R-27 (ballistic missile)

The R-27 (Russian: Р-27) 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.

The missile's body is an all-welded construction made of hard-worked AMg6 (АМг6) aluminium-magnesium-alloy panels, which underwent a two-step process of deep industrial etching and mechanical milling, reducing the plate thickness to one-fifth and one-ninth of the thickness of the original plate.

The outer surface of the missile was covered with a protective heat- and moisture-resistant Asbestos-based coating. In order to fit the R-27 into the corresponding launch tube, the missile was built without fins, but instead has several rows of rubber shock absorbers to keep the missile's skin from scratching along the side of the launch tube when fired.

The missile's tip featured a single, 650-kg detachable warhead with a yield of 1 MT. A high-explosive linear-shaped charge was used to separate the warhead from the missile.

Directly beneath the warhead, the instrumentation necessary for guidance of the missile was housed inside of a hemispherical compartment formed by the upper bulkhead of the oxidiser tank. This design decision allowed the easy removal of the guidance system from the missile for maintenance and removed the need for a service hatch.

To maximize the volume of propellant available inside the missile, the upper oxidiser tank and the lower fuel tank shared one common bulkhead instead of one bulkhead each as it was absolutely necessary to use every bit of volume available to be able to fit the missile into a submarine.

Another novelty was factory fueling with the subsequent "ampulization" of the tanks by welding filling and drain valves. In conjunction with efforts to improve the corrosion resistance of materials as well as the tightness of seams and joints, these fabrication methods allowed the missile to have a lifetime of 5 years, which was later extended to 15 years.