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The United Kingdom's Polaris programme, officially named the British Naval Ballistic Missile System, provided its first submarine-based nuclear weapons system. Polaris was in service from 1968 to 1996.
Polaris itself was an operational system of four Resolution-class ballistic missile submarines, each armed with 16 Polaris A-3 ballistic missiles. Each missile was able to deliver three ET.317 thermonuclear warheads. This configuration was later upgraded to carry two warheads hardened against the effects of radiation and nuclear electromagnetic pulse, along with a range of decoys.
The British Polaris programme was announced in December 1962 following the Nassau Agreement between the US and the UK. The Polaris Sales Agreement provided the formal framework for cooperation. Construction of the submarines began in 1964, and the first patrol took place in June 1968. All four boats were operational in December 1969. They were operated by the Royal Navy, and based at Clyde Naval Base on Scotland's west coast, a few miles from Glasgow. At least one submarine was always on patrol to provide a continuous at-sea deterrent.
In the 1970s it was considered that the re-entry vehicles were vulnerable to the Soviet anti-ballistic missile screen concentrated around Moscow. To ensure that a credible and independent nuclear deterrent was maintained, the UK developed an improved front end named Chevaline. There was controversy when this project became public knowledge in 1980, as it had been kept secret by four successive governments while incurring huge expenditure. Polaris patrols continued until May 1996, by which time the phased handover to the replacement Trident system had been completed. (Full article...)