JGSDF's main tank M4 became obsolete in the late of 1950's, and difficulty began in that maintenance. The U.S.A. in those days finished manufacturing of M4 already, and was manufacturing M47 and M48.

JGSDF of those days had 2 choice ways. One way importing M47 or M48 from the U.S.A, and another way is complete domestic development.

They determined plainly, It's complete domestic production.

As that reason...JGSDF made much of the transportation by train about tank unit in those days. Therefore their tank's width must be less than 3m. If tank exceeds this width, they have the possibility that an accident occurs in the passage of tunnel and an trains intersection. And that weight is limited in 35t by loading ability of freight train. Because M47's width is 3.52m, it didn't satisfy their request.

In this way, the domestic tank development in Japan restarted after a blank of 10 years from 1945.

The main gun is 90mm caliber 52, It was west world standard in those days. "Nihon Seikou" contracted the development of this gun. They began the gun development of high muzzle velocity and light weight to surpass U.S.A's 90mm gun. "Mitsubishi" contracted the power unit, the hull, other general development.