GAM-87 Skybolt

The Douglas GAM-87 Skybolt, redesignated AGM-48 under the 1963 Tri-service system, was an air-launched ballistic missile (ALBM) developed by the United States during the late 1950s. The basic concept was to allow US strategic bombers to launch their weapons from well outside the range of Soviet defenses, as much as from their targets. To do this in an air-launched form, a lightweight thermonuclear warhead was needed. Initially, the W47 from the Polaris missile was selected, but it was later replaced by the W59 from the Minuteman missile.

The UK joined the Skybolt program in 1960, intending to use it on their V bomber force. When the design added a star tracker in addition to its inertial navigation system (INS) this meant that it could only be carried externally where the tracker could see the sky. This requirement, along with the required ground clearance on takeoff, limited it to the Avro Vulcan bomber. Several design decisions in the W47 led the RAF to question its safety, so they intended to use their own Red Snow warheads. This was a heavier warhead and would reduce the range to about , meaning the bombers would have to cross the Soviet coastline to attack Moscow.

Testing began in 1962 and was initially marked by a string of failures. These failures, along with a lack of mission after the successful development of submarine-launched ballistic missiles (SLBMs), led to its cancellation in December 1962. The UK had decided to base its entire 1960s deterrent force on Skybolt, and its cancellation led to a major disagreement between the UK and US, known today as the "Skybolt Crisis". This was resolved by a series of meetings that led to the Royal Navy gaining the UGM-27 Polaris missile and construction of the s to launch them.

History

Background

The US Air Force had built up an enormous fleet of strategic bombers during the 1950s, only to see them threatened by the possibility of a surprise attack by Soviet ICBMs. As the US bombers were located at only a small number of air bases, a relatively small fleet of missiles could attack all of them at once. The US had been developing its own ICBMs as well, but early models, like the SM-65 Atlas, required some time to prepare to launch from their surface launchers and were vulnerable to sneak air attack. A carefully timed attack from Soviet bombers against US missiles and their ICBMs against US bomber fields could inflict serious damage.

The one weapon system that was not open to attack was the US Navy's Polaris missile system. The Polaris equipped submarines could cruise in large areas of the Atlantic or Pacific where the Soviet fleet was unable to find them, and launch their missiles with impunity. If the goal of the nuclear force was to maintain deterrence by ensuring that a counterstrike would be launched, Polaris met this goal in a way the existing Air Force fleet could not. The possible loss of the nuclear role to the Navy was more worrying to the Air Force than the Soviet arsenal and generated a number of internal reports on how to deal with this threat to their dominance in the strategic field.

WS-199 was generally successful, but the two ALBMs had a shorter range than desired. The Air Force tendered bids for a longer-range version in early 1959. Douglas Aircraft received the prime contract in May, and in turn subcontracted to Northrop for the guidance system, Aerojet for the propulsion system, and General Electric for the reentry vehicle. The system was initially known as WS-138A and was given the official name GAM-87 Skybolt in 1960.

British involvement

thumb|right|Skybolt at [[Royal Air Force Museum Midlands Showing the RAF roundel and the manufacturer (Douglas Aircraft) logo. It carries the tail-cone fairing that reduces drag in flight.]]

At the same time, the Royal Air Force (RAF) was having problems with their MRBM missile project, the Blue Streak, which was long overdue. Even if this was successful it faced the serious problem of basing. No fixed land-based missile system could be credibly installed in the British Isles; they were well within the range of Soviet air strikes. The limited land mass available meant it would be relatively easy for missile sites to be spotted no matter what security measures were taken, and flying time for a jet bomber from the coast to any potential inland location would be on the order of minutes.

This left the deterrent based on their own bomber force, the V bomber fleet, which the RAF had already long concluded would be unable to penetrate Soviet defenses by about 1960. The RAF was in the process of introducing their own stand-off missile, the ranged Mach 3 Blue Steel. While capable, the missile flew at altitudes and speeds that left it vulnerable to improving SAMs, and it had a number of reliability and serviceability issues that made it less than ideal. A faster, longer-ranged version was being talked about, Blue Steel II, but it would be some time before it could enter service.

The long-range Skybolt would eliminate the need for both the Blue Streak and the Blue Steel II. Blue Steel II was canceled in December 1959 and the British Cabinet decided in February 1960 to cancel Blue Streak as well. Prime Minister Macmillan met President Eisenhower in March 1960 and agreed to purchase 144 Skybolts for the RAF. By agreement, British funding for research and development was limited to that required to modify the V bombers to take the missile, but the British were allowed to fit their own warheads. In exchange, the Americans were given nuclear submarine basing facilities in Scotland.

Cancellation

By this point, the perceived value of the Skybolt system to Robert McNamara had been seriously eroded. The Polaris had recently gone into service, with overall capabilities similar to Skybolt, but with "loiter" times on the order of months instead of hours. The US Air Force was well into the process of developing the Minuteman missile, whose improved accuracy reduced the need for any bomber attacks. Robert McNamara was particularly opposed to the bomber force and repeatedly stated he felt that the combination of SLBMs and ICBMs would render them useless. He pressed for the cancellation of Skybolt as unnecessary.

The British had canceled all other projects to concentrate fully on Skybolt. When McNamara informed them that they were considering canceling the program in November 1962, a firestorm of protest broke out in the House of Commons. Jo Grimond noted "Does not this mark the absolute failure of the policy of the independent deterrent? Is it not the case that everybody else in the world knew this, except the Conservative Party in this country?" President Kennedy officially cancelled the program on 22 December 1962. The RAF kept a tactical nuclear capability with the WE.177 which armed V bombers and later the Panavia Tornado force.

A B-52G launched the last XGAM-87A missile at the Atlantic Missile Range a day after the program was canceled. In June 1963, the XGAM-87A was redesignated as XAGM-48A.

Description

The GAM-87 was powered by a two-stage solid-fuel rocket motor. The missile was fitted with a tailcone to reduce drag while on the pylon, which was ejected shortly after being dropped from the plane. After first stage burnout, the Skybolt coasted for a while before the second stage ignited. First stage control was by eight movable tail fins, while the second stage was equipped with a gimballed nozzle.

Guidance was entirely by inertial platform. The current position was constantly updated from the host aircraft through accurate fixes, meaning that the accuracy of the platform inside the missile was not as critical.

B-52s were to carry four missiles, two under each wing on the weapons pylon with a dual launcher adapter with the missiles slightly staggered (inboard missile slightly ahead of the outboard missile). The Vulcan carried two missiles, one each on smaller underwing pylons.

Survivors

Royal Air Force Museum Midlands, Shropshire, England
National Museum of the United States Air Force, Dayton, Ohio, United States
Air Force Space & Missile Museum, Cape Canaveral Air Force Station, Florida, United States

References

Bibliography

External links

Skybolt, Encyclopedia Astronautica