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{{Short description|Weapon}}
{{Redirect|Trident (nuclear programme)|the US missile programme|Trident (missile)}}
{{good article}}
{{Infobox project
| name = Trident
| image = File:HMS Victorious MOD 45155638.jpg
| caption = {{HMS|Victorious|S29|6}}, a [[Trident (missile)|Trident missile]]-armed {{sclass|Vanguard|submarine}} leaving its base at [[HMNB Clyde]] on a training exercise in 2013
| type = Deployment of Trident [[ballistic missile submarine]]s
| country = United Kingdom
| primeminister =
| key_people =
| established = 1980
| disestablished =
}}
'''Trident''', also known as the '''Trident nuclear programme''' or '''Trident nuclear deterrent''', covers the development, procurement and operation of [[Nuclear weapons and the United Kingdom|nuclear weapons in the United Kingdom]] and their means of delivery. Its purpose as stated by the [[Ministry of Defence (United Kingdom)|Ministry of Defence]] is to "deter the most extreme threats to our national security and way of life, which cannot be done by other means".<ref name="modfeb16">{{cite web|url=https://www.gov.uk/government/publications/uk-nuclear-deterrence-factsheet/uk-nuclear-deterrence-what-you-need-to-know|title=UK nuclear deterrence: what you need to know|publisher=Ministry of Defence|date=26 February 2016|access-date=1 March 2016|archive-date=21 September 2016|archive-url=https://web.archive.org/web/20160921070246/https://www.gov.uk/government/publications/uk-nuclear-deterrence-factsheet/uk-nuclear-deterrence-what-you-need-to-know|url-status=live}}</ref> Trident is an operational system of four {{sclass|Vanguard|submarine}}s armed with [[UGM-133 Trident II|Trident II D-5]] [[submarine-launched ballistic missile|ballistic missiles]], able to deliver [[thermonuclear weapon|thermonuclear warheads]] from [[multiple independently targetable re-entry vehicle]]s (MIRVs). It is operated by the [[Royal Navy]] and based at [[HMNB Clyde|Clyde Naval Base]] on the west coast of Scotland. At least one submarine is always on patrol to provide a continuous at-sea capability. The missiles are manufactured in the United States, while the warheads are British.

The British government initially negotiated with the [[Carter administration]] for the purchase of the [[UGM-96 Trident I|Trident I C-4]] missile. In 1981, the [[Reagan administration]] announced its decision to upgrade its Trident to the new Trident II D-5 missile. This necessitated another round of negotiations and concessions. The UK Trident programme was announced in July 1980 and patrols began in December 1994. Trident replaced the submarine-based [[Polaris (UK nuclear programme)|Polaris]] system, in operation from 1968 until 1996. Trident is the only nuclear weapon system operated by the UK since the decommissioning of tactical [[WE.177]] free-fall bombs in 1998.

[[NATO]]'s military posture was relaxed after the collapse of the Soviet Union in 1991. Trident warheads have never been aimed at specific targets on an operational patrol, but await co-ordinates that can be programmed into their computers and fired with several days' notice. Although Trident was designed as a strategic deterrent, the end of the Cold War led the British government to conclude that a [[Nuclear warfare#Sub-strategic use|sub-strategic]]—but not [[Tactical nuclear weapon|tactical]]—role was required.

A programme for the replacement of the ''Vanguard'' class is under way. On 18 July 2016, the [[House of Commons of the United Kingdom|House of Commons]] voted by a large majority to proceed with building a fleet of {{sclass|Dreadnought|submarine|2}}s, to be operational by 2028, with the current fleet completely phased out by 2032.

==Background==
During the early part of the [[Second World War]], the United Kingdom (UK) had a [[nuclear weapon]]s project, code-named [[Tube Alloys]],{{sfn|Gowing|1964|pp=108–111}} which the 1943 [[Quebec Agreement]] merged with the American [[Manhattan Project]] to create a combined American, British, and Canadian project. The British government expected that the United States (US) would continue to share nuclear technology, which it regarded as a joint discovery, but the [[United States Atomic Energy Act of 1946]] (McMahon Act) ended technical co-operation.{{sfn|Jones|2017|pp=1–2}} Fearing a resurgence of [[United States isolationism|US isolationism]], and losing its own [[great power]] status, the British government [[High Explosive Research|resumed its own development effort]].{{sfn|Gowing|Arnold|1974|pp=181–184}} The first British atomic bomb was tested in [[Operation Hurricane]] on 3 October 1952.{{sfn|Jones|2017|p=25}} The subsequent [[British hydrogen bomb programme|British development of the hydrogen bomb]], and a fortuitous international relations climate created by the [[Sputnik crisis]], facilitated the amendment of the McMahon Act,{{sfn|Grove|1987|pp=230–231}} and the [[1958 US–UK Mutual Defence Agreement]] (MDA), which allowed Britain to acquire nuclear weapons systems from the US, thereby restoring the nuclear [[Special Relationship]].{{sfn|Navias|1991|pp=193–198}}{{sfn|Baylis|2008|p=446}}

[[File:RAF Museum Cosford - DSC08499.JPG|thumb|left|A [[Polaris missile]] at the [[Royal Air Force Museum Cosford]], with [[Chevaline]] (right)]]
During the 1950s, Britain's nuclear deterrent was based around the [[V-bombers]] of the [[Royal Air Force]] (RAF), but developments in [[radar]] and [[surface-to-air missiles]] made it clear that [[bombers]] were becoming increasingly vulnerable, and would be unlikely to penetrate Soviet airspace by the mid-1970s.{{sfn|Brown|1964|pp=294–296}} To address this problem, the UK embarked on the development of a [[Medium Range Ballistic Missile]] called [[Blue Streak (missile)|Blue Streak]],{{sfn|Jones|2017|p=37}} but concerns were raised about its own vulnerability,{{sfn|Moore|2010|pp=42–46}} and the British government decided to cancel it and acquire the American [[AGM-48 Skybolt|Skybolt]] [[air-launched ballistic missile]].{{sfn|Moore|2010|pp=46–48}} In return, the Americans were given permission to base the [[US Navy]]'s [[UGM-27 Polaris|Polaris]] boats at [[Holy Loch]] in Scotland.{{sfn|Moore|2010|pp=64–68}} In November 1962, the American government cancelled Skybolt.{{sfn|Moore|2010|pp=168–169}} [[John F. Kennedy]], then President of the United States, and [[Harold Macmillan]], then UK Prime Minister, negotiated the [[Nassau Agreement]], under which the US would sell Polaris systems for UK-built submarines.{{sfn|Jones|2017|pp=381–393}} This was formalised in the [[Polaris Sales Agreement]].{{sfn|Jones|2017|p=444}}

