Vanguard - class submarine The " Vanguard " - class are a class of nuclear - powered ballistic missile submarine s ( SSBN ) in service with the Royal Navy . Each submarine is armed with up to 16 Trident II missiles . The class was introduced in 1994 as part of the UK government ' s Trident nuclear weapons program me . The class includes four boats : " Vanguard " , " Victorious " , " Vigilant " and " Vengeance " . They were built at Barrow - in - Furness by Vickers Shipbuilding and Engineering between 1986 and 1999 . All four boats are based at HM Naval Base Clyde ( HMS " Neptune " ) , west of Glasgow , Scotland . Since the decommissioning of the Royal Air Force WE . 177 free - fall nuclear bombs in 1998 , the four " Vanguard " submarines are the sole platforms for the United Kingdom ' s nuclear weapons . Development . Since the late 1960s , the UK had operated four Resolution class submarine s armed with US - built Polaris missiles under the terms of the 1963 Polaris Sales Agreement . On 10 July 1980 , Prime Minister Margaret Thatcher wrote to US President Carter to request the supply of Trident I ( C4 ) missiles on a similar basis for the United Kingdom ' s next generation ballistic missile submarines . However in 1982 Thatcher wrote to US President Reagan to request the UK be allowed to procure the improved Trident II ( D5 ) system , which had been accelerated by the US Navy . This was agreed in March 1982 . Under the agreement , the United Kingdom made a 5 % research and development contribution . Thatcher laid the keel of the first boat , HMS " Vanguard " , on 3 September 1986 . Operational history . The Trident II D - 5 achieved an initial operational capability with the U . S . Navy in March 1990 . Following launch and commissioning the vessels deployed on Demonstration and Shakedown Operations ( DASOs ) which included test firing of Trident missiles at the United States ' SLBM Launch Area , Eastern Test Range , Cape Canaveral , off the coast of Florida . In February 2002 , " Vanguard " began a two - year refit at HMNB Devonport . The refit was completed in June 2004 and in October 2005 " Vanguard " completed her return to service trials ( Demonstration and Shakedown Operations ) with the firing of an unarmed Trident missile . During this refit , " Vanguard " was illegally boarded by a pair of anti - nuclear protestors . Mid - life refits for " Victorious " and " Vigilant " followed , with " Vengeance " currently undergoing this process . In 2002 , protesters from Trident Ploughshares breached security at Faslane Naval Base where the " Vanguard " submarines are based . Two protesters managed to spraypaint " Vigilant " with the CND symbol and the word " Vile " . On 4 February 2009 , " Vanguard " collided with the French submarine " Triomphant " in the Atlantic . She returned to Faslane in Scotland , under her own power arriving on 14 February 2009 . On 31 March 2011 , " Vengeance " returned to Faslane naval base on the surface after developing mechanical problems while on a training exercise . According to the MOD the problems were not nuclear related . In June 2012 , HMS Vigilant completed a three - year long refit which included refuelling of her nuclear reactor and costing over £300 million . In October 2012 , the submarine sailed to the USA where it successfully test fired an unarmed Trident II D5 SLBM . However , two months later it was learned that shortly afterwards the submarine suffered unspecified problems , allegedly involving her rudder , prompting an unscheduled stop at the US Navy ' s Naval Submarine Base Kings Bay in order to carry out repairs . Replacement programme . A decision on the replacement of Trident was made on the 4 December 2006 . Then - Prime Minister Tony Blair told MPs it would be " unwise and dangerous " for the UK to give up its nuclear weapons . He outlined plans to spend up to £20 billion on a new generation of submarines for Trident missiles . He said submarine numbers may be cut from four to three , while the number of nuclear warheads would be cut by 20 percent to 160 . Blair said although the Cold War had ended , the UK needed nuclear weapons , as no - one could be sure another nuclear threat would not emerge in the future . The 2006 white paper stated that the option of reducing the Trident carrying submarine fleet from four to three submarines , as part of plans to cut costs and to promote nuclear disarmament , would be considered . On 23 September 2009 , Prime Minister Gordon Brown confirmed that this reduction to three submarines was still under consideration . In February 2011 , the Defence Secretary Liam Fox stated that four submarines would be needed if the UK was to retain its current capabilities . On 18 May 2011 the British government approved the initial assessment