Japanese Wonder Weapons

Posted on Tue, August 11, 2020
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Imagine it’s 1945, but a different, counterfactual 1945. World War II rages on. The U.S. strategic bombing campaign is escalating in intensity as its attempts to destroy the enemy’s means of production face increasingly determined resistance. Unexpectedly, American forces are encountering radically new and dangerous foreign aircraft. Generations of exotic, high-performance propeller-driven aircraft are challenging the best the U.S. can produce. More ominously, revolutionary jet-powered and rocket-powered fighters are wreaking havoc with American bombers and fighters while sophisticated guided missiles strike hard against the Allies. These last-minute “wonder weapons” are changing the momentum of the war and threaten to prolong this deadly conflict or even overturn what was widely seen as a decided Allied victory. Is this the technologically-advanced Germany as envisioned by countless “what-if” historians? No, it’s actually Japan as it would have been if enough of its planned new weapons had successfully taken to the skies in sufficient numbers to make a difference. 

Thankfully for the Allies, the scenario described above didn’t happen. In reality, Japan was running out of raw materials, skilled manpower, and time. Nonetheless, it was developing a host of advanced aircraft in the closing months of the war in hopes of stopping the relentlessly encroaching Allies. Faced with the challenge of superb American fighters and bombers, Japanese aircraft manufacturers first looked to modifying existing designs and creating new aircraft that incorporated high-powered, turbo-, and supercharged engines, comparable or superior to America’s best. Already the Imperial Japanese Army Air Force was operating the superlative Nakajima Ki-84 (Allied name Frank), a fighter that was a match for the North American P-51D, in China and the Philippines. But better aircraft were necessary if Japan was to counter the growing Allied threat, especially from the B-29s that were striking at the heart of the country. 

Advanced Propeller-Driven Aircraft

To face this challenge, the Nakajima Aircraft Company turned its attention to building the Ki-87, a high-altitude, heavily armed fighter powered by a single 2,400 horsepower turbosupercharged engine. It had a 440 mile per hour top speed, but engine problems delayed production and only one prototype was produced. Meanwhile, Tachikawa built its own similar looking fighter, the Ki-94-II, that had an estimated top speed of 450 miles per hour. It seemed promising and an order was placed for 18 service test aircraft. But the first flight was scheduled for August 18, 1945, three days after Japan surrendered. 

Aircraft on display at museum

The Kyushu J7W1 Shinden (Magnificent Lightning) on the ground, circa 1945

There were many other advanced propeller-driven fighters under construction or on the drawing board from Kawasaki and Mitsubishi during this time. But perhaps the most intriguing design was the Kyushu J7W1 Shinden, a canard design driving a six-bladed pusher propeller built for the Imperial Japanese Navy. With its engine in the rear and its elevators in the nose, the J7W1 was the only canard design ordered into production by any combatant during the war. Navy Captain Masaoki Tsuruno conceived the idea with the hope that, when developed, a jet engine could replace the 2,130 horsepower Mitsubishi 18-cylinder radial. In the meantime, construction was authorized in June 1944 for this desperately-needed high-altitude fighter. The first prototype was ready 10 months later. Unfortunately for Japan, engine and propeller vibration problems delayed flight tests until early August 1945, so only two were built. With an estimated top speed of 466 miles per hour, the Shinden would have been a formidable opponent, the jet-powered version (J7W2) even more so. 

Nakajima Kikka (Orange Blossom)

Left side view of a Nakajima Kikka (Orange Blossom) jet fighter on the ground before its second (but aborted) flight, August 11, 1945. The pilot, Lt. Cmdr. Susumu Takaoka, is seated in the cockpit, and the ground crew is seen ahead of wing and standing near the tail.

Jet Engine Technology

It seems there was no area of an aircraft that Japanese engineers were not willing to tweak and change, and jet engine technology was no exception.  In September 1944, design work began on the Nakajima Kikka, the only Japanese jet-powered aircraft to fly during the war. Based loosely on the outline of the Messerschmitt Me 262, the Kikka was smaller and built with folding wings to hide it in caves. When the Ne-12 turbojet engines failed to produce enough thrust, imaginative engineers designed and built the Ne-20 engine, based solely on photographs of the German BMW 003. Producing 1,047 pounds of thrust each, the Kikka was fitted with two engines that gave the aircraft the requisite top speed of 435 miles per hour. The Kikka’s first flight came on August 7, 1945, another example of “too little, too late”. A second prototype was also built but never flown with 18 others under construction. A faster version was envisioned with two Ne-130 engines, which were to produce twice the thrust, but the war ended before tests were made. 

Aircraft

Three-quarter left rear view of Mitsubishi MXY8 Akigusa (Autumn Grass), the glider prototype of J8M Shusui, built by Dai-Ichi Kaigun Koku Gijitsusho. 