The first British Polaris [[ballistic missile submarine]] (SSBN), {{HMS|Resolution|S22|6}}, was laid down by [[Vickers-Armstrongs]] at its yard at [[Barrow-in-Furness]] in Cumbria on 26 February 1964.{{sfn|Grove|1987|p=242}}<ref name="Resolution">{{cite web |url=http://rnsubs.co.uk/boats/subs/polaris/resolution.html |title=Resolution (S22) |publisher=Barrow Submariners Association |access-date=17 March 2018 |archive-date=17 March 2018 |archive-url=https://web.archive.org/web/20180317103103/http://rnsubs.co.uk/boats/subs/polaris/resolution.html |url-status=live }}</ref> She was launched on 15 September 1965, commissioned on 2 October 1967,{{sfn|Grove|1987|p=242}} and conducted a test firing at the American [[Eastern Range]] on 15 February 1968.{{sfn|Grove|1987|p=243}} She was followed by {{HMS|Repulse|S23|6}}, which was completed by Vickers-Armstrongs on 29 September 1968;<ref name="Repulse">{{cite web |url=http://rnsubs.co.uk/boats/subs/polaris/repulse.html |title=Repulse (S23) |publisher=Barrow Submariners Association |access-date=17 March 2018 |archive-date=17 March 2018 |archive-url=https://web.archive.org/web/20180317102624/http://rnsubs.co.uk/boats/subs/polaris/repulse.html |url-status=live }}</ref> and two boats built by [[Cammell Laird]] in [[Birkenhead]]: {{HMS|Renown|S26|6}}, which was completed on 15 November 1968;<ref name="Renown">{{cite web |url=http://rnsubs.co.uk/boats/subs/polaris/renown.html |title=Repulse (S26) |publisher=Barrow Submariners Association |access-date=17 March 2018 |archive-date=17 March 2018 |archive-url=https://web.archive.org/web/20180317164723/http://rnsubs.co.uk/boats/subs/polaris/renown.html |url-status=live }}</ref> and {{HMS|Revenge|S27|6}}, which was completed on 4 December 1969.<ref name="Revenge">{{cite web |url=http://rnsubs.co.uk/boats/subs/polaris/revenge.html |title=Revenge (S27) |publisher=Barrow Submariners Association |access-date=17 March 2018 |archive-date=17 March 2018 |archive-url=https://web.archive.org/web/20180317102455/http://rnsubs.co.uk/boats/subs/polaris/revenge.html |url-status=live }}</ref> The four {{sclass|Resolution|submarine|0}} boats were based at [[HMNB Clyde]] at [[Faslane]] on the [[Firth of Clyde]], not far from the US Navy's base at Holy Loch,{{sfn|Nailor|1988|pp=91, 96}} which opened in August 1968. It was served by a weapons store at nearby [[RNAD Coulport]].{{sfn|Grove|1987|p=243}} [[HM Dockyard, Rosyth]], was designated as the refit yard for the [[10th Submarine Squadron (United Kingdom)|10th Submarine Squadron]], as the Polaris boats became operational.{{sfn|Nailor|1988|pp=91, 96}}

[[File:Polaris missile launch from HMS Revenge (S27) 1983.JPEG|thumb|Polaris missile launch from {{sclass|Resolution|submarine|0}} submarine in 1983]]
Polaris proved to be reliable, and its [[second-strike capability]] conferred greater strategic flexibility than any previous British nuclear weapons system. However it had a limited lifespan, and was expected to become obsolete by the 1990s.{{sfn|Priest|2005|pp=369–370}} It was considered vital that an independent British deterrent could penetrate existing and future Soviet [[anti-ballistic missile]] (ABM) capabilities. An ABM system, the [[ABM-1 Galosh]], defended Moscow, and NATO believed the USSR would continue to develop its effectiveness. The deterrent logic required the ability to threaten the destruction of the Soviet capital and other major cities.<ref name="Select Committee Eighth Report">{{cite web|date=20 June 2006|title=The UK's Strategic Nuclear Deterrent|url=https://publications.parliament.uk/pa/cm200506/cmselect/cmdfence/986/98605.htm|access-date=20 May 2012|work=Select Committee on Defence Eighth Report|publisher=House of Commons|archive-date=28 July 2012|archive-url=https://web.archive.org/web/20120728203734/http://www.publications.parliament.uk/pa/cm200506/cmselect/cmdfence/986/98605.htm|url-status=live}}</ref> To ensure that a credible and independent nuclear deterrent was maintained, the UK developed an improved warhead package [[Chevaline]], which replaced one of the three warheads in a Polaris missile with multiple decoys, [[Chaff (radar countermeasure)|chaff]], and other defensive [[countermeasure]]s.<ref name="Chevaline">{{cite web |url=http://nuclearweaponarchive.org//Uk/UKArsenalDev.html |title=History of the British Nuclear Arsenal |publisher= Nuclear Weapons Archive |access-date=16 March 2018}}</ref> Chevaline was extremely expensive; it encountered many of the same issues that had affected the British nuclear weapons projects of the 1950s, and postponed, but did not avert, Polaris's obsolescence.{{sfn|Priest|2005|pp=369–370}}

The [[Conservative Party (UK)|Conservative Party]] had a strong pro-defence stance, and supported the British nuclear weapons programme, although not necessarily at the expense of conventional weapons.{{sfn|Bowie|Platt|1984|pp=40–44}} The rival [[Labour Party (UK)|Labour Party]] had initiated the acquisition of nuclear weapons, but in the late 1950s its left wing pushed for a policy of nuclear disarmament, resulting in an ambiguous stance. While in office from 1964 to 1970 and 1974 to 1979, it built and maintained Polaris, and modernised it through the secret Chevaline programme. In opposition in the early 1980s, Labour adopted a policy of unilateral nuclear disarmament.{{sfn|Bowie|Platt|1984|pp=49–55}}

