GAM-87 Skybolt

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), equipped with a thermonuclear warhead, developed by the United States during the late 1950s. 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 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 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 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 much more dangerous and had greatly reduced the effective deterrent power of a bomber force. Yet the Air Force and military planners were, in the mid-1950s, reluctant to simply hand over the nuclear strike capability to missiles. After launch, missiles 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. Bombers, in comparison, could be re-directed in flight, and their longer flight times offered greater chance of a negotiated settlement during the attack.

Furthermore, the missiles of the day were all required to be loaded with their fuels immediately prior to launch, and they could only be launched from above ground after long pre-launch checkouts. This made them vulnerable to attack from the air while they prepared – the first American ICBMs, Atlas 1 and Titan 1, were of this type (Soviet R-7 suffered from the same problem as well). In contrast, a bomber could be ordered into the air long in advance of an attack, rendering them effectively invulnerable to attack while they "loitered" awaiting orders. With aerial refuelling, the loiter times were on the order of a day if need be.

In addition, the inaccuracy 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, or 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 an intriguing prospect to 1950s military planners.


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 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 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 cancelled 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 programme was formally cancelled in April 1960 and in May 1960 an agreement for an initial order of 100 Skybolts was concluded.[2]

Avro were made an associate contractor to manage the Skybolt programme 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. The first fully successful flight occurred on December 19, 1962.


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 December 22, 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.

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.


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



Further reading

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