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The Peacekeeper (MX) ICBM


Last updated 10 October 1997

The Peacekeeper (still better known by its pre-deployment designation "MX" for missile-experimental) is the largest and newest ICBM in the U.S. arsenal today. It is expected to be retired by the end of 2004 under the terms of the START II treaty, signed 3 January 1993. Since this treaty has not yet been ratified by the Russian Duma though, the Peacekeeper retirement is still not assured.

Specifications and Performance
Weight195,000 lbs (88,450 kg)
Length70 ft 10 in (21.6 m)
Diameter92 in (2.34 m)
RangeOver 6830 mi. (over 11,000 km); 6000 mi (9600 km) [Janes]
Speed15,000 miles/hour (24,000 km/hr; 6.7 km/sec)
CeilingAbout 500 miles (805 km)
Throw Weight8710 lb (3950 kg);
PBV weight 3010 lb (1365 kg);
Net warhead load 4700 lb (2585 kg)
Accuracy (CEP)330ft (100 m)
First Stage 500,000 lb (2,200,000 KN) thrust Thiokol solid fuel motor;
Weight 49,000 kg
Second Stage Aerojet General solid fuel motor;
Weight 27,000 kg
Third Stage Hercules solid fuel motor;
Weight 7,700 kg
Post-Boost Stage Rocketdyne restartable liquid fuel motor; storable hypergolic fuel

The solid fuel motors were wrapped with Kevlar fiber to create strong light weight casings. Second and third stages use extendable exit cones.


Gimballess AIRS (advanced inertial reference sphere) inertial guidance system manufactured initially by Northrop and later by Autonetics Division, Rockwell International. Post boost vehicle (PBV) or bus has an axial engine and eight attitude control nozzles.

Go to AIRS page


50 missiles each with ten 300 Kt W-87 warhead/MK-21 RVs. All are deployed at F. E. Warren AFB, Wyoming. By adding enriched uranium rings to the thermonuclear secondary stage, the W-87 can be upgraded to 475 Kt, though there are no known plans to do so.

The W-87 was selected over three other options: the W78 used on the Minuteman III, and two higher yield warheads -- the 500-600 Kt CALMENDRO warhead (developed at LANL but transferred to LLNL), and the 800 Kt MUNSTER. The W-87 is more efficient than the W-78, using less fissile material for a similar yield.

The Mk-21 RV (formerly known as the ABRV - advanced ballistic re-entry vehicle) was selected over the Mk-12a RV due to its greater accuracy, greater hardness (to weapon effects), lower cost, at the penalty of greater weight. The joint selection of W-87/Mk-21 was made by the DOD on 29 January 1982. The PBV can accomodate 12 Mk-12a RVs or 11 Mk-21 RVs.



Deployed in former Minuteman misisle silos with hardeness of circa 2200 psi.

The Peacekeeper was the first (and only) U.S. "cold launched" ICBM. Instead of igniting the main engine immediately in the silo for lift off, a thermochemical gas generator creates pressure to eject the missile from its launch tube. The main engine ignites after it as left the launch tube and is 150 feet in the air. This was originall attractive for launching from mobile transporters, but it allows the rapid reloading a reuse of silos for multiple launches. Cold launch is used on all U.S. submarine missiles, and the Soviet SS-17, 18, 24, and 25.

Development History

In the early 1960s the U.S. deployed the largest ballistic missile it ever developed, the liquid-fueled Titan II (which first went on combat alert in April 1963). Even while this missile was being deployed, the Air Force had initiated a study of another large ICBM, issuing an operation requirement for on 23 October 1963. There was considerable interest in applying the solid fuel missile technology in use on the Minuteman program for another large missile that would still retain the capability of being mobile. These early efforts did not culminate in an actual missile development program. It was not until Required Operational Capability report 16-71 (ROC 16-71) was issued on 2 November 1971 that the actual development of MX (Peacekeeper) was initiated, starting in February 1972. On 4 April 1972 the Air Force designated the new missile ICBM Missile-X or "MX", a name it was destined to retain in popular usage.