More important than political differences was a shared sense of British national identity. Britain was seen as an important player in world affairs, its economic and military weaknesses offset by its membership of [[NATO]] and the [[Group of Seven]], its then active membership of the [[European Union]], its permanent seat on the [[UN Security Council]], its leadership of the [[Commonwealth of Nations]], and the nuclear Special Relationship with the US.{{sfn|Ritchie|2008|pp=1–4}} To accept a position of inferiority to its ancient rival, France, was unthinkable.{{sfn|Stoddart|2014|p=195}} Moreover, the UK sees itself as a force for good in the world with a moral duty to intervene, with military force if need be, to defend both its interests and its values.{{sfn|Ritchie|2008|pp=1–4}} By the 1980s, possession of nuclear weapons was considered a visible sign of Britain's enduring status as a great power in spite of the loss of the [[British Empire]], and had become a component of the national self-image.{{sfn|Bowie|Platt|1984|pp=v, 41–44}}{{sfn|Stoddart|2014|p=58}}

==Negotiations==
[[File:Margaret Thatcher visiting Jimmy Carter.jpg|thumb|right|[[Margaret Thatcher]] visits President [[Jimmy Carter]] on 17 December 1979]]
The [[Cabinet Secretary (United Kingdom)|Cabinet Secretary]], Sir [[John Hunt, Baron Hunt of Tanworth|John Hunt]] briefed [[Cabinet of the United Kingdom|Cabinet]] on Polaris on 28 November 1977, noting that a possible successor might take up to 15 years to bring into service, depending on the nature of system chosen, and whether it was to be developed by the UK, or in collaboration with France or the US.{{sfn|Stoddart|2014|p=39}} With the recent experience of Chevaline in mind, the option of a purely British project was rejected.{{Citation needed|date=February 2021}} A study of the options was commissioned in February 1978 from a group chaired by the Deputy Under-Secretary of State at the [[Foreign Office]], Sir [[Antony Duff]], with the [[Chief Scientific Adviser to the Ministry of Defence|Chief Scientific Adviser]] to the [[Ministry of Defence (United Kingdom)|Ministry of Defence]], Sir [[Ronald Mason (chemist)|Ronald Mason]].{{sfn|Doyle|2018|p=3}} The Duff-Mason Report was delivered to the Prime Minister, [[James Callaghan]], in parts on 11 and 15 December.{{sfn|Stoddart|2014|pp=59–60}} It recommended the purchase of the American [[UGM-96 Trident I|Trident I C-4]] missile then in service with the US Navy. The C-4 had [[multiple independently targetable re-entry vehicle]] (MIRV) capability, which was needed to overcome the Soviet ABM defences.{{sfn|Stoddart|2014|pp=61–63}}<ref>{{cite report |title=Duff-Mason Report |publisher=National Archives |date=7 December 1978 |url=http://picat.online/wp-content/uploads/2017/02/The-Duff-Mason-Report.pdf |access-date=27 March 2018 |archive-date=27 March 2018 |archive-url=https://web.archive.org/web/20180327084824/http://picat.online/wp-content/uploads/2017/02/The-Duff-Mason-Report.pdf |url-status=live }}</ref>

Callaghan approached President [[Jimmy Carter]] in January 1979, who responded positively, but did not commit.{{sfn|Doyle|2017a|pp=478–479}} The Carter administration's main priority was the [[SALT II]] Agreement with the Soviet Union, which limited nuclear weapons stockpiles. It was signed on 18 June 1979, but Carter faced an uphill battle to secure its [[ratification]] by the [[United States Senate|US Senate]].{{sfn|Doyle|2018|p=6}} MIRV technology had proved to be a major loophole in the 1972 SALT I Agreement, which limited numbers of missiles but not warheads. During the SALT II negotiations the US had resisted Soviet proposals to include the British and French nuclear forces in the agreement, but there were concerns that supplying MIRV technology to the UK would be seen by the Soviets as violating the spirit of the non-circumvention clause in SALT II.{{sfn|Doyle|2017a|pp=479–481}}

Callaghan was succeeded by [[Margaret Thatcher]] after the [[1979 United Kingdom general election|general election]] on 3 May 1979,{{sfn|Stoddart|2014|p=112}} and she discussed the issue with Carter in October, who agreed to supply C-4, but he asked that the UK delay a formal request until December in order that he could get SALT II ratified beforehand.{{sfn|Doyle|2018|pp=8–9}} In the meantime, the MDA, without which the UK would not be able to access US nuclear weapons technology, was renewed for five more years on 5 December, and the MISC 7 [[United Kingdom cabinet committee|cabinet committee]] formally approved the decision to purchase C-4 the following day.{{refn|group=note|In the UK system, most of the day-to-day work of the cabinet is carried out by cabinet committees, rather than by the full cabinet. Each committee has its own area of responsibility, and their decisions are binding on the entire cabinet. Their membership and scope is determined by the Prime Minister.<ref name="cabinet-manual-2011">{{cite web |url=https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/60641/cabinet-manual.pdf |title=The Cabinet Manual: A Guide to Laws, Conventions and Rules on the Operation of Government |publisher=[[Cabinet Office]] |date=October 2011 |access-date=18 July 2018 |archive-date=27 June 2016 |archive-url=https://web.archive.org/web/20160627174857/https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/60641/cabinet-manual.pdf |url-status=live }}</ref> During the post-Second World War period, in addition to standing committees, there were ''ad hoc'' committees that were convened to handle a single issue. These were normally short-lived. Each was given a prefix of GEN (general) or MISC (miscellaneous) and a number in order of formation.<ref>{{cite web |url=http://www.nationalarchives.gov.uk/help-with-your-research/research-guides/cabinet-and-committees/#11-cabinet-records-of-the-post-war-period |title=Cabinet and its committees |publisher=[[The National Archives (United Kingdom)|The National Archives]] |access-date=16 September 2017 |archive-date=16 September 2017 |archive-url=https://web.archive.org/web/20170916095423/http://www.nationalarchives.gov.uk/help-with-your-research/research-guides/cabinet-and-committees/#11-cabinet-records-of-the-post-war-period |url-status=live }}</ref> }}{{sfn|Stoddart|2014|pp=133–135}}<ref name="1958 Agreement">{{cite web |url=http://www.nti.org/media/pdfs/56_4.pdf |title=Agreement between the Government of the United States of America and the Government of the United Kingdom of Great Britain and Northern Ireland for Cooperation on the uses of Atomic Energy for Mutual Defence Purposes |publisher=Nuclear Threat Initiative |access-date=1 June 2017 |archive-date=12 April 2015 |archive-url=https://web.archive.org/web/20150412122614/http://www.nti.org/media/pdfs/56_4.pdf |url-status=live }}</ref> When Thatcher met with Carter again on 17 December, he still asked for more time,{{sfn|Stoddart|2014|pp=135–136}} but the [[Soviet invasion of Afghanistan]] on 24 December ended all hope of Senate ratification of SALT II, clearing the way for the sale to proceed.{{sfn|Doyle|2017a|pp=479–481}}

