R-31 (Russian: Р-31; NATO reporting name: SS-N-17 Snipe; bilateral arms control designation: RSM-45) was a Soviet submarine-launched ballistic missile.
A first test flight took place from the Yankee II Class submarine K-140 (photo) in December 1976.
It was a two-stage delivery device armed with a single 500 kt nuclear warhead.
A particular practical benefit of the design was the quiet submerged launch system, which used the missile's own buoyancy to lift it to the surface.
Apparently this missile was also capable of performing the duties of SLCMs, as the targeting distance could be varied drastically.