The MX Missile

The Peacekeeper nuclear missile, more commonly known by its pre-deployment designation MX (for “Missile Experimental”), provoked a bitter controversy during the Reagan Administration.

MX Peacekeeper MIRV warhead, at the US Air Force Museum in Dayton. Each cone carries a separate nuclear weapon.

Even as the Minuteman III nuclear missile was being deployed in 1970, the Air Force was already interested in a larger version, akin to the Titan II. By taking advantage of better guidance systems, solid-fuel technology and MIRVs (Multiple Independently-targeted Reentry Vehicles, which allowed each nuclear payload to hit its own target), such a missile could be more accurate than the Minuteman, have a longer range, and have the capability to deliver a larger number of independent warheads. From the start, it was intended to be able to hit Soviet missiles in their silos, and was inherently a first-strike “counter-force” weapon. In 1971, the Air Force issued a “request for proposals”, and the project was dubbed “Missile Experimental”, or MX.

The development of the actual missile body was pretty straightforward. MX was to be a solid-fueled three-stage rocket measuring 71 feet tall and almost 8 feet in diameter, with a skin made from epoxy-reinforced kevlar. The lighter skin would allow for a greater range, a bit over 6800 miles, and a larger warhead.

The guidance system was the most sophisticated yet built by the US, and gave the missile incredible accuracy. This was supplemented by an advanced Bus in the warhead (which was considered to be a “post-boost” fourth stage), which had a restartable axial engine and eight attitude-control rockets for changing direction. The MIRV Bus would carry ten new W87 warheads with a 300 kiloton yield. Each of these warheads could each be sent on their own particular trajectory and be delivered within 150 feet of their own target.

The Air Force knew that the Soviets would view the MX as a lethal first-strike threat, and they would therefore consider it one of the highest-priority targets for their own ICBMs, adopting a “use it or lose it” policy of launching several warheads at each MX in hopes of knocking it out before it could be launched. That in turn forced the United States to place a high priority on the survivability of the MX, to enable it to endure a possible pre-emptive Soviet strike and still be able to launch.

The solution proposed by the Air Force was complex. Rather than base the MX in fixed silos like the Titan or Minuteman, they would become the center of a giant elaborate “shell game” called Multiple Protective Shelters (MPS). At each launch site, a series of ten hardened shelters would be constructed along a “racetrack”, but only one missile would be based there. It would be constantly moved by rail car from one shelter to another, and since the Soviets would never know which shelter actually contained the missile, they would be forced to devote a huge amount of resources to hitting all ten of the shelters individually, including all the empty ones.

In addition, the MX was designed for a “cold launch” similar to the system used in submarines, in which the missile was propelled into the air by a steam cylinder before the first stage engines ignited. This prevented damage to the launcher, and allowed for a second missile to be quickly loaded and launched from the same spot.

MX Peacekeeper missile, at USAF Museum in Dayton

By 1981 the missile had passed its test flights and was ready for production, and the Air Force asked for funding to produce 200 missiles (now named “Peacekeeper” but still widely-known as “MX”), and to purchase enough land for the widely-dispersed shelters in Nevada. It came to an eye-popping $37 billion.

The result was a political firestorm. Critics, both civilian and military, argued that the missile was a provocative weapon which destabilized the doctrine of MAD and would fuel yet another round in an endless arms race. Others objected to the astronomical cost. When the Reagan Administration reasoned that the missiles were useful as a “bargaining chip” to negotiate an arms-control treaty with the Russians, detractors pointed to the obvious silliness of spending such a vast fortune on aggressive nuclear weapons only for the express purpose of then banning them and dismantling them. The “logic” of the nuclear arms race had, they concluded, reached a bizarre level of meaninglessness.

In the wake of this public condemnation, the Air Force backed off. Instead of the complicated and expensive “shell game” system, the new Peacekeepers would now be deployed inside a series of hardened silos that would be built at new missile bases. The idea behind this “dense pack” strategy was that the Soviets would not be able to hit all of the MX silos at once or their own incoming warheads would destroy each other, so they would have to strike with one warhead at a time, thereby allowing at least some of the Peacekeepers to survive long enough to launch even under attack.

But this plan too fell under intense criticism as being expensive and impractical. In the end, the Air Force retreated yet again, and finally announced that it would simply deploy the new MX inside the already-existing Minuteman silos, which, since this offered no improved protection for the missiles, promptly raised questions about what the point of the whole project was. These questions became louder when it was revealed that, due to design changes in the warhead, the MX did not have significantly greater range than the Minuteman III that it was replacing.

In the face of budgetary fights, the Air Force was also  compelled to cut the planned number of Peacekeepers from 200 to 100, and then to just 50 (though another 50 missiles were built and used for testing), and it was decided to deploy all of these operational weapons at the FE Warren Air Force Base in Wyoming. Modification of the Minuteman silos there began in 1984 and the first MXs were deployed in 1986. All 50 Peacekeepers were on alert by December 1988.

In 1993 the US and Russia signed a new Strategic Arms Reduction Talks treaty (START II), which slashed the number of missiles on both sides and eliminated MIRVs. By 2005, under the terms of the treaty, all of the MX Peacekeepers had been deactivated and withdrawn from service.

Today, the US Air Force Museum in Dayton OH displays a Peacekeeper missile, its MIRV warhead, and one of the railroad carriers that was designed to shuttle it between shelters.