Development of a new assault gun for the armed forces started at the OKB-40 design bureau of the Mytishchi Machine Building Plant (MMZ), under the supervision of chief designer Nikolaj Aleksandrovich Astrov.
After World War II the Soviet Union took plans, tooling and even several dozen personnel as war reparations to MMZ in Moscow (later transferred to MMVZ and SMZ) and to a factory in Kovrov, and produced copies of the RT 125 as the M1A Moskva and K-125 respectively.