AGM-48 Skybolt

AGM-48 Skybolt

The Douglas GAM-87A "Skybolt" was an air-launched ballistic missile (ALBM) developed during the late 1950s. It was intended to provide a mobile basing for the USAF's ICBM missile force by mounting them on heavy bombers rather than in fixed missile silos. The UK joined the program in 1960, intending to use it on their V bomber force. A series of test failures and the development of submarine launched ballistic missiles (SLBMs) eventually led to its cancellation in the mid-1960s. The UK had decided to base its entire 1960's deterrent force on Skybolt, and its cancellation led to a major confrontation between the UK and US, known today as the "Skybolt Crisis". This was solved during 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.



Nuclear weapons theorists had speculated about how to integrate the flexibility and positive control (over the attack) of the manned bomber with the invulnerability (in the attack) of the ballistic missile. The introduction of useful surface-to-air missiles in the 1950s rendered flight over enemy territory nearly suicidal. Yet the Air Force and military planners were, in the mid-1950s, reluctant to simply hand over the nuclear strike capability to missiles, which after launch were no longer under positive control, could not be recalled or redirected, and would reach their targets within a matter of minutes after the order to fire.

In addition, the accuracy of missiles in the 1950s made them useless as precision strike weapons. They could attack area targets like cities, but could not reliably, and accurately, attack precision strike targets like enemy bomber bases, hardened command and control centers, naval bases and weapons storage areas. Initially, western ballistic missiles could not even reach such targets, which would be located deep within interior of the Sino-Soviet land mass in Asia. Therefore the potential integration of aircraft with the invulnerability of the ballistic missile was intriguing prospect to 1950s military planners.

Basing the strike package on aircraft offered flexibility that missiles could not. 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 conventional bombs.

Secondly, and most importantly, this method for the employment 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 either launches or it doesn't, and when threatened with a nuclear strike the best option is to immediately attack in an effort to catch the missiles in their silos.

For the British, their dilemma was simply a matter of geography and financial resources. No fixed land based ballistic missile system could be credibly installed in the British Isles; they were well within the range of Soviet air strikes, and the limited land mass available meant it would be relatively easy for the missile silos to be spotted no matter what security measures were taken. Fixed land based ballistic missiles need many thousands of acres per squadron (typically ten missiles) for the silos; 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 US 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, similar to that of the US Navy's SLBM systems, led to an accuracy similar to that of their existing ground-based missiles.

The USAF 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 (guidance system), Aerojet (propulsion), and General Electric (reentry vehicle). Initially being known as WS-138A, in 1960 the project was given the name GAM-87 Skybolt.

At the same time the Royal Air Force was having problems with their IRBM missile project, the Blue Streak, which was long overdue. At the same time, they faced the same problems with the dwindling survivability of their existing nuclear deterrent, the V-bomber fleet. The long-range Skybolt would eliminate the need for both the Blue Streak and the Blue Steel II standoff missile, then under development.

Prime Minister Macmillan met President Eisenhower in May 1960 and agreed to purchase 144 Skybolts for the RAF, and Blue Streak and Blue Steel II were both cancelled. By agreement, British funding for research and development was limited to that required to modify the V-bombers to take the missile.


By 1961, several test articles were ready for testing from USAF B-52 bombers, with drop-tests starting in January. In England compatibility trials with mockups started on the Vulcan. 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. The first fully successful flight occurred on December 19, 1962.


By this point the value of the Skybolt system had been seriously eroded. The Navy's Polaris SLBM 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 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 cancellation of the Skybolt program as unnecessary.

The British, on the other hand, had cancelled 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?" 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” [John Dumbrell, [ "A special relationship: Anglo-American relations from the Cold War to Iraq"] , Palgrave Macmillan, 2006, p. 174] 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 administration.

Limited flight tests with the remaining XGAM-87A missiles continued after program cancellation. In June 1963, the XGAM-87A was redesignated as XAGM-48A.


The GAM-87 was powered by a two-stage solid-fuel rocket motor. Each B-52H was to carry four missiles, two under each wing on side-by-side pylons, while the Avro Vulcan carried one each on smaller 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.


* RAF Museum Cosford, RAF Cosford, Shropshire (GAM-87)


* Length: 11.66 m (38 ft 3 in)
* Span: 1.68 m (5 ft 6 in)
* Diameter: 89 cm (35 in)
* Weight: 5,000 kg (11,000 lb)
* Speed: 15,300 km/h (9,500 mph)
* Ceiling: 480+ km (300+ miles)
* Range: 1,850 km (1,150 miles)
* Propulsion: Aerojet General two-stage solid-fueled rocket
* Warhead: W-59 1.2 MT thermonuclear

ee also

* "M-" sequence missiles: AGM-45 - MIM-46 - AIM-47 - AGM-48 - LIM-49 - RIM-50 - MGM-51
* "B-" sequence missiles: XRM-84 - XRM-85 - XRM-86 - GAM-87 - SRM-88 - XRM-89 - XRM-90

* List of military aircraft of the United States
* List of missiles by nation


Further reading

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

External links

* [ Skybolt]
* [ XH537 Skybolt]

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