Rocket-Powered Interceptors

Potentially even more dangerous to the Allies was the development of rocket-powered interceptors. In late 1943, Japanese officials became concerned about the impending threat from Boeing B-29 Superfortresses. Knowing that Japan did not have an interceptor that could attack the B-29s above 30,000 feet, the Japanese Military Attachés in Berlin acquired the manufacturing rights for the revolutionary Messerschmitt Me 163 rocket-powered interceptor and its Walter HWK 109-509 engine. The Me 163 could fly 596 miles per hour – almost 200 miles per hour faster than any Allied fighter - and could climb at an astounding rate of 10,000 feet per minute. Although hampered by its short range and 10-minute duration because of its novel engine, the Me 163 appeared to be the ideal solution to the B-29 problem. 

Plans for the Me-163 were shipped on two U-boats, one of which was sunk, leaving the Japanese military with only rudimentary data. Undeterred, in July 1944 the Japanese Navy ordered Mitsubishi to develop its own version of the aircraft designated the J8M and, in a rare example of interservice cooperation, an Army variant known as the Ki-200. Engineer Mijiro Takahashi led the project, producing a glider version by December. The glide tests were successful, and the first J8M was completed in June 1945.  The aircraft’s first flight ended in a fatal crash and modifications to the propulsion system were not completed before the war ended.

Kamikaze

From October 1944, during the U.S. liberation of the Philippines, until the end of the conflict, the Allies encountered a deadly and effective new weapon: the kamikaze. Hundreds of Japanese pilots volunteered to sacrifice their lives by crashing bomb-laden aircraft into American and British naval forces. The kamikaze were essentially guided missiles controlled by a sophisticated computer – a human being. Most of the aircraft were conventional fighters and bombers, but the Japanese Navy had also developed the Ohka Model 11, a rocket-powered, human-guided, flying bomb that was designed to fly beneath a Mitsubishi G4M “Betty” bomber until close to the U.S. fleet. Dropped from the bomber, the pilot of the Ohka would glide down, ignite the rocket engine, and dive into its target. Very few Ohkas ever made it near the U.S. fleet as patrolling U.S. fighters shot down most of the “Bettys” before they could get into range to launch their Ohkas. 

Single-seat, all-metal monocoque construction with a conventional layout, twin wings, and twin vertical fins and rudders.

Kugisho MXY7 Ohka (Cherry Blossom) 22 on display in the Steven F. Udvar-Hazy Center.

To address this problem, the Japanese Navy ordered the design of a longer-ranged jet-powered version, known as the Ohka Model 22. Powered by a Tsu-11 rudimentary turbojet, the Model 22 was designed to fly into battle underneath a Yokosuka P1Y1 bomber, which was much faster than the Betty. It was hoped that the speed of the P1Y1 and the extra range of the Model 22 would allow attacks to be launched outside of patrolling U.S. naval fighters. In the end, fifty Ohka Model 22s were built but none were ever launched. An improved version, the Model 33 was to have the more powerful Ne-20 turbojet for extra speed and range and was to be carried by a massive four-engine heavy bomber under development, the Nakajima G8N1 “Rita.” Neither the Model 33 nor the “Rita” were finished in time. 

aircraft

Right side view of a US captured Nakajima Ki-115 Tsurugi on the ground.

Desperate times require desperate measures. While the Japanese aviation industry was working hard to create new, more technologically advanced aircraft and weapons, a shortage of materials and skilled workers forced the industry and the military to attempt more elementary ideas. Accordingly, in January 1945, the Japanese Army ordered Nakajima to create a simple, easy-to-build suicide aircraft that could be mass produced in enough numbers to stop the coming Allied invasion of Japan. Built of wood and steel, and capable of using a variety of existing radial engines, the Ki 115 Tsurugi prototype was produced in only three months. It could carry a 1,700-pound bomb and jettison its landing gear for its one-way flight. Poor ground handling and difficult flying characteristics took three months to solve and, although 104 were built, none flew in combat.  

The potential capabilities and success of these wonder weapons was frightening; who knows what would have happened if these aircraft had entered service? Nevertheless, the Allies’ relentless B-29 bombing and mining campaign and the extraordinarily successful naval blockade cut off Japan’s vital fuel and resources while simultaneously destroying Japanese factories and infrastructure, rendering the fate of Japan’s wonder weapons moot.

Kyushu J7W1 Shinden (Magnificent Lightning) (A19600333000)

Kyushu J7W1 Shinden (Magnificent Lightning) on display in the Steven F. Udvar-Hazy Center.

The Smithsonian’s National Air and Space Museum is fortunate to preserve several of these fascinating aircraft. Among the many Japanese artifacts are the sole surviving Kyushu J7W1 Shinden, the last Nakajima Kikka, the only Ohka Model 22, and one of four remaining Nakajima Tsurugis. 

Japanese Jet Aircraft

One-half right front view of the Nakajima Kikka (Orange Blossom) jet fighter on display in the Steven F. Udvar-Hazy.

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