[3] The British government trusted that the United States would continue to share nuclear technology, which it regarded as a joint discovery,[4] but the 1946 McMahon Act ended cooperation.

[5] Fearing a resurgence of United States isolationism, and Britain losing its great power status, the British government restarted its own development effort,[6] now codenamed High Explosive Research.

[8][9] The subsequent British development of the hydrogen bomb, and a favourable international relations climate created by the Sputnik crisis, led to the McMahon Act being amended in 1958, and the restoration of the nuclear Special Relationship in the form of the 1958 US–UK Mutual Defence Agreement (MDA), which allowed Britain to acquire nuclear weapons systems from the United States.

In 1953, work began on a medium-range ballistic missile (MRBM) called Blue Streak,[11] but by 1958, there were concerns about the vulnerability of this liquid-propellant-missile to a pre-emptive nuclear strike.

[15] An institutional challenge to Skybolt came from the United States Navy, which was developing a submarine-launched ballistic missile (SLBM), the UGM-27 Polaris.

[19] The Prime Minister, Harold Macmillan, met with the President, Dwight D. Eisenhower, in March 1960, and secured permission to buy Skybolt.

[15] The subsequent American decision to cancel Skybolt created a political crisis in the UK, and an emergency meeting between Macmillan and President John F. Kennedy was called in Nassau, Bahamas.

Kennedy ultimately relented, and agreed to supply Britain with Polaris missiles, while "the Prime Minister made it clear that except where Her Majesty's Government may decide that supreme national interests are at stake, these British forces will be used for the purposes of international defence of the Western Alliance in all circumstances.

Vice Admiral Michael Le Fanu had a meeting with the United States Secretary of Defense, Robert S. McNamara, on 21 December 1962, the final day of the Nassau conference.

[26] The First Sea Lord, Admiral of the Fleet Sir Caspar John, denounced the "millstone of Polaris hung around our necks" as "potential wreckers of the real navy".

[32] A mission led by Sir Solly Zuckerman, the Chief Scientific Adviser to the Ministry of Defence, left for the United States to discuss Polaris on 8 January 1963.

His CPE staff was divided between London and Foxhill, near Bath, Somerset, where Royal Navy had its ship design, logistics and weapons groups.

The Zuckerman mission came out in favour of the new A3 missile, although it was still under development and not expected to enter service until August 1964, as the deterrent would remain credible for much longer.

A presidential determination was required to release information on the W58 under the MDA, but with this in hand, a mission led by John Challens, the Chief of Warhead Development at the AWRE, visited the Lawrence Livermore Laboratory from 22 to 24 January 1963, and was shown details of the W58.

[37] Macmillan instructed the British Ambassador to the United States, Sir David Ormsby-Gore, to inform Kennedy that Britain was not willing to commit to an open-ended sharing of research and development costs, but, as a compromise, would pay an additional five per cent for each missile.

McNamara, certain that the United States was being ripped off, calculated the five per cent on top of not just the missiles, but their fire control and navigation systems as well, adding around £2 million to the bill.

This was led by Paul H. Nitze, the Assistant Secretary of Defense for International Security Affairs, and included Walt W. Rostow, the Director of Policy Planning at the State Department, and Admiral Ignatius J. Galantin, the head of the SPO.

They foresaw the UK Polaris programme having project officers from both countries, with a Joint Steering Task Group that met regularly to provide advice.

[40] However, a follow-up British mission under Leslie Williams, the Director General Atomic Weapons at the Ministry of Aviation, whose members included Challens and Rear Admiral Frederick Dossor, was given a letter by the SPO with a list of subjects that were off limits.

[51] The annual running costs of the Polaris boats came to around two per cent of the defence budget, and they came to be seen as a credible deterrent that enhanced Britain's international status.

[55] The United Kingdom procured the Trident system from America and fitted them to their own submarines, which had only 16 missile tubes like Polaris rather than the 24 in the American Ohio class.