R-21 (missile)

The R-21, known to Western intelligence as the SS-N-5 Serb, was a single-stage, storable liquid-propelled submarine-launched ballistic missile. Its D-4 launch system used a wet launch technique, in which the missile tube was flooded with water before the weapon was fired from a submerged submarine. It was intended to replace the earlier D-2 launch system and was carried aboard Golf-II class diesel-electric boats and Hotel-II class nuclear boats. Western estimates credited it with a roughly 2,800-pound reentry vehicle carrying a warhead of 2.0 to 3.5 megatons over a maximum range of about 700 nautical miles, guided by an inertial system. Development began in the late 1950s, was authorized in March 1958 and passed through dummy launch trials in the Black Sea before successful submarine firings in 1960. Deployment on Golf and Hotel submarines began on 15 May 1963, and the missile stayed in operational service until 1989, with 193 of 228 launches successful. The earlier K1.1 test missile paraded in Moscow was mistaken in the West for the SS-N-5.