LGM-118 Peacekeeper
The LGM-118 Peacekeeper, originally known as the MX for "Missile, Experimental", was a MIRV-capable intercontinental ballistic missile produced and deployed by the United States from 1986 to 2005. The missile could carry up to eleven Mark 21 reentry vehicles, each armed with a 300-kiloton W87 warhead. Plans called for building and deploying up to 200 MX ICBMs, but budgetary and political concerns limited the final procurement; only 50 entered service. Disarmament treaties signed after the Peacekeeper's development led to its withdrawal from service in 2005.
Studies on the underlying concept started in the 1960s. The idea was to allow the US to absorb a sneak attack by the USSR with enough warheads surviving to attack the remaining Soviet missile silos. To do so, the missiles had to be highly accurate, be based in such a way that enough would survive a nuclear attack, 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. Over its development through the 1970s, MX emerged as a highly accurate, rapid-firing, and quickly retargeted system. 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. President Jimmy Carter ordered initial production in 1979 but was overturned by Congress. After considerable debate about the system, in October 1982, President Ronald Reagan announced that 50 of the newly named Peacekeepers would be put into service in existing LGM-30 Minuteman silos, a temporary measure until final basing was decided. The first flight test took place in 1983, which included the successful launch of six inert re-entry vehicles, each hitting pre-planned targets. It was the first US ICBM to use a cold launch system.
Peacekeeper reached initial operational capability in 1986. At this time, the United States and the Soviet Union were negotiating the START II treaty, under which ICBMs were allowed to carry only a single warhead each. Because the Minuteman could carry a single warhead for far less money, the United States agreed to remove the Peacekeeper from their nuclear force in this treaty. Despite the US withdrawal from the Anti-Ballistic Missile Treaty and the subsequent Russian withdrawal from the START II on 14 June 2002, the last Peacekeeper missile was deactivated on 19 September 2005. Their advanced W87 warheads were moved to the Minuteman III.
The private launch firm Orbital Sciences Corporation has developed the Minotaur IV, a four-stage civilian expendable launch system using old Peacekeeper components., seven Minotaur IV flights have been made.
Development and deployment
Minuteman
Deployment of the Minuteman ICBM began in 1962, during the Cold War, and proceeded rapidly. Limited accuracy with a circular error probable of about and a small warhead of less than 1 megaton meant the system was unable to attack hardened targets like missile silos. This limited these early models to attacks on strategic targets like cities and ports, and the system had little or no capability as a counterforce weapon. The Air Force relied on its crewed bombers as the primary weapon for attacking hardened targets and saw the ICBM as a survivable deterrent that would guard against an attack on its bomber fleet.Soviet missiles were known to have very low accuracy, far too low to directly attack US missile silos. They did have the combination of accuracy and power to attack the US bomber bases. Although it would be very difficult to arrange, there was the possibility that a combination of missile attacks on US bomber bases combined with bomber attacks on the missile bases would leave the US at a disadvantage. The survivability of the missile fleet became increasingly important, especially after the Kennedy administration took power, and the new Secretary of Defense, Robert McNamara, was given the task of making the US military the most powerful in the world while at the same time reducing its expenditures. He solved this problem by greatly reducing reliance on bombers, and by 1964, there were more US ICBMs than bombers on nuclear alert.
By the mid-1960s, the missile had become the main US strategic weapon. This led to concerns about various warfighting scenarios, especially as the Soviets improved their missiles. In the event of a Soviet missile launch, the US faced the difficult decision of whether to fire their missiles immediately or wait to determine the targets of the Soviet missiles. Firing early might mean striking civilian targets when the Soviets had only targeted military installations, something US politicians considered to be a serious problem. Even if the Soviets attacked only the bombers, the US would be left with no counterforce approach, as both the Navy and Air Force missiles could only attack large targets.
As the US Navy was quick to point out, their Polaris fleet's stealth and mobility would maintain a countervalue force under any possible scenario. This threatened the Air Force's supremacy in the nuclear warfighting arena. Even in the case of a counterforce attack, their bombers would take hours to complete their missions, during which the Soviets could launch their remaining missiles. The Air Force could not let this stand, and following the advice of RAND Corporation, in 1962 they decided the solution was to make the Minuteman capable of counterforce missions as well. The changes to Minuteman II were two-fold. One was to introduce the NS-17 inertial navigation system, which improved the CEP to and allowed the missiles to attack Soviet silos directly. The other was to allow the missiles to quickly switch between a selection of eight targets, allowing them to be fired at only those Soviet silos that had not already launched.
