Features from several designs were incorporated, including the controllable suspension of the US-German MBT-70 project, the hull of the Leopard 1, and a similar 105mm gun. The design included a rotating cupola for the commander, and a new autoloader for the main gun. Prior to the 1965 decision to design an entirely new tank, some technologies which would later be used in the STB-1 (first prototype) were already in development independently in Japan.The design was finalized in 1964 and various test rigs were built between 1964 and 1967.