The British government hoped that Trident could be secured on the same terms as Polaris, but when its chief negotiator, [[Robert Wade-Gery]], sat down with his American counterpart, [[David L. Aaron]], in March 1980, he found this was not the case. Instead of the 5 per cent levy in recognition of US research and development (R&D) costs agreed to in the Polaris Sales Agreement, a 1976 law now required a ''pro rata'' fixed fee payment; the levy would have been approximately $100&nbsp;million, however the fixed fee amounted to around $400&nbsp;million.{{sfn|Stoddart|2014|pp=136–141}}{{sfn|Doyle|2017a|pp=482–484}}

[[File:Thatcher - Reagan c872-9.jpg|thumb|left|upright|[[Margaret Thatcher]] and [[Ronald Reagan]] on 26 February 1981]]
The law could be waived if the President determined that it was in the interest of the US to do so, but for that the Carter administration wanted undertakings that the UK would raise defence spending by the same amount, or pay the cost of US forces manning [[Rapier (missile)|Rapier]] batteries and [[BGM-109G Ground Launched Cruise Missile|Ground Launched Cruise Missile]] (GLCM) sites in the UK. On 2 June 1980, Thatcher and the US Secretary of Defense, [[Harold Brown (Secretary of Defense)|Harold Brown]], agreed to $2.5&nbsp;billion for the C-4 missile system, plus a 5 per cent R&D levy, British personnel for the Rapier batteries, and an expansion of the US base on [[Diego Garcia]], which had assumed great importance since the Soviet invasion of Afghanistan.{{sfn|Stoddart|2014|pp=136–141}}{{sfn|Doyle|2017a|pp=482–484}} The [[Secretary of State for Defence]], [[Francis Pym]], informed Cabinet of the decision to purchase Trident on 15 July 1980, and announced it in the [[House of Commons of the United Kingdom|House of Commons]] later that day.{{sfn|Stoddart|2014|p=143}} The agreement was effected by amending the Polaris Sales Agreement, changing "Polaris" to "Trident".{{sfn|Stoddart|2014|p=147}}

However, on 4 November 1980, [[Ronald Reagan]] was elected president. Part of his election platform was to modernise the US strategic nuclear forces. On 24 August 1981, the Reagan administration informed the British government of its intention to upgrade its Trident to the new [[UGM-133 Trident II|Trident II D-5 missile]] by 1989, and indicated that it was willing to sell it to the UK.{{sfn|Doyle|2017a|pp=484–485}}{{sfn|Doyle|2018|p=11}} Despite the name, the D-5 was not an improved version of the C-4, but a completely new missile.{{sfn|Doyle|2018|p=11}} Its purchase had already been considered in the Duff-Mason report, but had been rejected, as its additional capability—the extended range from {{convert|4000|to|6000|nmi|km}}—was not required by the UK, and it was more expensive. Exactly how much more expensive was uncertain, as it was still under development.{{sfn|Stoddart|2014|p=147}}{{sfn|Doyle|2017b|pp=870–871}} At the same time, the British government was well aware of the costs of not having the same hardware as the US. Nor did the Reagan administration promise to sell D-5 on the same terms as the C-4.{{sfn|Doyle|2017a|pp=484–485}} To pay for Trident, the British government announced deep cuts to other defence spending on 25 June 1981.{{sfn|Doyle|2017b|p=873}}

Negotiations commenced on 8 February, with the British team again led by Wade-Gery. The Americans were disturbed at the proposed British defence cuts, and pressed for an undertaking that the [[aircraft carrier]] {{HMS|Invincible|R05|6}} be retained in service, which they felt was necessary to avert trouble over the [[Belizean–Guatemalan territorial dispute]]. They accepted a counter-offer that Britain would retain the two [[landing platform dock]] ships, {{HMS|Fearless|L10|6}} and {{HMS|Intrepid|L11|2}}, for which the Americans reduced the R&D charge.{{sfn|Doyle|2017a|pp=486–487}} Under the agreement, the UK would purchase 65 Trident II D-5 missiles that would operate as part of a shared pool<ref name="Parliamentary written answers">{{cite web | url=https://www.publications.parliament.uk/pa/cm200506/cmhansrd/vo051027/text/51027w14.htm | title=Written Answers to Questions | work=Hansard | date=27 October 2005 | access-date=22 May 2017 | archive-date=28 October 2016 | archive-url=https://web.archive.org/web/20161028051219/http://www.publications.parliament.uk/pa/cm200506/cmhansrd/vo051027/text/51027w14.htm | url-status=live }}</ref> of weapons based at [[Naval Submarine Base Kings Bay]] in the US. The US would maintain and support the missiles, while the UK would manufacture its own submarines and warheads to go on the missiles.<ref name="Select Committee Eighth Report" /> The warheads and missiles would be mated in the UK. This was projected to save about £500&nbsp;million over eight years at Coulport, while the Americans spent $70&nbsp;million upgrading the facilities at Kings Bay. The sale agreement was formally signed on 19 October 1982 by the [[British Ambassador to the United States]], Sir [[Oliver Wright (diplomat)|Oliver Wright]], and the [[United States Secretary of State|US Secretary of State]], [[George Shultz]].{{sfn|Stoddart|2014|pp=197–199}}

