GAM-87 Skybolt

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GAM-87 Skybolt
Type Air-launched ballistic missile
Production history
Manufacturer Douglas Aircraft, Northrop
Weight 11,000 pounds (5,000 kg)
Length 38 feet 3 inches (11.66 m)
Diameter 35 inches (890 mm)
Warhead W59 thermonuclear weapon (1 megaton)

Engine Aerojet General two-stage solid-fuel rocket
Wingspan 5 feet 6 inches (1.68 m)
1,150 miles (1,850 km)
Flight ceiling >300 miles (480 km)
Speed 9,500 miles per hour (15,300 km/h)
inertial guidance

The Douglas GAM-87 Skybolt (AGM-48 under the 1962 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 1,000 miles (1,600 km) from their targets. To do this in an air-launched form, a lightweight thermonuclear warhead was needed, initially selecting the W47 from the Polaris missile, but later moving to 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) and the requirement for ground clearance on takeoff limited it to the Avro Vulcan bomber. A number of design decisions in the W47 led the RAF to question its safety, so they intended to use their own Red Snow warheads in place of the W47. This was a heavier warhead and would reduce the range to about 600 miles (970 km), meaning it 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.[1] 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 Resolution-class submarines to launch them.



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 them all. The US had been developing its own ICBMs but early models like the SM-65 Atlas required some time to prepare to launch from their surface launchers and were likewise open to sneak attack.

The one weapon system that was not open to attack was the US Navy's Polaris missile system. The Polaris 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. This fact was more disconcerting to the Air Force than the Soviet fleet and generated a number of internal reports on how to deal with this threat to their dominance in the strategic field.


In response, in 1957 the Air Force began studying solutions to the "Puzzle of Polaris" under the WS-199 program. WS-199 was a grab-bag effort, studying anything that might improve the survivability of the Air Force strike capability. Primary among these were two air-launched ballistic missiles, Bold Orion and High Virgo. These systems would give the Air Force a system somewhat similar to the Navy's; in times it high alert, the bomber force would be sent to holding positions far outside the range of any Soviet defenses, and then launch their missiles on command. Using aerial refuelling, a bomber might be expected to be able to loiter for as long as a day.

But this system had a major advantage compared to Polaris, as the missiles could be targeted before launch. In theory, the bombers could be used as a second-strike weapon, attacking only those targets that had been missed in a first-strike, or alternately being switched from counterforce to countervalue targets or vice-versa. Ground-based systems like Atlas and Polaris lacked this ability, and could only be re-targeted with a significant amount of effort.


Basing the strike package on aircraft offered a flexibility that missiles could not match. For instance, the bombers could stand off from the targets and wait for instructions from secure command centers to attack targets that were missed in an initial strike. Additionally, the bombers could use long-range weapons to strike known air defenses, and then overfly them to deliver precision strikes with freefall nuclear bombs.

Secondly, and most importantly, this mode of deployment meant that the strike force was rendered almost invulnerable. The bombers could fly to staging areas well outside the range of even the longest-legged defenses, and strike with impunity. This allowed for gradual escalation and a possible backing down through diplomacy. A ground-based missile cannot be used in the same fashion; it is either launched or not. If threatened with a nuclear strike, this presents their owners with the 'use them or lose them' predicament.

For the British, their dilemma was a matter of geography and financial resources. 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. Suitable locations for construction also carried a social and political cost. Fixed land based ballistic missile sites need many thousands of acres per squadron (typically ten missiles); and the squadrons need to be apportioned over many thousands of square miles, so that no single attack could conceivably destroy them all in one strike.


In 1958, several American contractors demonstrated that large ballistic missiles could be launched from strategic bombers at high altitude. The use of astronavigation systems for mid-flight corrections of an inertial guidance platform (astro-inertial guidance), similar to that of the US Navy's SLBM systems, led to an accuracy similar to that of their existing ground-based missiles.

