Over the next six years, Russia will replace most of its Cold War era ICBMs with the new RS-24. This is an improved version of the Topol-M (the RS-12M). The solid-fuel RS-24 entered service earlier this year, and will be the only ICBM built in the near future. The RS-24 is slightly heavier version of the 46 ton Topol-M, and can carry six warheads, versus one on the RS-12M . The RS-24 will be deployed in silos as well as on wheeled vehicles. The Russians developed the RS-24, in part, for the larger warhead capacity (essential to penetrate American missile defenses.)
There are over 70 RS-12/24 missiles in service, most of them fired from silos. About 15 are the road-mobile RS-24s, that avoid destruction in a first strike, by constantly moving around on the roads 200-300 kilometers northeast of Moscow. The 17.4 meter (54 foot) long transporter for these 46 ton missiles is a 16 wheel vehicle, using a 710 horsepower diesel engine. Russia continues to make component and design improvements to its most modern ICBM, the RS-12/24. This has increased its service life from ten to 21 years.
This is all part of a program to replace Cold War era RS-18 (SS-19) and RS-20 (SS-18) ICBMs with the the newer Topols, more rapidly than earlier planned. This is the result of more money being allocated to buying ICBMs, and more reliable new ICBMs becoming available. Even so, Russia is not producing enough Topol Ms each year to replace the older liquid fuel missiles before they reach the end of their planned service life. So these older missiles are being refurbished, to extend their time in service until enough RS-24s can be built.
Meanwhile, Russia continues to test launch older RS-18 and RS-20 ICBMs. Russia still has over a hundred (out of a 1980s peak of 360) RS-18s in service, and expects to keep some of them active into the next decade. The test firings for the last four years have been successful, and other quality-control tests have come back positive. The 106 ton, 24.5 meter/76 foot long RS-18 uses storable liquid fuel, meaning that the missile is inherently more complex than a solid fuel missile.
The U.S. introduced solid fuel rockets for ICBMs in the early 1960s, but it took Russia two more decades to master this technology. Meanwhile, the RS-18 entered service in 1975, and it wasn't until the 1980s that Russia began producing reliable solid fuel rocket motors, large enough for ICBMs (the 45 ton RS-12). Throughout the 1990s, Russia continued to refine the RS-12 design, going from the original Topol, to the Topol M and now the RS-24. This mirrors the U.S. Minuteman I, which appeared in the 1960s, but was constantly upgraded since then, and now is the sole U.S. ICBM in service as the Minuteman III.
The last RS-18s were manufactured in 1990, and Russia expects each of them to have a useful life of 30 years via the same kind of product improvements being applied to the Topol M. Annual test launches ensure reliability. The RS-18 was developed as a "light" ICBM, in effect, a competitor for the U.S. Minuteman series. The RS-18 was the first Russian ICBM to carry MIRV (Multiple, Independent Reentry Vehicles). That means each warhead had its own guidance system. The RS-18 carries six warheads, and has a range of 10,000 kilometers, compared to the RS-12/24's 11,000 kilometers. Russia is also extending the life of its heavier (217 ton) RS-20 ICBMs to 30 years. This missile carries ten warheads, and is also being converted to launch satellites.