By April 1928, the new light tank design was finished. The prototype of the was completed in 1929 and designated as the Type 89. Later, the Type 89 was re-classified as a "medium tank" because the weight increased to over 10 tons due to several improvements. As the army's Sagami Arsenal lacked the capacity for mass production, a contract was awarded to Mitsubishi Heavy Industries, which built a new tank factory to specifically produce this model. Production of the Type 89 began in 1931 and it soon became the main battle tank of the Japanese Army.