In 1927, the Osaka Rikugun Zoheisho arsenal began construction of the "#2 light tank" (Type 87). After trials, the Japanese decided that the tank needs more armour and firepower. The design was completed in 1929, and resulted in the medium tank #2589, or "Type 89 I-Go".
The Type 89 had a classic layout: driver's compartment in the front, fighting compartment in the center, engine in the rear of the vehicle. The hull of the I-Go was riveted, and, at least on initial vehicles, was a re-built Vickers MkC hull, also tested by the Japanese at the time. The turret, also riveted, was equipped with a 47 mm, and later 57 mm, gun. The turret was turned manually. The I-Go also had two machine guns, one in the front of the hull, and one in the back of the turret.
The Type 89 had a Daimler gasoline engine. Later vehicles used a domestic Mitsubishi engine. The tank could accelerate to 27 kph, and had a range of 160 km.
The first I-Go tank was built in 1931. The main producer of the tank was the arsenal in the city of Nagoya.
Soon after entering production, the Type 89 received a turret upgrade, with a commander's cupola and rear bay for the machinegun. This variant is known as Type 89A.
In 1935, after experience in Manchuria, the tank was modernized. The tracks were replaced with sturdier ones, with smaller track links, the front hull plate was improved, the observation devices were better protected. The commander's cupola grew in size, and the gun mantlet changed shape. This vehicle was indexed "Type 84B Otsu". The Otsu was mainly produced by Mitsubishi. Type 89A and Type 89B tanks were used by the Army and special landing groups of the Imperial Navy. Production continued until 1937, when they were replaced by the Type 97 Chi-Ha medium tank.
Original article here.