The Trident programme was projected to cost £5&nbsp;billion, including the four submarines, the missiles, new facilities at Coulport and Faslane and the contribution to Trident II D-5 R&D. It was expected to absorb 5 per cent of the defence budget.<ref name="Guardian July 1980">{{cite news | url=http://century.guardian.co.uk/1980-1989/Story/0,,108170,00.html | title=£5&nbsp;billion Trident deal is agreed | newspaper=The Guardian | date=16 July 1980 | access-date=2 June 2012 | last=Fairhall | first=David | archive-date=6 August 2013 | archive-url=https://web.archive.org/web/20130806185353/http://century.guardian.co.uk/1980-1989/Story/0,,108170,00.html | url-status=live }}</ref> As with Polaris, the option for a fifth submarine (allowing two to be on patrol at all times) was discussed, but ultimately rejected.{{sfn|Stoddart|2014|pp=162–163}} Thatcher's popularity soared as a result of the British victory in the [[Falklands War]],<ref>{{cite news |url=https://www.theguardian.com/politics/2013/apr/09/margaret-thatcher-falklands-gamble |title=How Margaret Thatcher's Falklands gamble paid off |newspaper=The Guardian |access-date=12 July 2018 |first=Simon |last=Jenkins |date=9 April 2013 |archive-date=12 June 2018 |archive-url=https://web.archive.org/web/20180612163309/https://www.theguardian.com/politics/2013/apr/09/margaret-thatcher-falklands-gamble |url-status=live }}</ref> in which the ships that the Americans had insisted be retained played a crucial part.{{sfn|Grove|1987|pp=381–384}} Trident's future was secured the following year when the Conservative Party won the [[1983 United Kingdom general election|1983 general election]], defeating a Labour Party that had pledged to cancel Trident.<ref name="BBC Politics 1997">{{cite news | url=https://www.bbc.co.uk/news/special/politics97/background/pastelec/ge83.shtml | title=Politics 97 | work=BBC News | date=9 June 1983 | access-date=20 June 2018 | archive-date=6 April 2018 | archive-url=https://web.archive.org/web/20180406022756/http://www.bbc.co.uk/news/special/politics97/background/pastelec/ge83.shtml | url-status=live }}</ref> The first Trident boat, {{HMS|Vanguard|S28|6}} was ordered on 30 April 1986. In view of the Labour Party's continued opposition to Trident, [[Vickers Shipbuilding and Engineering|Vickers]] insisted that the contract include substantial compensation in the event of cancellation.{{sfn|Grove|1987|p=394}}

==UK's Nuclear Policies==
[[File:DASO Trident missile test firing on-board HMS Vigilant MOD 45159461.jpg|thumb|right|upright|alt=Photograph of a hand holding a pistol grip; the grip has a red trigger button and a coiled cable connected to its base.|The training trigger used to launch a simulated Trident missile on {{HMS|Vigilant|S30|6}}]]

===Cold War===
The Trident programme was initiated during the [[Cold War]], and it was designed to provide an ongoing independently controlled [[Deterrence theory|deterrent]] against major threats to the security of the UK and its NATO allies, including threats posed by non-nuclear weapons.<ref name="Future Deterrent">{{cite web | url=http://www.margaretthatcher.org/document/6AC6FE79AE5E485DB3A2B579B6AE0654.pdf | title=The Future United Kingdom Strategic Deterrent Force | publisher=The Defence Council | date=July 1980 | access-date=17 May 2012}}</ref>

To provide an effective deterrent, the Trident system was intended to "pose a potential threat to key aspects of [[Soviet Union|Soviet]] state power" whilst being invulnerable to a surprise or [[pre-emptive nuclear strike]]. As with Polaris, Trident was owned and operated by the UK but committed to NATO and targeted in accordance with plans set out by the organisation's [[Supreme Allied Commander Europe]], who is traditionally a senior figure in the US military.{{sfn|Dombey|2007|pp=33–34}} Under the terms of the Polaris Sales Arrangement, the US does not have a veto on the use of British nuclear weapons, which the UK may launch independently,<ref>{{cite web |title=Ministry of Defence, reply to a request about the UK nuclear deterrent |publisher=National Archives |url=http://www.mod.uk/NR/rdonlyres/E2054A40-7833-48EF-991C-7F48E05B2C9D/0/nuclear190705.pdf |archive-url=http://webarchive.nationalarchives.gov.uk/20121026065214/http://www.mod.uk/NR/rdonlyres/E2054A40-7833-48EF-991C-7F48E05B2C9D/0/nuclear190705.pdf |url-status=dead |archive-date=26 October 2012 |access-date=24 March 2018}}</ref> but this would only occur if "supreme national interests" required it.{{sfn|Dombey|2007|pp=33–34}}

The final decision on firing the missiles is the responsibility of the prime minister, who, upon taking office, writes four identical [[letters of last resort]], one of which is locked in a safe on board each of the ''Vanguard''-class submarines. If contact with the UK is lost, the commanding officer of a submarine has to follow the instructions in the letter if they believe that the United Kingdom has suffered an overwhelming attack. Options include retaliating with nuclear weapons, not retaliating, putting the submarine under the command of an ally or acting as the captain deems appropriate. The exact content of the letters is never disclosed, and they are destroyed without being opened upon a new prime minister taking office.<ref>{{cite news |last=Bunkall |first=Alistair |url=https://news.sky.com/story/may-to-be-handed-keys-to-nuclear-red-button-10499943 |access-date=26 March 2018 |date=13 July 2016 |publisher=Sky News |title=May To Be Handed Keys To Nuclear Red Button |archive-date=26 March 2018 |archive-url=https://web.archive.org/web/20180326063920/https://news.sky.com/story/may-to-be-handed-keys-to-nuclear-red-button-10499943 |url-status=live }}</ref>

