The R-39 is a Russian submarine launched ballistic missile. It has the NATO reporting name of SS-N-20 Sturgeon and the bilateral designation RSM-52.

The R-39 is a intercontinental missile, it has a three stage solid-fuel (ammonium perchlorate) boost design with a liquid-fuel post-boost unit carrying up to ten MIRV warheads. Like other SLBMs the initial launch is powered by a gas generator in the bottom of the firing tube, during the missile's passage through the water additional motors produce a gaseous wall around the missile, reducing hydrodynamic resistance. The launch system is designated D-19.

Development work began at NII Mashinostroyeniya in 1971 and the design gained official approval in 1973. Initial test flights from 1979 found problems in the solid-fuel boost engines, over half of the early flights failed. Later tests aboard a modified Typhoon class submarine were more successful and deployment began in May 1983, with 20 missiles in each submarine. Work on an improved version began immediately and was deployed from 1989. As of April 2003 100 missiles were deployed with 1000 warheads and a total throw-weight of 255 Mt.

Under the terms of the Start I and Start II treaties, from 1996 a number of R-39 missiles were destroyed, 20 in total to 2003.

A successor design, the R-29RM (SS-N-23 Skiff), was developed from the late 1980s and began testing in 1996, financial issues, development problems and early test failures seriously delayed the program. But by 2003 96 missiles of this type had been completed.