UK Trident programme

Trident, also known as the Trident nuclear programme or Trident nuclear deterrent, covers the development, procurement and operation of nuclear weapons in the United Kingdom and their means of delivery. Its purpose as stated by the Ministry of Defence is to "deter the most extreme threats to our national security and way of life, which cannot be done by other means". Trident is an operational system of four s armed with Trident II D-5 ballistic missiles, able to deliver thermonuclear warheads from multiple independently targetable re-entry vehicles (MIRVs). It is operated by the Royal Navy and based at Clyde Naval Base on the west coast of Scotland. At least one submarine is always on patrol to provide a continuous at-sea capability. Each one carries no more than eight missiles and forty warheads, although their capacity is higher. The missiles are manufactured in the United States, while the warheads are British.

The British government initially negotiated with the Carter administration for the purchase of the Trident I C-4 missile. In 1981, the Reagan administration announced its decision to upgrade its Trident to the new Trident II D-5 missile. This necessitated another round of negotiations and concessions. The UK Trident programme was announced in July 1980 and patrols began in December 1994. Trident replaced the submarine-based Polaris system, in operation from 1968 until 1996. Trident is the only nuclear weapon system operated by the UK since the decommissioning of tactical WE.177 free-fall bombs in 1998.

NATO's military posture was relaxed after the collapse of the Soviet Union in 1991. Trident warheads have never been aimed at specific targets on an operational patrol, but await co-ordinates that can be programmed into their computers and fired with several days' notice. Although Trident was designed as a strategic deterrent, the end of the Cold War led the British government to conclude that a sub-strategic—but not tactical—role was required.

A programme for the replacement of the ''Vanguard'' class is under way. On 18 July 2016 the House of Commons voted by a large majority to proceed with building a fleet of s, to be operational by 2028, with the current fleet completely phased out by 2032.

Background

During the early part of the Second World War, the United Kingdom (UK) had a nuclear weapons project, code-named Tube Alloys, which the 1943 Quebec Agreement merged with the American Manhattan Project to create a combined American, British, and Canadian project. The British government expected that the United States (US) would continue to share nuclear technology, which it regarded as a joint discovery, but the United States Atomic Energy Act of 1946 (McMahon Act) ended technical co-operation. Fearing a resurgence of US isolationism, and losing its own great power status, the British government resumed its own development effort. The first British atomic bomb was tested in Operation Hurricane on 3 October 1952. The subsequent British development of the hydrogen bomb, and a fortuitous international relations climate created by the Sputnik crisis, facilitated the amendment of the McMahon Act, and the 1958 US–UK Mutual Defence Agreement (MDA), which allowed Britain to acquire nuclear weapons systems from the US, thereby restoring the nuclear Special Relationship.

During the 1950s, Britain's nuclear deterrent was based around the V-bombers of the Royal Air Force (RAF), but developments in radar and surface-to-air missiles made it clear that bombers were becoming increasingly vulnerable, and would be unlikely to penetrate Soviet airspace by the mid-1970s. To address this problem, the UK embarked on the development of a Medium Range Ballistic Missile called Blue Streak, but concerns were raised about its own vulnerability, and the British government decided to cancel it and acquire the American Skybolt air-launched ballistic missile. In return, the Americans were given permission to base the US Navy's Polaris boats at Holy Loch in Scotland. In November 1962, the American government cancelled Skybolt. John F. Kennedy, then President of the United States, and Harold Macmillan, then UK Prime Minister, negotiated the Nassau Agreement, under which the US would sell Polaris systems for UK-built submarines. This was formalised in the Polaris Sales Agreement.

The first British Polaris ballistic missile submarine (SSBN), , was laid down by Vickers-Armstrongs at its yard at Barrow-in-Furness in Cumbria on 26 February 1964. She was launched on 15 September 1965, commissioned on 2 October 1967, and conducted a test firing at the American Eastern Range on 15 February 1968. She was