===Post-Cold War===
By the time of the first ''Vanguard'' patrol in December 1994, the Soviet Union no longer existed, and the government adjusted its nuclear policy in the following years.<ref name="Select Committee Eighth Report" /> Trident's missiles were "detargetted" in 1994 ahead of ''Vanguard''{{'}}s maiden voyage.<ref>[https://www.theyworkforyou.com/wrans/?id=2005-07-11.9805.h Trident] {{Webarchive|url=https://web.archive.org/web/20051110181739/http://theyworkforyou.com/wrans/?id=2005-07-11.9805.h |date=10 November 2005 }}, [[Hansard]], 11 July 2005, Column 662W</ref> The warheads are not aimed at specific targets but await co-ordinates that can be programmed into their computers and fired with several days' notice.<ref name="modfeb16"/><ref name="Select Committee Eighth Report"/>

Under the terms of the 1987 [[Intermediate-Range Nuclear Forces Treaty]] with the Soviet Union, the US withdrew its surface naval nuclear weapons and short-range nuclear forces. The GLCMs were withdrawn from the UK in 1991,{{sfn|Ritchie|2014|pp=14–16}} and the Polaris submarine base at Holy Loch was closed in 1992.{{sfn|Chalmers|1999|p=63}} The last US warheads in British service under [[Project E]], the [[B57 nuclear bomb|B57 nuclear depth bomb]]s and the [[Lance missile]]s and [[W48]] nuclear artillery shells used by the [[British Army of the Rhine]], were withdrawn in July 1992.{{sfn|Ritchie|2014|pp=14–16}}  The British Conservative government followed suit. The deployment of ships carrying nuclear weapons caused embarrassment during the Falklands War, and in the aftermath it was decided to stockpile them ashore in peacetime.{{sfn|Grove|1987|p=384}} The nuclear depth bombs were withdrawn from service in 1992,<ref>{{cite web |url=http://www.nuclear-weapons.info/o.htm#OR.1178 |first=Brian |last=Burnell |title=Nuclear Weapons: A Guide to British Nuclear Weapons Projects |website=nuclear-weapons.info |access-date=13 July 2018 |archive-date=13 July 2018 |archive-url=https://web.archive.org/web/20180713012703/http://www.nuclear-weapons.info/o.htm#OR.1178 |url-status=live }}</ref><ref>{{cite news |newspaper=The Guardian |title=Falklands warships carried nuclear weapons, MoD admits |first1=Rob |last1=Evans |first2=David |last2=Leigh |date=7 December 2003 |url=https://www.theguardian.com/politics/2003/dec/06/military.freedomofinformation |access-date=13 July 2018 |archive-date=13 July 2018 |archive-url=https://web.archive.org/web/20180713012533/https://www.theguardian.com/politics/2003/dec/06/military.freedomofinformation |url-status=live }}</ref> followed by the [[WE.177]] free-fall bombs used by the Royal Navy and RAF on 31 March 1998.<ref>{{cite web |url=https://www.iwm.org.uk/collections/item/object/30021738 |title=WE 177 Type B (950lb), Training |publisher=Imperial War Museums |access-date=13 July 2018 |archive-date=13 July 2018 |archive-url=https://web.archive.org/web/20180713012344/https://www.iwm.org.uk/collections/item/object/30021738 |url-status=live }}</ref>  This left Trident as Britain's sole nuclear weapons system.<ref name="Select Committee Eighth Report" />
   
Although Trident was designed as a strategic deterrent, the end of the Cold War led the British government to conclude that a [[Nuclear warfare#Sub-strategic use|sub-strategic]]—but not [[Tactical nuclear weapon|tactical]]—role was required, with Trident missiles assuming the role formerly handled by the RAF's WE.177 bombs.{{sfn|Chalmers|1999|p=65}} The [[Front Line First|1994 Defence White Paper]] stated: "We also need the capability to undertake nuclear action on a more limited scale in order to ... halt aggression without inevitably triggering strategic nuclear exchanges". A later statement read: "We also intend to exploit the flexibility of Trident to provide the vehicle for both sub-strategic and strategic elements of our deterrent … as an insurance against potential adverse trends in the international situation".{{sfn|Larkin|1989|p=77}} On 19 March 1998, the Defence Secretary, [[George Robertson, Baron Robertson of Port Ellen|George Robertson]], was asked to provide a statement "on the development of a lower-yield variant of the Trident warhead for the sub-strategic role". He replied, "the UK has some flexibility in the choice of yield for the warheads on its Trident missiles".<ref name="Greenpeace written evidence">{{cite web|url=https://publications.parliament.uk/pa/cm200506/cmselect/cmdfence/986/986we12.htm|title=Annex A: Making Trident more usable and more threatening|work=Select Committee on Defence Written Evidence|publisher=House of Commons|date=June 2006|access-date=2 June 2012|archive-date=29 May 2012|archive-url=https://web.archive.org/web/20120529103319/http://www.publications.parliament.uk/pa/cm200506/cmselect/cmdfence/986/986we12.htm|url-status=live}}</ref>

