The Resolution class was a class of four nuclear ballistic missile submarines (SSBN) built for the Royal Navy as part of the UK Polaris programme. Each submarine was armed with up to 16 UGM-27 Polaris A-3 nuclear missiles. The class comprised , , and . They were built by Vickers Armstrong in Barrow-in-Furness and Cammell Laird in Birkenhead between 1964 and 1968. All four boats were based at HM Naval Base Clyde (HMS Neptune), west of Glasgow, Scotland. The Resolution class was the launch platform for the United Kingdom's strategic nuclear deterrent from the late 1960s until 1996, when it was replaced by the carrying the Trident II. Background During the 1950s and early 1960s, the United Kingdom's nuclear deterrent was based on the RAF's V-bombers. But in the early 1960s developments in radar and surface-to-air missiles made it clear that bombers were becoming vulnerable, and would be unlikely to penetrate Soviet airspace. Free-fall nuclear weapons would no longer be a credible deterrent. To address this problem, in May 1960 the British Prime Minister, Harold Macmillan arranged a deal with US President Eisenhower to equip the V bombers with the US-designed AGM-48 Skybolt. The Skybolt was a range ballistic missile that allowed the launching bombers to remain well away from Soviet defences and launch attacks that would be basically invulnerable. With this range, the V bombers would have to fly only a few hundred miles from their bases before being in range for an attack on Moscow. Under the agreement the UK's contribution to the programme was limited to developing suitable mounting points on the Avro Vulcan bomber, installing the required guidance systems that fed the missiles updated positioning information, and development of a British version of the US W47 warhead to arm it, the RE.179 . The Skybolt crisis The incoming Kennedy administration expressed serious doubts of both Skybolt and the US deterrent force in general. Robert McNamara was highly critical of the US bomber fleet, which he saw as obsolete in an age of ICBMs. Skybolt was seen simply as a means of continuing the existence of a system he no longer considered credible, and given the rapidly improving capabilities of ICBM inertial guidance systems, a precision strike capability with free-fall bombs would no longer be needed. McNamara was equally concerned about the UK also having its own nuclear force, and worried that the US could be drawn