The Russian navy has just completed two successful tests of the R-29RM SLBM (sea launched ballistic missile). The 40 ton R-29RM, or Sineva, is the last liquid fuel Russian SLBM in service. Liquid fuel missiles are more complex than solid fuel missiles, even though they use fuel that can be stored for long periods inside the missile. Russia continued to use liquid fuel SLBMs for so long because large solid fuel rocket motors are actually large, carefully shaped, blocks of slow burning explosives. These motors are very difficult to make, and it was only near the end of the Cold War that Russia finally mastered the technique.
The R-29RM is an update of the original 36 ton R-29R, which entered service in 1986. The R-29RM entered service two years ago, and has proven very reliable. The R-29RM has a range of 8,300 kilometers (300 more than the R-29R) and a payload of 2.8 tons (compared to 1.65 tons for the R-29R).
Russia's only solid fuel SLBM in service is the R-39, which can only be carried by the huge Typhoon class SSBNs. The 90 ton R-30 entered service in 1983. It has a range of 8,400 kilometers and a payload of 2.2 tons. The R-39 was too large for the new, Borei class of SSBNs, and efforts to design a smaller SLBM failed (for financial, as well as technical, reasons), and a successful solid fuel ICBM, Topol-M, has been adapted as a SLBM instead. This missile, the Bulava, has had a lot of developmental problems, and suggestions that the R-29RM be used instead, were ignored.