The UK has not declared a [[no first use]] policy regarding launching a nuclear attack; former British defence secretary [[Geoff Hoon]] stated in 2002 and 2003 that the UK would be willing to attack rogue states with them if nuclear weapons were used against British troops.<ref>{{Cite news|url=http://news.bbc.co.uk/1/hi/uk_politics/1883258.stm  |title=BBC News&nbsp;— UK 'prepared to use nuclear weapons' |access-date=14 September 2007 |date= 20 March 2002<!--, 14:49 GMT--> |archive-url = https://web.archive.org/web/20021020052015/http://news.bbc.co.uk/1/hi/uk_politics/1883258.stm |archive-date = 20 October 2002}}</ref><ref>{{Cite news |url=http://news.bbc.co.uk/2/hi/uk_news/politics/2717939.stm |date=2 February 2003<!--, 19:25 GMT --> |title=BBC NEWS&nbsp;— UK restates nuclear threat |access-date=14 September 2007 |work=BBC News |archive-date=18 November 2018 |archive-url=https://web.archive.org/web/20181118165518/http://news.bbc.co.uk/2/hi/uk_news/politics/2717939.stm |url-status=live }}</ref> In April 2017 Defence Secretary [[Michael Fallon]] confirmed that the UK would use nuclear weapons in a "[[Pre-emptive nuclear strike|pre-emptive initial strike]]" in "the most extreme circumstances".<ref name=independent-20170424>{{cite news |url=https://www.independent.co.uk/news/uk/politics/theresa-may-nuclear-weapons-first-strike-michael-fallon-general-election-jeremy-corbyn-trident-a7698621.html |title=Theresa May would fire UK's nuclear weapons as a 'first strike', says Defence Secretary Michael Fallon |first=Rob |last=Merrick |newspaper=The Independent |date=24 April 2017 |access-date=24 April 2017 |archive-date=25 April 2017 |archive-url=https://web.archive.org/web/20170425031826/http://www.independent.co.uk/news/uk/politics/theresa-may-nuclear-weapons-first-strike-michael-fallon-general-election-jeremy-corbyn-trident-a7698621.html |url-status=dead }}</ref> Fallon stated in a parliamentary answer that the UK has neither a 'first use' or 'no first use' in its nuclear weapon policy so that its adversaries would not know when the UK would launch nuclear strikes.<ref>{{cite news |url=https://www.parliament.uk/business/publications/written-questions-answers-statements/written-question/Commons/2017-09-05/8502/ |title=Nuclear Weapons:Written question - 8502 |first=Michael |last=Fallon |date=5 September 2017 |access-date=18 November 2018 |archive-date=18 November 2018 |archive-url=https://web.archive.org/web/20181118164850/https://www.parliament.uk/business/publications/written-questions-answers-statements/written-question/Commons/2017-09-05/8502/ |url-status=live }}</ref>

In March 2021, the UK suggested a shift in nuclear policy in its Integrated Defence Review, stating that the UK would reserve the right to use nuclear weapons in the face of [[Weapon of mass destruction|weapons of mass destruction]], which includes "emerging technologies that could have a considerable impact", including cyber technologies, to chemical or biological weapons.<ref name=":0">{{cite report |title=Global Britain in a Competitive Age: The Integrated Review of Security, Defence, Development and Foreign Policy |page=77 |url=https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/969402/The_Integrated_Review_of_Security__Defence__Development_and_Foreign_Policy.pdf |publisher=HM Government |date=March 2021 |isbn=978-1-5286-2453-4 |url-status=live |archive-url=https://web.archive.org/web/20210317082158/https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/969402/The_Integrated_Review_of_Security__Defence__Development_and_Foreign_Policy.pdf |archive-date=17 March 2021 }}</ref> This marks a shift from existing UK policy, in that nuclear weapons would only be launched against another nuclear power or in response to extreme chemical or biological threats.<ref>{{Cite web|date=16 March 2021|title=Defence review: UK could use Trident to counter cyber-attack|url=http://www.theguardian.com/politics/2021/mar/16/defence-review-uk-could-use-trident-to-counter-cyber-attack|access-date=17 March 2021|website=The Guardian|language=en|archive-date=17 March 2021|archive-url=https://web.archive.org/web/20210317003018/https://www.theguardian.com/politics/2021/mar/16/defence-review-uk-could-use-trident-to-counter-cyber-attack|url-status=live}}</ref> It did, however, stress that the UK would not use or threaten to use nuclear weapons against any non-nuclear weapon party to the [[Treaty on the Non-Proliferation of Nuclear Weapons|Treaty on the Non-Proliferation of Nuclear Weapons 1968]], but only if the state is not in "material breach" of the Treaty's obligations.<ref name=":0" /> The shift in language comes after the UK lifted the cap on the number of [[Trident (missile)|Trident]] nuclear warheads it can stockpile by 40% from 180 to 260 warheads "in recognition of the evolving security environment".<ref name=":1">{{Cite web|date=15 March 2021|title=Cap on Trident nuclear warhead stockpile to rise by more than 40%|url=http://www.theguardian.com/uk-news/2021/mar/15/cap-on-trident-nuclear-warhead-stockpile-to-rise-by-more-than-40|access-date=17 March 2021|website=The Guardian|language=en|archive-date=16 March 2021|archive-url=https://web.archive.org/web/20210316233735/https://www.theguardian.com/uk-news/2021/mar/15/cap-on-trident-nuclear-warhead-stockpile-to-rise-by-more-than-40|url-status=live}}</ref><ref name=":2">{{Cite news|title=UK to expand nuclear stockpile in post-Brexit security review|url=https://www.ft.com/content/9784be23-8472-4268-9ea8-f1c0f8e23a24|url-status=live|access-date=17 March 2021|newspaper=Financial Times|date=15 March 2021 |archive-date=16 March 2021|archive-url=https://web.archive.org/web/20210316175403/https://www.ft.com/content/9784be23-8472-4268-9ea8-f1c0f8e23a24}}</ref> The UK has also stated it would no longer declare how many deployable warheads it has in a new policy of deliberate ambiguity.<ref name=":1" /> The move is intended to cement the UK's status as a nuclear power and a US defence ally.<ref name=":2" /><ref>{{Cite news|date=2 March 2021|title=Replacing Trident could take the UK-US 'special relationship' to "new heights"|language=en-GB|work=BBC News|url=https://www.bbc.com/news/uk-56256173|access-date=17 March 2021|archive-date=7 March 2021|archive-url=https://web.archive.org/web/20210307083657/https://www.bbc.com/news/uk-56256173|url-status=live}}</ref> [[Leader of the Labour Party (UK)|Labour Party Leader]] [[Keir Starmer]], although supporting nuclear deterrence, criticised the new policy and questioned why Prime Minister [[Boris Johnson]] believed that increasing the stockpile was necessary.<ref>{{Cite web|date=16 March 2021|title=Keir Starmer accuses PM of breaking policy on nuclear disarmament|url=http://www.theguardian.com/politics/2021/mar/16/keir-starmer-accuses-pm-of-breaking-policy-on-nuclear-disarmament|access-date=17 March 2021|website=The Guardian|language=en|archive-date=17 March 2021|archive-url=https://web.archive.org/web/20210317004019/https://www.theguardian.com/politics/2021/mar/16/keir-starmer-accuses-pm-of-breaking-policy-on-nuclear-disarmament|url-status=live}}</ref><ref>{{Cite news|date=26 February 2021|title=Labour renews vow to keep nuclear weapons|language=en-GB|work=BBC News|url=https://www.bbc.com/news/uk-politics-56198972|access-date=17 March 2021|archive-date=6 March 2021|archive-url=https://web.archive.org/web/20210306124056/https://www.bbc.com/news/uk-politics-56198972|url-status=live}}</ref> [[Kate Hudson (activist)|Kate Hudson]] of the [[Campaign for Nuclear Disarmament]] warned against the start of a "new nuclear arms race".<ref name=":1" />