From the outset this missile was intended to be a counter-force hard target weapon -- a missile silo killer with inherent first strike capability. The MX was developed to improve "survivability, range, accuracy, payload, and target flexibility". Greater accuracy and payload made it an economical silo killer; survivability was to be enhanced by making it mobile.

The development program for the missile proceded very rapidly. The inertial guidance system adopted for the missile (the AIRS) had already been under developemnt for several years, and solid fuel engine technology had reached a high state of development.Between January and March 1976 the program transitioned from conceptual development to test component fabrication. By late 1981 all four stages had been successfully tested on the ground.

Initially air and ground mobile options were considered, but the basing mode for MX remained a difficult and controversial issue that in the end was never adequately resolved. The central problem was that the missile had so many warheads (ten each), and was so inherently threatening (being highly accurate it raised fears of a silo-killing first strike) that it was a very attractive high value target. The Soviet Union could justify targeting up to 10 of its own warheads against each missile. It was very difficult to come up with a basing mode that could plausibly survive such a concentrated nuclear onslaught.

From a technical and financial perspective the best option was the one intially chosen for MX deployment, the MPS (Multiple Protective Shelter) system. This approach esentially created 23 so soft silos for each MX missile distributed along a huge "racetrack". The missile would be shuttled from shelter to shelter randomly so that the Soviet Union would never know where it was. The shelters were hard enough and far enough apart that only one could be destroyed by each Soviet warhead. Although this basing scheme was extravagantly expensive ($37 billion) it was the cheapest alternative of the ones that were likely to work. However it was doomed by the enormous demand for land by the originally planned 200 missiles, whch created strenuous public opposition.

On 22 November 1982 the administration proposed the Dense Pack scheme (and also changed the MX's name to "Peacekeeper"). This involved building superhard silos (>10,000 psi hardness) only 1800 feet apart, the idea being that "fratricide" among a wave of attacking warheads (the tendency of nearby nuclear explosions to damage other warheads) would allow a substantial portion of the force to survive, which could then be launched before the next wave arrived. This scheme suffered from certain questionable assumptions and the possibility of Soviet technical improvements that could totally defeat it (like using terminally guided warheads).

In the end, the great basing mode saga wound down with the Reagan administration proposing that the MX simply be emplaced in existing Minuteman silos in April 1983. The only other option available was simply to kill the program outright. The MX was now well into flight testing, and the program had enough momentum that immediate termination was not in the cards. Congress quickly approved the silo basing option. Because of this extremely vulnerable basing decision, the MX program ultimately failed to achieve its survivability objectives.

Construction began at F.E. Warren in 1984 to accomodate the Peacekeeper in the Minuteman silos. The first four missiles were delivered to Straetgic Air Command in October 1986. Initial operating capability was achieved in December. During the first two years of deployment the AIRS proved to be a major problem. Despite years of work, by July 1987 Northrop Electronics Division had succeeded in delivering only a small number of usable INS units. Up to one-third of the silo-emplaced force had no guidance system. In January 1988 20 missiles were finally operations, and by December 1988 all 50 MX missiles (with guidance systems) had been deployed.

Due to the decision to use the more accurate, cheaper, but heavier Mk-21 RV over the Mk-12a, the range of the Peacekeeper was reduced below that originally planned. Problems wth SALT II weight restrictions required removing some missile propellant, further reducing range. The Peacekeeper, as deployed, thus failed to achieve the programs range objectives and was unable to reach the southernmost Soviet ICBM fields (just like the Minuteman III/Mk-78 system). This could have been corrected easily by simply removing one of two warheads however.

Under the terms of START II (signed 3 January 1993, but not yet in force due to the failure of the Russian Duma to ratify it) the Peacekeeper missile must be retired by 2004. Current plans are to switch the 500 W-87/Mk-21 warhead/RVs to the Minuteman III.

The cost of procuring a Peacekeeper missile (the "flyaway" cost) was only about $20 million (FY 82). The total cost of the program was approximately $20 billion however, at a pro-rated cost of $400 million per operational missile, or $40 million per deployed warhead. A total of 114 Peacekeepr missiles were produced (due to the need for test missiles and spares).