This week Russia announced a strange-sounding plan to load nuclear-tipped intercontinental ballistic missiles onto trains with specially-designed boxcars that could launch these ICBMs right from the track. The Russians call it the Combat Railway Missile Complex and say it will be active in 2018.

The idea may sound ludicrous, but it's strategically sound—at least in theory. Instead of keeping the ICBMs in underground silos on constant alert, Russia could roll them out during a crisis. That way, no one can surprise you with a nuclear strike that incinerates your missiles on the ground and takes away your ability to respond. Nuclear deterrence depends on the guarantee of mutually assured destruction. Trainloads of nuclear missiles, randomly dispersed from a deep mountain base, are supposed to provide that security.

However, a moving target isn't necessarily a safe target, and satellite imaging advances may make this idea unsound. "Mobile systems that depend on roads or rail lines visible via overhead imagery effectively shrink the target area and could significantly lower the number of missiles required to barrage mobile systems," according to a 2014 Rand study. In other words, clever targeting professionals could identify where the nukes are stowed, calculate where they'd be from the speed of the trains, and bombard everywhere along the rail lines that they might be.

The nuke rail idea isn't a new one. The idea is similar to one proposed by the United States Air Force in 1986 as a possible way to launch Peacekeeper ICBMs. In the proposed American system, 25 trains would be equipped with two missiles each. The launch cars would elevate to fire. Another train car would contain fuel, another would store maintenance equipment, and another would be dedicated to housing a heavily armed security team. The launchers would be kept in hardened alert shelters; during an alert, the trains would roll out over the rail network.

The final design was completed in 1990 after four years of work, but the project was cancelled in 1991. But here's an intriguing thought: America's Minuteman III missiles currently on alert are kept in launch facilities from the 1970s that are wearing out. The Air Force needs to design a replacement—a new way to keep ICBMs on alert. Could rail be the answer for the United States as well?

Probably not. Russia (still the only nation that could launch enough nuclear warheads far enough to take out the United States' arsenal) has satellites and could do the same a strike calculations needed to strike nuke-carrying trains. Besides, the U.S. rail system, clogged with merchandise and in lousy shape, is not as robust as needed for this plan to work within a reasonable cost. According to the 2014 RAND report, the price tag for a rail garrison mobile launch system would be $30 billion.

Even if the Russian plan is ultimately impractical, the fact that Russia is modernizing and adapting its nuclear posture is troubling, considering the mounting tensions between the two nations. Russian President Vladimir Putin on Friday signed into law a new defense doctrine that identifies NATO as the chief threat to Russian security and claims the right to use nuclear weapons to counter any aggression that "threatens the very existence" of Russia. The nukes-on-a-train announcement is one aimed at the United States, and another sign that the new cold war is steadily getting frostier.

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