Type 97 Chi-Ni

The Experimental Medium Tank Chi-Ni (試製中戦車 チニ Shisei-chū-sensha chini) was an experimental prototype Japanese medium tank. Initially proposed as a low-cost alternative to the Type 97 Chi-Ha medium tank, it was eventually passed over by its competitor.

History and development
In 1935 news had reached Japan of the United Kingdom's development of an advanced new tank, the A6 medium tank. A multi-turreted design that mounted a 47 mm tank gun and was capable of reaching speeds of 50 km/h. In comparison Japan's tank force had not undergone any significant changes in tactics or organization in six years. The country's most widely fielded medium tank, the Type 89 I-Go, while popular with troops and tank crews had begun to show its age, attempts to update the design with the Type 89B I-Go Otsu were made in 1934, but no fundamentally new design had been undertaken since. Until this point it was felt that there was no need for a new medium tank design. In comparison of the two tanks the A6 was seen as having superior offensive and defence capabilities than its closest Japanese equivalent which had begun looking obsolete to its British counterpart. The appearance of Britain's new tank design, along with reports from Manchuria of the Type 89 I-Go's inability to keep up with other motorized vehicles with its paltry 25 km/h top speed brought about plans for a replacement.

Tank designers recommended research on a new tank design, a medium tank capable of going 35 km/h and weighing 15 tons with offensive and defensive abilities greater than the Type 89 I-Go. The Chief-of-Staff Operations was not enthusiastic for the project initially. It was peace-time and the military had a limited budget to spend and thus issued peace time requirements for a new tank design. Rather than focusing on performance improvements, the Chief-of-Staff Operations made only a lighter weight the sole requirement in order to lower production costs. The finalised requirements were for a lightweight tank that was also capable of going 35 km/h. These requirement also led to the development of the Type 95 Ha-Go light tank. The Engineering Department believed that it was highly regrettable that their efforts would be devoted solely to weight reduction, so instead, two concurrent projects were built. The first plan was contracted to Mitsubishi Heavy Industries for a higher performance medium tank design which would become the Chi-Ha. The second plan was for a low weight, low cost medium tank that was to be made by the Osaka Army Arsenal which would become the Chi-Ni.

Design
The initial design requirements for the two prototypes were:

The Chi-Ni was therefore envisioned as a smaller, lighter alternative to the Chi-Ha, a medium tank closer to the original Chief-of-Staff Operations requirements than the tank design engineer's suggestions. The hull was of a monocoque design and welding was used more extensively than previous tanks (although riveting was still used). This was unlike previous Japanese tanks which were riveted around a framework. The Chi-Ni also shared the same bell crank suspension as the Chi-Ha that would continue to be use by later Japanese tanks until the end of the Second World War. The hull was designed with a streamlined silhouette to protect from shell damage. The crew of the Chi-Ni, unlike the Chi-Ha was only made up of three men, with the tank commander acting as both a gunner and loader in the small, single man turret. The turret did not have room for any coaxial machine gun. The driver was seated in the hull on the left hand side, with the third crew member, a machine gunner, was seated to right of the driver. The tank was initially planned to be armed with the Type 89 I-Gos Type 90 57 mm gun but a new tank gun was being designed at the time to replace the lower velocity gun. This improved tank gun was the Type 97 57 mm tank gun. A single, forward firing, 7.7×58mm Arisaka Type 97 machine gun was mounted in the hull. The diameter of the turret ring for both tanks was made as large as possible to allow for any future up-gunning of the tanks. The tank was powered by a 135 hp diesel engine made by Mitsubishi. There are also documents stating that the Chi-Ni was tested with a 120 hp Mitsubishi A6120VDe air-cooled diesel engine from a Type 95 Ha-Go. The Chi-Ni was also equipped with a 'tadpole tail', a tail extension attached to the back of the tank to allow it to better cross trenches. Design work for both tanks started in 1936 and both prototypes were completed by 1937, both plans exceeded or met the original requirements within reason.

Production
During the time the Chi-Ni and Chi-Ha trials and discussion were being undertaken, the China Incident occurred in 7 July 1937, sparking a war with China. The outbreak of hostilities ended the military's restriction on peacetime budgetary spending and the technically superior but costlier Chi-Ha was adopted unconditionally over the Chi-Ni. The Type 97 Chi-Ha would go on to be the most numerically important Japanese medium tank of the Second World War. Only a single Chi-Ni prototype was ever built. Even though the Chi-Ni was passed over in favour of the Chi-Ha, several individuals in the Japanese military, such as Japanese Army tank designer Lieutenant General Tomio Hara, believed that there was still potential in the design and the tank could be reused in the future as a light tank.