The LGM-118 Peacekeeper, originally known as the M-X for “Missile-Experimental” (a.k.a. “MX”), was a MIRV-capable ICBM produced and deployed by the U.S. from 1985 to 2005. The missile could carry up to 12 Mk21 RVs but it was treaty-limited to just 10, each armed with a W87 nuclear warhead. Initially, plans called for deployment of 200 of these missiles, but basing and budgetary concerns resulted in only 50 entering service. Studies on the underlying concept started in the 1960s. The idea was to allow the U.S. to absorb a sneak attack by the USSR with enough warheads surviving to attack the remaining Soviet missile fleet. To do so, the missiles had to be highly accurate, be based in such a way that enough would survive to launch a counterstrike, carry a large number of warheads so the survivors would still inflict massive damage, and be able to rapidly re-target so they could be aimed at only those missiles the Soviets had not yet fired. Ultimately the only problem that was never completely solved was the issue of basing. Initial development began in 1971, with full-scale development starting in 1974. In July 1976, Congress refused to fund MX using a silo-based system on grounds of vulnerability, and the project was halted. Several new proposals were made for alternate basing arrangements, but none could be agreed upon. Meanwhile, development of the missile, itself, plodded along. President Carter ordered initial production in 1979 but was overturned by Congress. When President Reagan took office, he proposed deploying an initial force of the new missiles in the approximately 50 existing Titan II silos, removing those outdated missiles with their toxic propellants from service. The silos would be modified for much greater strength, and a number of Minuteman III silos, similarly adapted over time, would bring the force to a total of 100 missiles. Other basing options were also suggested and explored. For example, on 22 November 1982, Reagan announced that the system would be deployed in new silos in what was then known as “Closely Spaced Basing” (later called “dense pack” and derisively by others, “dunce pack”). This speech is mentioned here because it was during this speech that Reagan made the first mention of the name Peacekeeper. Actually, the post-MX name was planned to be “Peacemaker,” but at the last minute was officially changed to Peacekeeper. The missile was first test fired on 17 June 1983 from an above-ground canister on Test Pad-01 at Vandenberg AFB. The next seven launches were also from the canister, but all remaining test flights were from silos at the base. In July 1985, Congress canceled the 100-missile option and limited the deployment of Peacekeeper ICBMs to 50 missiles until a more “survivable” basing plan could be developed. The 400 SMS, based at Francis E. Warren AFB, WY, was the Minuteman squadron chosen for conversion to Peacekeeper, and IOC was attained in 1986. Meanwhile, development of the rail-garrison system for the other 50 missiles was carried out in parallel. However, budgetary constraints and the collapse of the USSR just a few years later led to the rail-garrison scheme being scrapped. In the end, just 50 Peacekeeper missiles were deployed in converted Minuteman silos. Disarmament treaties signed after the Peacekeeper’s deployment resulted in those missiles being gradually retired, with 17 withdrawn during 2003, leaving 29 missiles on alert at the beginning of 2004, and only 10 by the beginning of 2005. The last Peacekeeper was removed from alert on 19 September 2005, and then the 400 MS was inactivated as well. During the inactivation ceremony, an Under-Secretary of the Air Force credited the Peacekeeper with helping to end the Cold War. Many of the Peacekeeper’s state-of-the-art warheads and RVs are now deployed on Minuteman III missiles.