phase for the construction of new Trident submarines , paving the way for the ordering of the first long - lead items and preparations for the main build to begin in the future . The new submarine class will retain the current Trident II missiles , and will incorporate a new ' PWR3 ' nuclear reactor as well as technology developed for the " Astute " - class SSNs . The final decision whether to build three or four submarines will be taken in 2016 . The cost for four boats is estimated to be £15 – 20 billion at 2006 / 7 prices , and they will have a projected life span of more than 25 years . Characteristics . The " Vanguard " class was designed and built at Barrow - in - Furness by Vickers Shipbuilding and Engineering , now BAE Systems Submarine Solutions . The Devonshire Dock Hall was built specifically for the construction of the submarines . The missile compartment is based on the system used on the American , although only 16 missiles are fitted , rather than the 24 equipped on the " Ohio " class . The " Vanguard " submarines were designed from the outset as nuclear - powered ballistic missile platforms to accommodate the Trident D - 5 submarine - launched ballistic missile . This required the boats to be significantly larger than the previous Polaris - equipped Resolution class , and they are some of the largest submarines ever built , only eclipsed by the American " Ohio " - class , and Russian " Typhoon " - and " Borei " - class submarines . In addition to the missile tubes , the submarines are fitted with four 21 inch ( 533 mm ) torpedo tubes and carry the Spearfish heavyweight torpedo allowing them to engage submerged or surface targets at ranges up to . Two SSE Mark 10 launchers are also fitted allowing the boats to deploy Type 2066 and Type 2071 decoys , and a UAP Mark 3 electronic support measures ( ESM ) intercept system is carried . A ' Core H ' reactor is fitted to each of the boats during their long - overhaul refit periods , ensuring that none of the submarines will require further re - fuelling for the rest of their service lives . The boats are capable of deploying with a maximum of 192 independently targetable warheads , or MIRVs , with immediate readiness to fire . However , as a result of a decision taken by the 1998 Strategic Defence Review this was reduced to 48 warheads with a readiness to fire reduced ' to days rather than minutes ' . Furthermore the total number of warheads maintained by the United Kingdom was reduced to approximately 200 , with a total of 58 trident missiles . The reduced warhead load per missile allowed the development of lower - yield non - strategic warheads loading options . The 2010 Strategic Defence and Security Review reduced this number further and the submarines will put to sea in future with a reduced total of 40 warheads and a reduced missile load of 8 ( from a maximum possible 16 ) . The number of operationally available nuclear warheads is to be reduced ' from fewer than 160 to no more than 120 ' and the total UK nuclear weapon stockpile will number no more than 180 . " Vanguard " , " Victorious " , " Vigilant " and " Vengeance " were commissioned in 1993 , 1995 , 1996 and 1999 respectively . A new pressurised water reactor , the Rolls - Royce PWR 2 , was designed for the " Vanguard " class . This has double the service life of previous models , and it is estimated that a " Vanguard " class submarine could circumnavigate the world 40 times without refuelling . The reactor drives two GEC steam turbines linked to a single shaft pump jet propulsor giving the submarines a maximum submerged speed of . Auxiliary power is provided by a pair of 6 MW steam - turbine generators supplied by WH Allen , ( later known as NEI Allen , Allen Power & Rolls - Royce ) , and two , 2 MW Paxman diesel alternators for provision of backup power supply . A specialised Submarine Command System ( SMCS ) was originally developed for the " Vanguard " boats and was later used on the " Trafalgar " - class . The submarines carry the Thales Underwater Systems Type 2054 composite sonar . The Type 2054 is a multi - mode , multi - frequency system , which incorporates the 2046 , 2043 and 2082 sonars . The Type 2043 is a hull - mounted active / passive search sonar , the Type 2082 a passive intercept and ranging sonar , and the Type 2046 a towed array sonar operating at very low frequency providing a passive search capability . The fleet is in the process of having the sonars refitted to include open - architecture processing using commercial off the shelf technology . Navigational search capability is provided by a Type 1007 I - band navigation radar . Two periscope s are carried , a CK51 search model and a CH91 attack model . Both have TV and thermal imaging cameras in addition to conventional optics .