With the ever-closer creep of NATO into territory considered by Moscow to be just temporarily separated from the larger Russian Empire, Putin and company are considering a new generation of mobile missile trains
You see in the old nuclear missile/warhead game, the more survivable nukes you have, the better you off in terms of mutually assured destruction. Hence, silo-based warheads are the most vulnerable, while warheads cruising around the bottom of the ocean somewhere are comparatively safe– provided the bad guys don’t have more hunter killer subs at sea than you have nuke slingers.
That’s what bugs the borscht out of the Russkies. They have silos (that we know where they are due to the Open Skies program). They have a small bomber force (that can only fly from a handful of strips that we watch 24/7). They have a tiny operational SSBN force (that is vastly outnumbered by the advanced 688s, Seawolves, and Virginia class SSNs in the depths whenever they rarely put to sea on a deterrent patrol).
That’s why trains seem like the answer. Russia embraced rail transpo back in the 19th century in a big way and at this point have an amazing 128,000 kilometers of rail line in service. Back in the 1980s, they put some 56 RT-23 Molodets ICBMs (NATO reporting name SS-24 Scalpel) on these rails, constantly on the shuttle around the vast emptiness of Siberia and Soviet Central Asia.

The sole remaining RT-23 in a museum. (Photo: Wiki)
Each one of these trains carried a 79-foot long single missile but it was MIRV’d with 10 warheads, each with a 550–kt yield that was able to hit a city up-to 6800 miles away glow in the dark. A RT-23 on a rail-siding in Kalingrad (what used to be Koingsberg in East Prussia) was capable of soaking all of Europe, most of the Middle East and North Africa, and reach past New York into the U.S. as far as Dallas. An RT-23 on a quiet railway line outside of Vladivostok could reach South as far as Sydney Australia and West over the Pacific as far as San Diego and Las Vegas.
To counter this we came up with the MGM-134 Midgetman, a road-capable scaled down ICBM that never went into production due to the end of the Cold War.

The Midgetman concept, which allowed these hidden nukes to be carried around undisclosed locations in the U.S. Southwest.
However with the great peace breakout and East/West warming in the 1990s, these railway missiles were out out to pasture with the last SS-24 ICBM in Russia being eliminated in April 2008 and a planned replacement, the RT-25, was never built. Today there is but one preserved example, a demilled one in a museum in St.Petersburg.
But that could change if the Russian defense ministry gets its way.
“While the decision to start manufacturing [missile trains] is still pending, the probability is high that it will happen,” the source was quoted as saying, explaining that technical studies and cost estimates are still being conducted.
“In the best-case scenario, they will be deployed by the end of the decade, probably somewhere around 2019,” he said.