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Mitsubishi Type 89 Yi-Go Medium Tank
Technical Information

After the first Japanese tank was developed, the Type 87 Chi-I it was found to be too heavy and too slow. A light tank at 10 tons weight was designed. The development period was relatively short, due to the designers' experiences with the earlier model. Designers used Steel plate armour developed by the Nihonseikosho Company. The armour was referred to as 'Niseko steel', abbreviated as Nihonseikosho.

The design was initiated in 1925 by the Japanese Army Osaka Technical Arsenal. This was Japan's first domestic light tank project. The design was relatively conventional having been influenced by the British Vickers Mark C tank that had been purchased by Japan in 1927.

The development of the diesel engine was ordered to Mitsubishi Jukogyo Company. After efforts in two and a half years, Mitsubishi had accomplished the development of diesel engine. It was an air-cooling 120 hp diesel engine Mitsubishi A6120VD. It was installed in the Type 89 Medium Tank from the 1934 production. It was also used by the early production Type 95 Light Tank. This engine was reliable and easy to maintain.

In April 1929, the new light tank was finished. Its weight was 9.8 tons. It was designated the "Type 89 Light Tank." Later, it was re-classified as a "Medium Tank" because the weight increased to over 10 tons due to several improvements. The production of Type 89 Tank started in 1931 and it became the main tank of the Imperial Japanese Army.

The Yi-Go was first tank that was mass-produced in Japan. The early model, "Ko," had a gas engine and mounted a machine gun on the right side of the hull.

Wartime Usage
Used during the Second Sino-Japanese War, Nomonhan Incident and the Second World War.

Type 89 Ko Model
The initial production model had a gasoline engine and mounted a machine gun on the right side of the hull. As this design could only attain 15.5 km/hr, and was also limited by the severe winter climate in northern China. A total of 220 units were produced prior to 1934.

Type 89 Otsu Model
The later model "Otsu" had an air cooled diesel 120 PS/1800 rpm engine and mounted a machine gun on the left side of the hull. The diesel engine had several advantages, notably reduced vulnerability to fire and better fuel economy. This Otsu version was the first diesel-powered tank to be mass-produced in the world.

The improved model had a new gun turret design complete with a cupola for the commander, and with the machine gun relocated to the left side of the hull. The multiple armor plates of the front hull were replaced by a single shallow-sloped frontal armor plate which provided more protection for the driver. However, the major difference between the versions was the Mitsubishi air-cooled 6-cylinder diesel engine, which had several advantages, notably reduced vulnerability to fire and better fuel economy. A diesel engine was also preferred by the Japanese Army because more diesel fuel than gasoline could be produced per barrel of oil. A total of 189 Otsu units were produced.

Built by Mitsubishi from 1932 to 1942 and used during the Second World War.
Type 89 Ko Model: 220
Type 89 Otsu Model: 189

Technical Details
Crew  Four (driver, commander/gunner, loader, hull gunner)
Weight  12 tons (loaded)
Speed  26 km/h
Engine  Mitsubishi A6120VD 6-cylinder air-cooled petrol diesel
Range  170 km
 Type 90 57mm main gun (short barrel) with 100 rounds
Secondary  Two Type 91 6.5mm machine guns mounted in hull and coaxial with 2,745 rounds
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