Empire of Japan (1943)
Experimental Glider Tank – One Mock-up Model

While tanks can provide excellent offensive firepower, they can’t always be easily transported to where they are needed. In the case of Japan during WW2, this was usually achieved by using ships and rail lines to transport them to where they were needed. Facing difficult terrain and disrupted shipping routes, the concept of a flying tank became a promising concept to the Japanese military hierarchy. By transporting tanks via the air, they could potentially offer benefits to the airborne troops, who were often left without proper heavy support. An exploration of this concept would lead to the creation of the Maeda Ku-6 tank glider.

The Concept of Airborne Operations

The practice of dropping airborne troops behind enemy lines offers many tactical advantages, as they can attack weak points and enemy supply lines. This in turn would force the opposing side to redistribute its own forces away from the front to deal with this problem. On the other hand, airborne forces often lack proper artillery or armor support, making them vulnerable to well-equipped and directed enemies. Some nation armies responded to this by employing glider transportable light field artillery and even recoilless, high caliber guns. Transporting armored vehicles proved a more daring task to implement. Most tanks could not be easily carried inside a transport plane or even parachuted due to their weight and size. The American and British responded by developing lightly armored and armed tanks, such as the M22 Locust or the Light Tank Mk VII Tetrarch. The Soviet Union, on the other hand, designed an auxiliary glider contraption that would be used to transport a heavier tank, the Antonov A-40. This principle would also be tested by the Japanese Army during the war, which led to the creation of the Maeda Ku-6 project.

Airborne Japan

The Japanese began the development of cargo glider designs for military use in 1937. Following the successful use of gliders by the Germans during their conquest of the West in May 1940, the Imperial Japanese Army began developing new gliders in June 1940. In response to this, the Imperial Japanese Navy began its own project soon after. In Japanese terminology, these were designated Kakku (English: to glide).

Both the IJA and IJN had and used parachute infantry units. It is important to note that these were relatively small units that were rarely employed in their intended role. For these reasons, their equipment was more or less the same as that of ordinary infantry formations. They saw the most active service during the fight for the Dutch East Indies in 1942. These were mainly used to capture various vital strategic points, such as airfields or weakly defended positions deep in the enemy’s rear line. Following the end of this campaign, the Japanese did not use paratrooper units in their primary role.

Japanese paratrooper IJN units had two notable deployments: in the successful Battle of Manado from 11th to the the12th January 1942, on Celebes Island, also known as Sulawesi, and in the Battle of Timor from19th February 1942-10th February 1943, where IJN paratroopers suffered heavy casualties. Their IJA counterparts were used more as a commando unit and were only ever airdropped during the invasion of Sumatra in February 1942.

In 1943, attempts were made to increase their firepower, though, it is unclear how much impact the experiences from the airborne operations of February 1942 had. It was proposed to use specially designed glider tanks that could be flown to their designated target and thus provide necessary firepower to otherwise weakly armed paratrooper formations. In addition, this vehicle could be airlifted to any other theater of war without a need for them to be transported by ships, which were by this time, seriously endangered by the US Navy.

The Maeda Ku-6

The project was initiated by the Army Head Aviation Office in collaboration with the Fourth Army Research Center. The first drawings of this new design were soon ready and were allocated to the Maeda research center for the construction of a working prototype. In the early stage of development, the new tank was to be transported by a specially designed glider. But as Maeda was unable to create a glider that could transport a light tank, and so another solution was needed. Maeda engineers suggested another approach to this problem. As no glider could be developed to carry a tank, maybe the tank itself could be modified to use a glider.

While Maeda was responsible for the glider development, the design of the tank was given to Mitsubishi Heavy Industries. It is unclear if it was a completely new tank design or if Mitsubishi reused some of the existing vehicles that were in service. According to the Japanese Army and Navy Aircraft Complete Guide, the Type 98 light tank was used for the project. This tank was intended as a replacement for the Type 95 Ha-Go, but this was never achieved as it was built too late and in very small numbers.

Name of the Project

According to E. M. Dyer, the new light tank was designated as So-Ra (Sora-Sha), which could be translated as the “sky” or “air” tank. The whole project would be designated Kuro-Sha, with the Ku and Ro, meaning the number ‘6’, taken from the Ku-6 glider designation. Lastly, the Sha stands for “tank”. An older source, J. E. Mrazek, mentions that the tank design originated in late 1939. According to Mrazek, the tank was initially designated ‘special Tank project 3’. It received the Sora-Sha designation before being changed to Kuro-Sha (English: Black Vehicle).

