The R-27 Zyb was a submarine-launched ballistic missile developed by the Soviet Union and employed by the Soviet Navy from 1968 through 1988. NATO assigned the missile the reporting name SS-N-6 Serb. In the USSR, it was given the GRAU index 4K10. It was a liquid fuel rocket using a hypergolic combination of unsymmetrical dimethylhydrazine (UDMH) as fuel, and nitrogen tetroxide (NTO) as oxidizer. Between 1974 and 1990, 161 missile launches were conducted, with an average success rate of 93%. Total production was 1800 missiles.
The R-27 missiles were deployed on the Yankee I submarines, including the K-219.