LGM-118 Peacekeeper

• 1. Introduction

  ›

  The LGM-118 Peacekeeper was a weapon designed around a single terrifying question: what happens if the enemy strikes first and nearly wins? Originally called the MX, short for "Missile, Experimental", this intercontinental ballistic missile spent decades in the making, caught between competing strategic theories, Congressional vetoes, and a basing problem that was never truly solved. It could carry up to eleven nuclear warheads on a single rocket, though treaties capped it at ten. Each of those warheads packed a 300-kiloton punch. Yet only 50 of the planned 200 ever entered service. And after less than two decades of active deployment, the entire fleet was deactivated in 2005. How a weapon of such ambition ended so quietly is a story of Cold War politics, scientific ingenuity, and the limits of deterrence logic.

• 2. The Minuteman's Limits

  ›

  Deployment of the Minuteman ICBM began in 1962, and within a few years it had become the main US strategic weapon. But its early versions had a significant limitation: a circular error probable of roughly 0.6 to 0.8 nautical miles and a warhead below one megaton. That combination meant the Minuteman could not reliably destroy hardened Soviet targets like missile silos. It was useful as a deterrent against cities, but not as a counterforce weapon.

  Robert McNamara, the new Secretary of Defense under the Kennedy administration, was tasked with building the most powerful military in the world while simultaneously cutting costs. His solution was to reduce dependence on expensive crewed bombers and lean heavily on missiles instead. By 1964, the United States had more ICBMs than bombers on nuclear alert.

  But the Soviets were improving too. Their missiles had very low accuracy, too imprecise to target US silos directly. However, they were accurate and powerful enough to threaten US bomber bases. A coordinated attack using missiles against airfields and bombers against silo complexes raised the alarming possibility that the US could be left badly exposed. The Air Force concluded it needed a missile that could reliably destroy Soviet silos, not just cities.

  The answer, drawn from advice by the RAND Corporation, was to upgrade the Minuteman II with the NS-17 inertial navigation system. That improvement brought the circular error probable down to 0.34 nautical miles and gave the missile the ability to quickly switch between a pre-set menu of eight targets. The Air Force was adapting, but the changes were still limited by existing technology.

• 3. Golden Arrow and Early Concepts

  ›

  In 1964, the Air Force contracted The Aerospace Corporation to study a wide range of survivable ICBM concepts under a project called "Golden Arrow". The Aerospace Corporation had itself been formed in 1960 by engineers from TRW and other firms with ICBM experience.

  The concepts ranged from the creative to the extraordinary. One proposal called for a turboprop-powered aircraft with enough fuel for two days of continuous flight, carrying up to eight missiles that would be dropped out the rear, parachuted to vertical, and then launched. Another suggested loading missiles and wheeled launchers into existing C-141 Starlifter transport aircraft and dispersing them to airports across the country during crises. The Soviets, theoretically, would need to target thousands of runways, dirt strips, and long stretches of highway to destroy such a fleet.

  Golden Arrow also considered burying missiles in "super hard" silos on the southern faces of mountains. Incoming Soviet warheads, approaching at a shallow angle from the north, would strike the mountainside before reaching the silos. The planners believed that silos capable of surviving a multi-megaton explosion at one mile could be engineered, even if that remained uncertain. The proposed force was 100 missiles across three bases of 30 each, with each missile needing to carry 20 or more warheads to make a viable deterrent.

  To launch such a payload required a new rocket design entirely: the "ICBM-X", with a diameter of 156 inches. That was more than twice the width of the existing Minuteman and larger even than the Titan II heavy design at 120 inches. Alain Enthoven, a senior Pentagon official, framed the budget dilemma plainly: the country's resources, large as they were, could not support a dozen distinct nuclear delivery systems without squandering them all. Golden Arrow was shelved in favor of the Minuteman II.

• 4. SABRE and the Accuracy Breakthrough

  ›

  Since the late 1950s, engineers at the Charles Stark Draper Laboratory had been developing a new kind of inertial navigation platform. Traditional platforms used mechanical gimbals, which could tumble and lose their accuracy in a failure mode called "gimbal lock". The Draper team replaced those gimbals with a sphere floating in a thin layer of fluorocarbon fluid. They called it the "flimbal", apparently short for "floated measurement ball".

  Despite its potential, the flimbal attracted little official support for years. In the late 1960s, Kenneth Fertig managed to secure Air Force funding for a follow-on program called "SABRE", standing for "self-aligning boost and re-entry". The concept was ambitious: a navigation system so precise and mechanically stable that it would not need any external correction during flight, even through the violent shocks of atmospheric re-entry. This was a direct contrast to the stellar-inertial systems being developed by the Navy, which still depended on external reference points.

  For the MX program, Draper developed SABRE into the "Advanced Inertial Reference Sphere", or AIRS. The system would achieve a drift rate of just 1.5 times 10 to the negative fifth degrees per hour. Over the course of a flight, platform drift would account for no more than 1% of the warhead's total positional error. The remaining inaccuracy came from factors like engine firing timing, minor differences in warhead construction, and random atmospheric variation.

  The Air Force also contracted Autonetics for a backup design using mechanical gimbals, the "Advanced Stable Platform". In May 1975, the first hand-built AIRS was transferred from Draper's laboratory to Northrop for further development. AIRS had 19,000 parts, some of which required as many as 11,000 individual testing steps.

