being constantly pounded by Allied bombing raids and rapidly losing territory they too looked towards any available Wunderwaffe (“wonder-weapon”) Germany could provide to try and stem the tide. Following a 1943 demonstration given to Japanese Army and Navy attaches in Germany, the diminutive, yet incredibly fast Messerschmitt Me-163 Komet rocket interceptor was one such weapon they wanted to pursue.
Mitsubishi J8M Shusui / Ki-200
The Mitsubishi J8M Shusui (“Autumn Water” which also relates poetically to “Sharp Sword” and the swishing sound a sword makes) was a joint Imperial Japanese Navy and Army project using the Messerschmitt Me-163 as a basis for the design (the army variant was designated Ki-200). The Japanese were meant to licence-build Me-163 variants but getting complete airframes and parts shipped by submarine proved problematic when the Japanese submarine RO-501 Satsuki (ex U-Boat U-1224) carrying a complete airframe and possibly the two sets of sub-assemblies was sunk by Allied ships en route in the Atlantic in May 1944. A second Japanese submarine I-29 Matsu with 3 rocket motors, blueprints and manufacturer manuals onboard made it to Singapore in July 1944 and the cargo was quickly flown to Japan (for redundancy purposes two submarines were used to split the airframe from the motors and manuals with RO-501 departing in March 1944 and I-29 in April 1944).
The Japanese then had to reverse engineer the aircraft using a flight operations manual and other documentation that had been provided under the deal with Germany (they paid Germany a 20 million Reichsmark licence fee for access to this technology! This was approximately $8 million USD). An impressive effort to develop such a radical piece of technology with few physical components to work from!
The Japanese developed their own variant of the German Walter HWK 109-509A rocket motor known as the Toku-Ro.2 (KR10). It was a bi-fuel rocket motor that produced 3,307 lb of thrust which was a little less powerful than the German motor (3,800 lb of thrust). The Toku-Ro.2 (KR10) enabled the J8M1 to reach a maximum speed of 900 km/h (559 mph) which was 59 km/h (37 mph) slower than the Me-163B production model. Regardless, it was still incredibly fast for the day!
The armament was also modified to include 2 x 30mm cannons of Japanese origin that had a higher muzzle velocity than the German Mk 108 30mm cannon (540 meters per second). The Imperial Japanese Army Ki-200 variant was fitted with Type 5 30mm cannons that had a rate of fire of 450 rounds per minute and a muzzle velocity of 720 metres per second. The Imperial Japanese Navy J8M1 was fitted with lighter Ho-105 30mm cannons that provided a rate of fire 400 rounds per minute with a muzzle velocity of 750 metres per second. Japanese radios and batteries were also fitted and although similar in appearance to the Me-163 the airframe of the J8M varied slightly to accommodate the different equipment fitted.
7 J8M production aircraft were manufactured by Mitsubishi before the end of World War Two. The first J8M1 was completed in December 1944 (quite fast considering the I-29 submarine only arrived in Singapore in July 1944) but a working rocket motor was not available until July 1945. The variants were the J8M1/Ki-200 for the IJN/IJA, the J8M2 for the IJN with a longer range and only 1 x 30mm cannon, and there was also the planned J8M3/Ki-202 for the IJN/IJA which had an extended fuselage, extended wings and a longer range.
Given the radical leap in performance and handling from traditional piston engine fighter aircraft to a tailless rocket powered interceptor, up to 50 – 60 Kugisho / Yokosuka MXY8 / Ku-13 Akikusa (“Autumn Grass”) wooden glider variants were produced for pilot training and unpowered flight testing. The first glider flew on December 8th, 1944.
Despite the issues experienced in Germany the Japanese continued with the J8M program and used the same highly volatile German propellants of T-Stoff oxidizer (hydrogen peroxide) and C-Stoff (methanol-hydrazine) to create rocket fuel which was highly explosive, highly corrosive and deadly to touch. They were known as Ko and Otsu in Japanese.
Like the Me-163 the J8M1 had enough fuel for around 7.5 minutes of powered flight. As with the Me-163 it was designed to jettison the wheels after take-off and the plan once operational would have been for it to get there fast, hit the Allied bombers hard, then glide back to land on the skid and hopefully get home alive without any explosions (if the volatile fuel was onboard there was always a high risk of explosion, especially during landing)!
The first unpowered flight of an Imperial Japanese Navy J8M1 Shusui was completed on January 8th, 1945 (the aircraft used were known as “heavy gliders” to differentiate them from the Akikusa gliders). Then the first powered flight of a J8M1 was conducted on July 7th, 1945 but a fuel flow issue caused it to lose control and crash, bursting into flames (that fuel was volatile) and the aircraft was damaged beyond repair. 1 day later pilot Lieutenant Commander Toyohiko Inuzuka died from his injuries sustained in the crash. Shortly after the crash 2 more rocket motors exploded on ground testing, leaving only 1 rocket motor available which was owned by the Japanese Imperial Army.
These setbacks along with ongoing Allied bombing of the factory obviously delayed the production of airframes and the flight test program. One month later the atomic bombs were dropped on Hiroshima (August 6th, 1945) and Nagasaki (August 9th, 1945) and a few days later Japan agreed to surrender. Japanese representatives formally signed the unconditional surrender document aboard the USS Missouri on September 2nd, 1945 and with only 7 airframes completed, that was the end of the J8M program (unrealistically they had apparently planned to produce at least 3,600 J8M/Ki-200 variants by March 1946!).
Only 2 Mitsubishi J8M1 Shusui survive today. 1 is in the United States and the other in Japan. To date I have only seen the Chino example in person. It is interesting to see it in its orange livery (the IJN painted training and prototype aircraft in this highly visible scheme) and makes you think about the extreme efforts Germany and Japan had to take to implement such a dangerous and desperate project (I can only imagine what would have happened with such aircraft on Kamikaze missions)!
Planes of Fame Air Museum in Chino, California has a complete original captured Imperial Japanese Navy J8M1 on display. It was 1 of 2 bought back from Japan in 1945 for evaluation by the USAAF and US Navy respectively (neither were eventually flown). The other J8M1 was scrapped by the US Navy sometime after October 1946.
The Mitsubishi Heavy Industry Museum at the Komaki Plant near Nagoya, Japan has an interesting J8M1 on display. In the 1960’s the incomplete, damaged J8M1 airframe was discovered in a cave in Japan (a bit different from the normal “barn find”). Until 1999 it was displayed as it was at a Japanese Air Self Defense Forces (JASDF) base near Gifu. Mitsubishi began a restoration project in 1999 and today it is on display at the Mitsubishi museum in a light green livery but only the fuselage is original, the remainder is made up of replica parts.
The Mitsubishi J8M1 Shusui provides another interesting yet flawed chapter in aviation history. Rocket powered aircraft were still experimented with in the early years of the Cold War but ultimately jet technology proved to be the way to go forward.