In 1962, with the “Skybolt crisis,” which arrived when the promised GAM-87 Skybolt cruise missile tanked, leaving British Vulcan bombers hamstrung, the Royal Navy announced they would add a ballistic missile program to HMs Submarines and moved to produce five Resolution-class SSBNs, a 8,400-ton vessels each armed with 16 U.S.-made UGM-27 Polaris A-3 ballistic missiles, each able to deliver three British-made 200 k ET.317 warheads in the general area of a single metropolitan-sized target. This enabled a single British Polaris boomer on patrol to plaster the 16 most strategic targets in the CCCP.

HMS RESOLUTION, BRITAIN’S FIRST POLARIS SUBMARINE. JUNE 1967, DURING SPEED TRIALS AFTER LEAVING VICKERS SHIPYARD, BARROW-IN-FURNESS. (A 35095) HMS RESOLUTION at speed during her trials. Copyright: © IWM. Original Source: http://www.iwm.org.uk/collections/item/object/205016469
With all of the moving parts and ominous tasking, the Resolutions, a modified Valiant-class design, were given traditional battleship/battlecruiser names (Resolution, Repulse, Renown, Revenge, and Ramillies) though just four were ultimately completed.
On 15 February 1968, HMS Resolution fired the first British Polaris on a test range off Florida and on 15 June began her first deterrent patrol.
Now, fast forward 49 years and the British have announced that between the four Resolutions and the four follow-on Vanguard-class Trident missile boats (also named for battleships) that replaced them in the 1990s, the force has completed 350 patrols, with at least one at sea at any given time, ready in case the world needs a nuke fed-exed. They also advise there has never been a time since then that a Brit SSBN has not been out there lurking somewhere drinking tea and running EAM missile drills.
“That the Royal Navy has completed 350 deterrent patrols without once breaking the chain is simply a momentous achievement,” said Rear Admiral John Weale OBE, Head of the UK Submarine Service. “Everyone knows that a chain is only as strong as its weakest link. Whether it is the dedication of our submariners, the expertise of our engineers and support staff, or the love of our families– each link remained strong throughout.”
The RN is planning to replace the Valiants with the Dreadnought-class, which will be the most expensive undersea warships ever built in Europe but will keep the UK with an SLBM option into the 2060s, at which point they will have been in the buisness for going on 100 years.