Golden Arrow
Similar improvements to Soviet missiles, real or imagined, led to US officials proposing a worrying scenario; a Soviet first strike with a limited number of warheads aimed at the Minuteman silos or control bunkers could cripple the US ICBM fleet. At the time, the Soviets were only capable of mounting a limited attack. With the limited accuracy of Soviet missiles, only an attack with a small number of missiles carrying very large warheads was feasible. They had just enough of these to make a damaging, but not decisive, attack on the US ICBM fleet. This scenario was of deep concern to the Air Force as it became ever more dependent on Minuteman for most strategic missions.The Air Force had depended on engineering support from TRW during the early days of the development of their ICBM force. In 1960 a number of TRW and other engineers involved in the ICBM program formed The Aerospace Corporation, initially working on the Mercury spacecraft, X-20 Dynasoar and various ICBM projects. In 1964, the Air Force contracted them to consider a wide variety of survivable ICBM approaches, under the name "Golden Arrow".
The project considered road, rail, submarine and air-launched weapons. One of these suggested an air-launched ballistic missile. The proposal called for an enormous turboprop-powered aircraft with two-day endurance carrying up to eight missiles that would be dropped out the back, parachuted to the vertical, and then launched. As part of the same study, Aerospace also considered a missile and wheeled launcher combination that was small enough that they could be carried in existing C-141 Starlifter aircraft. During periods of heightened tensions, they would be flown to practically any airport and set up. The Soviets would have to target thousands of airports, runways and even dirt strips and long stretches of highway to attack the fleet.
Finally, they also considered conventional missiles in "super hard" silos, buried under the southern side of mountains. As the enemy warheads would approach at a fairly shallow angle from the north, they would strike the north side of the mountains before they could hit the silos themselves. Properly positioned, this would keep the explosions at least away from the silos; it was believed that silos able to withstand multi-megaton explosions at one mile could be built, although this was an area of some uncertainty. This system had the advantage that the basing would be immune to changes in the accuracy or speed of the attack, only enormous increases in yield could overcome this physical barrier.
They proposed 100 missiles in three bases of 30 missiles each. They expected that at least one base would be able to survive even an all-out attack. However, if such a force of approximately 30 missiles was going to be a reasonable deterrent, each missile would need to carry 20 or more warheads. To launch them, the study introduced the "ICBM-X", a massive new diameter design, well over twice the diameter of the existing LGM-30 Minuteman, and larger even than the Titan II "heavy" design at.
Any of the "Golden Arrow" concepts would be extremely expensive, and in the era of Robert McNamara's US Department of Defense, cost was as important as any other consideration. As Alain Enthoven put it, "Our gross national product, though large, is limited. If we attempted to develop and procure a dozen or more distinct different nuclear delivery systems… we doubtless would end up squandering our resources and not doing a good job on any of them." Golden Arrow, along with many similar proposals from other firms, proceeded no further, in favor of the Minuteman II.
WS-120A
In 1966 and 67, the Department of Defense ran the STRAT-X study to consider many of these issues. As part of this program, they proposed a smaller version of ICBM-X with 10 to 20 warheads. Known initially as WS-120A and later as BGM-75 AICBM, the missile was small enough to fit in existing large silos, like those for the Titan II, but was otherwise similar in concept to the ICBM-X, with a circular error probable of about, and especially the ability to be quickly re-programmed to attack any targets needed. In comparison, the Minuteman II had a selection of eight targets, any one of which could be quickly selected for attack, but otherwise selecting a target outside this pre-computed list was not something that could be done "on the fly". WS-120A's preferred basing mode was a super-hardened shelter, but dispersed mobile options were also considered.However, like Golden Arrow before it, WS-120A's advantages found themselves being diluted by the new Minuteman III. The Minuteman III used the new NS-20 inertial navigation system with a CEP of, three warheads and an expanded collection of radar countermeasures that would ensure the warheads would survive an anti-ballistic missile attack. Although the system did not include the ability to be rapidly retargeted, this capability was under development and started deployment in 1972, before the planned 1975 introduction date of WS-120A. When it was fully deployed in 1978, the entire ICBM fleet could be entirely reprogrammed in 10 hours.