Technical Specification

The Ku-6 was designed as a tank transport glider. While not specified, it is likely that the Ku-6 would have been made out of wood. Due to the losses of the original documents, not much is known about its overall design. Over the years, historians based on available information devised two different designs of how this contraption may have looked.

The tank itself, due to its nature of use, had to be as light as possible. This means it would have been lightly armored and armed. The So-Ra’s total weight was slightly above 3 tonnes and would have been operated by two crew members. The driver was positioned in the front of the vehicle. He was also responsible for piloting the whole glider. Behind him, in the turret, was the commander, who was responsible for operating the main armament. This small crew would have greatly affected the tank’s overall performance. Given the limitation in size and weight, adding more crew members was not possible. In normal circumstances, the driver’s vision ports would have been small and protected. In this case, he would need to have a good and unobscured overall view of his surroundings. For this reason, he was to be provided with three large viewports. The armor was to be less than 12 mm thick. While its armament consisted of one 37 mm gun, along with a machine gun, a possible installation of a flame thrower was also considered.

As the tracks would cause massive drag during take-off, specially designed sleds would be attached to them to facilitate an easier take-off. According to the first proposals, the tank itself was designed to act as an improvised glider fuselage and the wings and the tail assembly would be attached to it.  The tank crews would be provided with wired controls installed inside the vehicle in order to pilot it. In front of the tank, a towing cable would be added to connect it to the glider tug.

The second version is completely different. Above the tank, a larger wing with a twin tail boom was added. These two components would be connected by struts. In both cases, once the tank hit the ground, the wing assemblies could be easily removed, which meant that the tank could immediately go into action with relative ease.

It is unspecified which material would be used during the whole wing assembly. Given its rather late introduction and Japanese limited resources at this point, wood would likely be used.  With the whole wing assembly, the Ku-6 had a length of between 12.8 to 15 m (depending on the source) with a width of 22 m and a height of 3 m. The wing area was around 60 m².

The maximum towing speed at heights of 4 km was 250 km/h. The maximum speed that could be achieved during the gliding flight itself was 174 km/h. The decent speed at 4 km altitude was 2.8 sec/m while at lower heights closer to the ground it was 2.6 sec/m. It is important to note that these are projected figures.

Testing and Project’s Fate

Due to the slow pace of work, the first operational glider prototype was completed in 1945. The tank itself was not ready by this time. As a temporary solution, a wooden mock-up of it with ballast was intended to be used instead. The prototype was taken to the sky by a Mitsubishi Ki-21 medium bomber. Almost from the start, the Ku-6 (according to E. M. Dyer the second variant was used) proved to have poor overall flight characteristics, and the pilot had a poor view. Lastly, as it was specially designed to carry the So-Ra, its transport capacity for other vehicles was very limited. The IJA officials quickly became disinterested in the Ku-6, focusing instead on the Ku-7 general purpose glider which looked more promising. Another aspect that we must take into account was the poor state of the Japanese Army in 1945. By this point, it was so battered and depleted, that undertaking an airborne operation was an impossible task. In the end, the Ku-6 would be terminated and the fate of the single prototype is unknown, but it was either scrapped or lost during Allied bombing raids.

Conclusion

The Ku-6 seems like an interesting concept that could have offered a number of benefits to the Japanese in the early years of the Pacific theater. By 1943, when the project was initiated, the war situation for Japan had rapidly deteriorated, with the Allies pressing on all sides. In reality, the Ku-6 proved to be too flawed in design. It was difficult to control and the pilot had poor visibility. Given that it was a glider, it would make an easy target for Allied fighters which, by its construction time, had almost complete air supremacy.

Credits

• Written by Marko P.
• Edited by Henry H. & Medicman11.
• Illustrated by Godzilla

Sources

• D. Nešić (2008), Naoružanje Drugog Svetsko Rata-Japan, Beograd
• E. M. Dyer (2009) Japanese Secret Projects Experimental Aircraft of the IJA and IJN 1939-1945, Midland
• J. E. Mrazek (1977) Fighting Gliders of World War II, ST Martin Press
• S. J. Zaloga (2007) Japanese tanks 1939-45, New Vanguard
• Tomio Hara’s Japanese Tanks 1978
• Japanese Army and Navy Aircraft Complete Guide
• L. Ness (2015) Rikugun Guide To Japanese Ground Forces 1937-1945, Helion and Company