• 5. The Basing Problem

  ›

  From the beginning, the hardest challenge facing the MX program was not the missile itself but where to put it. In July 1976, Congress refused to fund a silo-based MX on grounds that fixed silos were too vulnerable. The program was halted.

  President Jimmy Carter reinstated it on the 12th of June 1979 and announced on the 7th of September that 200 missiles would be deployed across eastern Nevada and western Utah. The plan, known as the "Racetrack" proposal, involved placing missiles in multiple protective shelters connected by roads, so they could be moved to confuse an attacker. Local opposition was fierce. Senator Paul Laxalt of Nevada emerged as a powerful critic, and Utah Governor Scott Matheson was also opposed. Even in rural Utah, where initial support had been high, public opinion shifted after the leaders of the Church of Jesus Christ of Latter-day Saints issued a statement of disapproval.

  When Ronald Reagan took office, his close ties to Laxalt proved decisive. Reagan cancelled the shelter system in 1981, calling it "a Rube Goldberg scheme". On the 2nd of October 1981 he proposed using the roughly 60 existing Titan II silos instead, hardened to increase their survivability. He also funded studies of airborne drops from cargo aircraft, an active anti-ballistic missile defense, and burying silos on the south sides of mountains.

  On the 22nd of November 1982, Reagan announced a new approach: "dense pack", or Closely Spaced Basing. Silos would be built to withstand more than 10,000 psi of overpressure, far beyond the 2,000 psi rating of existing silos. The key idea was that silos spaced roughly 1,800 feet apart could protect each other through "fratricide": when an incoming warhead destroyed one silo, the resulting explosion would disable nearby attacking warheads before they reached adjacent silos.

  Critics quickly found the flaw. All an attacker needed was to time several warheads to detonate within milliseconds of each other, and the fratricide effect would be neutralized. Such precise timing was achievable by launching multiple warheads from a single missile. Congress rejected dense pack as well.

• 6. Scowcroft, Compromise, and Deployment

  ›

  Reagan responded to the dense pack rejection by appointing Lieutenant General Brent Scowcroft to chair a Commission on Strategic Forces. The Scowcroft Commission delivered its report on the 6th of April 1983, with a finding that surprised many: the "window of vulnerability" feared by the Air Force, the scenario in which the Soviets could disarm the US ICBM fleet in a first strike, had never actually existed. The commission's review of attack scenarios found that none of them could meaningfully blunt a US response or limit its options.

  The report recommended deploying 100 MX in existing Minuteman silos as what it called a "demonstration of national will". On the 10th of August, the Secretary of Defense ordered 100 Peacekeepers to be deployed at Warren AFB in Wyoming. A parallel effort began on the MGM-134 Midgetman, a small, single-warhead mobile missile deliberately designed so that destroying one would cost an attacker an entire warhead for each one they eliminated.

  For the Peacekeeper itself, the first test flight took place on the 17th of June 1983, launched by the Air Force Systems Command Ballistic Missile Office at Norton AFB in California, along with the 6595th Missile Test Group at Vandenberg AFB and Martin Marietta. Fired from Vandenberg's Test Pad-01, the missile traveled 4,200 nautical miles and struck successfully in the Kwajalein Test Range in the Pacific. A total of 50 flight tests were accomplished. The operational missile was first manufactured in February 1984.

  Despite the plan for 100 missiles, Congress limited the deployment to 50 in July 1985, citing the lack of a survivable basing solution. Even then, the AIRS guidance system was not ready when the missiles were deployed to the 90th Strategic Missile Wing at Francis E. Warren Air Force Base in Cheyenne, Wyoming, in December 1986. When 60 Minutes and the Los Angeles Times published allegations about the procurement chaos surrounding AIRS, including claims that replacement parts had been sourced from Radio Shack and that managers had created fictitious shell companies to obtain test equipment, the Air Force confirmed that 11 of the 29 missiles then deployed were not operational. Northrop was fined $130 million for late delivery, and whistleblower lawsuits followed. The complete AIRS supply for the first 50 missiles was not finished until December 1988.

• 7. Retirement

  ›

  The Peacekeeper program had cost around $20 billion by 1998, producing 114 missiles at roughly $400 million per operational missile. The flyaway cost of each warhead was estimated at between 20 and 70 million dollars.

  By the time the system reached full deployment, the strategic landscape had already shifted. The United States and the Soviet Union were negotiating the START II treaty, which would limit each ICBM to a single warhead. A Minuteman could deliver one warhead far more cheaply than a Peacekeeper. The Peacekeeper's multi-warhead advantage, the very capability that had driven decades of development, became the reason for its removal. The United States agreed to withdraw it from service under the treaty's terms.

  Retirement proceeded gradually. Seventeen missiles were withdrawn in 2003, leaving 29 on alert at the start of 2004 and only 10 by early 2005. The last Peacekeeper was removed from alert on the 19th of September 2005 during a ceremony at which the 400th Missile Squadron was formally inactivated. An Under Secretary of the Air Force, speaking at the ceremony, credited the Peacekeeper with helping to end the Cold War.

  The weapon's hardware found a second life. The W87 warheads were transferred to the Minuteman III, the very missile the Peacekeeper had been designed to supplement. The Peacekeeper rocket stages were converted by Orbital Sciences Corporation into the Minotaur IV, a four-stage civilian satellite launcher. Seven Minotaur IV flights had been made using components from the old missile fleet. A rail garrison box car, a remnant of the cancelled mobile deployment system, went on display at the National Museum of the United States Air Force.