The US Air Force was interested and began accepting bids for development systems 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.

Skybolt at RAF Museum Cosford Showing the RAF roundel and the manufacturer (Douglas Aircraft) logo

At the same time, the Royal Air Force (RAF) was having problems with their MRBM missile project, the Blue Streak, which was long overdue. This left the deterrent based on their own bomber force, the V bomber fleet, and like the Americans there were concerned about its survivability in the face of improving Soviet SAMs.

The RAF was in the process of introducing their own stand-off missile, the 950 kilometres (590 mi) 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 designed, 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 standoff missile, then under development. The Blue Steel II was canceled in December 1959 and the British Cabinet decided in February 1960 to cancel the Blue Streak.

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 and the Americans were given nuclear submarine basing facilities in Scotland.[2] Following the agreement, the Blue Streak program was formally canceled in April 1960 and in May 1960 an agreement for an initial order of 100 Skybolts was concluded.[2]

Avro was made an associate contractor to manage the Skybolt program for the United Kingdom and four different schemes were submitted to find a platform for the missile.[2] A number of different aircraft platforms were considered, including a variant of the Vickers VC10 airliner and two of the current V bombers, the Avro Vulcan and Handley Page Victor.[2] It was decided to use the Vulcan to initially carry two missiles each on hardpoints outboard of the main landing gear.[2]


By 1961, several test articles were ready for testing from USAF B-52 bombers, with drop-tests starting in January. In January 1961 a Vulcan visited the Douglas plant at Santa Monica, California, to make sure the modifications to the aircraft were electrically compatible with the missile. In Britain, compatibility trials with mockups started on the Vulcan.[2] Powered tests started in April 1962, but the test series went badly, with the first five trials ending in failure of one sort or another.[citation needed] The first fully successful flight occurred on 19 December 1962.[citation needed]


By this point the value of the Skybolt system had been seriously eroded. The US Navy's Polaris submarine-launched ballistic missile had recently gone into service, with overall capabilities similar to Skybolt, but with "loiter" times on the order of months instead of hours. Additionally, the US Air Force itself 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 an unnecessary program.

The British, on the other hand, had cancelled all other projects to concentrate fully on Skybolt. When McNamara informed them that they were considering cancelling 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?"[3] President Kennedy officially cancelled the program on 22 December 1962.[1] As the political row grew into a major crisis, an emergency meeting between parties from the US and UK was called, leading to the Nassau agreement.

Over the next few days a new plan was hammered out that saw the UK purchase the Polaris SLBM, but equipped with British warheads that lacked the dual-key system. The UK would thus retain its independent deterrent force, although its control passed from the RAF largely to the Royal Navy. The Polaris, a much better weapon system for the UK, was a major "scoop" and has been referred to as "almost the bargain of the century".[4] The RAF kept a tactical nuclear capability with the WE.177 which armed V bombers and later the Panavia Tornado force. The "Skybolt Crisis" was a major event in the eventual downfall of the Macmillan government.[citation needed]

A B-52G launched the last XGAM-87A missile down the Atlantic Missile Range a day after the program was cancelled.[5] In June 1963, the XGAM-87A was redesignated as XAGM-48A.[citation needed]


The GAM-87 was powered by a two-stage solid-fuel rocket motor. B-52s were to carry four missiles, two under each wing on side-by-side pylons while the Avro Vulcan carried two, on smaller underwing pylons. 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 though accurate fixes, meaning that the accuracy of the platform inside the missile was not as critical.


See also[edit]



  • Brookes, Andrew (1982). V Force – The History of Britain's Airborne Deterrent. London: Book Club Associates. 

Further reading[edit]

  • Neustadt, Richard E. Report to JFK: The Skybolt Crisis in Perspective. Ithaca, NY: Cornell University Press, 1999. ISBN 0-8014-3622-2.

External links[edit]

  • Skybolt, Encyclopedia Astronautica