The MR-UR-100 Sotka was a MIRV intercontinental ballistic missile (ICBM) deployed by the Soviet Union from 1978 to 1993. The more advanced MR-UR-100UTTh version began development in 1979. The new missiles had completely replaced the original version by 1983, at which time the Soviets fielded 270 launchers. From there the number of launchers declined, and by the 1991 START I Treaty they were down to 76. All were scheduled for dismantling and removed from the inventory.