By the middle of this century, a large chunk of the United States’ nuclear arsenal could be located on a doomsday subway system, where unmanned cars move back and forth on a single track, prepared to launch at a moment’s notice.

Or a least that’s one of several ideas that the Air Force is potentially mulling over as it prepares to replace its decades’ old intercontinental ballistic missiles (ICBMs). To jumpstart those preparations, the Air Force earlier this month released an open call for proposals that would help the Air Force decide what the future land-based nuclear force would look like for the 50-year period starting in 2025.

At stake is a part of the nation’s rapidly aging nuclear arsenal, which consists of the "triad" of land-based ICBMs, submarine-launched missiles, and bombers armed with nuclear weapons.

Supporters of this deterrent argue that, despite the end of the Cold War, it is still needed to deter a potential enemy from threatening the United States with nuclear weapons, or even other weapons of mass destruction. “The official reason is still one of flexibility, and survivability in the event of a nuclear attack,” says Ivan Oelrich, a long-time defense analyst and expert on nuclear issues. “The real unspoken argument is bureaucratic inertia.”

In recent years, some US Pentagon officials have questioned whether keeping all three elements of this costly triad is really needed, though no changes have yet been made. In the meantime, parts of the system are rapidly approaching their use by date. The current ICBM, the Minuteman III, is expected to reach the end of its life by 2030.

Of the five different ideas the Air Force is currently exploring, the underground tunnel concept would be one of the more dramatic changes from the current system, which has missiles located in fixed, underground silos spread out across three bases. The tunnels would in theory allow the missile to survive direct nuclear attacks, since an enemy wouldn’t know precisely where the missile is located at any given time.

“The tunnel concept mode operates similar to a subway system but with only a single transporter/launcher and missile dedicated to a given tunnel,” the Air Force says. “The vehicle moves at random down the length of the tunnel.”

That, however, is not the only possible new system. Another concept involves putting the missiles above ground, perhaps on specialised vehicles called “transporter erector launchers.” Those vehicles may have to venture on to public roads or lands, according to the Air Force, or even travel off road.

‘Fancy ideas’

While the idea of off-road vehicles and underground trains transporting nukes may sound wild, the Air Force says it’s also considering more basic options, such as simply keeping the current Minuteman III through until 2075, or undertaking modifications to the system. Yet another option would be building a new missile that would replace the Minuteman, but still use underground silos.

None of these proposals are right around the corner, cautions retired Lt. Gen. Frank Klotz, who last served as the commander of Air Force Global Strike Command, which is responsible for the US ICBMs, as well as nuclear-armed bombers. “The purpose of sending out the request for concepts is to flesh out the ideas in greater detail so that at some point, they can be subjected to intense analysis as to the cost, feasibility, and operational effectiveness,” says Klotz, who is now a senior fellow at the Council for Foreign Relations.

While any such proposal for underground tunnels or mobile ICBMs is likely far off in the future, he says that such options are not necessarily more expensive in the long run, since it would allow the Air Force to consolidate its operations. When the Minuteman missile was first deployed some 50 years ago, the concept was to disperse them to reduce their vulnerability to a Soviet attack. But maintaining and protecting missiles over such a large area, such as paying for vehicle fuel, can be burdensome.

Today, missile fields are spread out across three bases: the smallest, at Minot Air Force Base in North Dakota, covers some 22,000 sq km (8,500 sq mi). “That’s roughly the size of the state of New Jersey,” Klotz says.

Arms control experts agree that a mobile ICBM force is probably not around the corner. The recent Air Force announcement “is a preliminary first step to explore theoretical options for replacement of the Minuteman III ICBM force,” says Daryl Kimball, executive director of the Washington DC-based Arms Control Association.

Kimball points out that the US has cut its nuclear arsenal in recent years - there are currently just 420 Minuteman IIIs, and to invest now in an entirely new system makes little sense. “The reality is that the current plans for modernising the strategic triad, which were developed years ago, is too costly given the current budget environment,” he says.

The idea of putting a nuclear weapon on a moving vehicle is also too risky, according to Hans Kristensen, director of the Nuclear Information Project at the Federation of American Scientists. “This notion of rolling around on country roads and rural areas, with an increased risk of accidents, seems to be a step back in this day and age,” he says.

But this is not the first time the Air Force has looked at mobile ICBMs, Kristensen notes. In the 1980s, the government debated putting the Peacekeeper missile on trains, or even “race tracks.”

“At the end of the day, all these options were way too expensive and they ended up in silos,” he says. “You can come up with fancy ideas, but the reality check at the end of the day is: what is needed, what is necessary, and how much can we afford?”

The mostly like outcome is that the United States will simply keep the Minuteman III, and refurbish it as it has done before. It just finished a multi-billion dollar refit, which involved updating everything from fuel to guidance parts, and the end result is a nearly “new” missile.

Repeating that refurbishment to keep the Minuteman III going until 2075 is the most likely path for the Air Force, according to Kristensen. “Mobile and tunnel systems, that’s a pie in the sky,” he says.

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