The SS-20 (NATO designation: Saber) is an intermediate-range, solid fuel, two-stage ballistic missile designed to carry a nuclear payload. The two stages of the RSD-10/Pioneer missile were descended from the SS-16 ICBM.
Deployed by the USSR beginning 1976 at 48 bases on its borders, aimed at targets in Western Europe and Asia, it had a range of 4,400 km (2,700 miles). Its primary configuration, Mod-2, carried a MIRV with three 150-kiloton warheads. The lesser-used Mod-1 carried a single 1-megaton warhead, while the Mod-3 (SS-X-28) model carried 1 or 3 warheads of variable size. The targeting system was deemed accurate to within half a kilometer.
The SS-20 was meant to be fired from a mobile launcher, basically a large semi truck trailer which carried all the targeting and support equipment needed. The solid-fuel rockets meant only minimal maintenance was needed before the missile was ready for launch.
The SS-20 was outlawed by the 1987 Intermediate-Range Nuclear Forces (INF) treaty, and over 650 missiles and 450 launchers have been destroyed. The main missile production facility in Votkinsk (Votkinsky Zavod), which also manufactures the SS-23 and SS-25, is monitored by an American inspection team to guarantee compliance.
Data taken from http://www.fas.org/nuke/guide/russia/theater/rt-21m.htm, www.nasm.edu, and the Votkinsk Machine Plant page at http://topol.ru/missiles.html.