==Design, development and construction==
===''Vanguard''-class submarines===
{{Main|Vanguard-class submarine}}
[[File:HMS Vanguard MOD 45154434.jpg|thumb|left|{{HMS|Vanguard|S28|6}} leaves [[HMNB Clyde]] in Scotland.]]
Four ''Vanguard''-class submarines were designed and built at Barrow-in-Furness by Vickers Shipbuilding and Engineering, now [[BAE Systems Submarines]], the only shipbuilder in the UK with the facilities and expertise to build nuclear submarines. Even so, £62&nbsp;million worth of new shipbuilding and dock facilities were added for the project,{{sfn|Stoddart|2014|p=52}} with the [[Devonshire Dock Hall]] built specially for it.<ref name="DDH" /> The initial plan was to build new versions of the ''Resolution''-class, but in July 1981 the decision was taken to incorporate the new [[Rolls-Royce Marine Power Operations|Rolls-Royce]] [[PWR2]] [[pressurised water reactor]]. From the outset, the ''Vanguard'' submarines were designed with enlarged missile tubes able to accommodate the Trident II D-5. The missile compartment is based on the system used on the American {{sclass|Ohio|submarine|4}}, although with capacity for only 16 missiles, rather than the 24 on board an ''Ohio'' boat. The boats are significantly larger than the ''Resolution'' class, and were given names formerly associated with [[battleship]]s and aircraft carriers, befitting their status as [[capital ship]]s.{{sfn|Grove|1987|p=356}} An important consideration was the depth of the [[Walney Channel]], which connected Barrow to the [[Irish Sea]], which limited the [[Draft (hull)|draft]] to {{convert|27+1/2|ft}}, while the ''Ohio''-class boats had a draft of {{convert|33|ft}}.{{sfn|Stoddart|2014|p=52}} Each boat is {{convert|150|m}} long and {{convert|13|m}} in diameter, and carries a crew of 150 officers and ratings.<ref name="Fact sheet 4: Current system" />

The submarines use a tactical-information and weapons-control system called the [[Submarine Command System Next Generation]].<ref>{{cite web |title=No, Trident doesn't run on Windows XP |date=15 May 2017 |last=Allison |first=George |url=https://ukdefencejournal.org.uk/no-trident-doesnt-run-windows-xp/ |publisher=UK Defence Journal |access-date=23 May 2018 |archive-date=22 October 2017 |archive-url=https://web.archive.org/web/20171022105052/https://ukdefencejournal.org.uk/no-trident-doesnt-run-windows-xp/ |url-status=live }}</ref> This system was developed in collaboration with [[Microsoft]],<ref>{{cite web |url=https://blogs.msdn.microsoft.com/ukgovernment/2008/12/17/windows-for-submarines/ |date=17 December 2008 |title=Windows for Submarines |author=British government |publisher=Microsoft |access-date=23 May 2018 |archive-date=23 May 2018 |archive-url=https://web.archive.org/web/20180523051618/https://blogs.msdn.microsoft.com/ukgovernment/2008/12/17/windows-for-submarines/ |url-status=live }}</ref> and is based on the same technology as [[Windows XP]], which led the media to give it the nickname "Windows for Submarines", with the [[UK Defence Journal]] fact checking group countering claims the vessels run on [[Windows XP]].<ref>{{cite news |url=https://www.theguardian.com/technology/2016/jan/16/trident-old-technology-brave-new-world-cyber-warfare |title='Trident is old technology': the brave new world of cyber warfare|date=16 January 2016|newspaper=The Guardian|access-date=18 May 2016}}</ref> In addition to the missile tubes, the submarines are fitted with four {{convert|21|in|mm|adj=on|0}} [[torpedo tube]]s and carry the [[Spearfish torpedo]],<ref>{{cite web| url=http://www.royal-navy.mod.uk/server/show/nav.2420| author=Royal Navy |title=Vanguard Class Ballistic Subs (SSBN)| access-date=18 June 2007| url-status=dead| archive-url=https://web.archive.org/web/20070623085113/http://www.royal-navy.mod.uk/server/show/nav.2420| archive-date=23 June 2007}}</ref> allowing them to engage submerged or surface targets at ranges up to {{convert|65|km|mi nmi}}. 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 need further re-fuelling.{{sfn|Saunders|2004|p=794}}

Thatcher laid the [[keel]] of the first boat, HMS ''Vanguard'', on 3 September 1986,<ref name="DDH">{{cite web |url=http://www.astuteclass.com/2011/09/05/ddh-celebrates-25th-birthday/ |archive-url=https://web.archive.org/web/20111116045412/http://www.astuteclass.com/2011/09/05/ddh-celebrates-25th-birthday/ |title=DDH celebrates 25th birthday |publisher=BAE Systems |date=5 September 2011 |archive-date=16 November 2011}}</ref> and it was commissioned on 14 August 1993. She was followed by her sisters, {{HMS|Victorious|S29|6}}, which was laid down on 3 December 1987 and commissioned on 7 January 1995; {{HMS|Vigilant|S30|6}}, which was laid down on 16 February 1991 and commissioned on 2 November 1996; and {{HMS|Vengeance|S31|6}}, which was laid down on 1 February 1993 and commissioned on 27 November 1999.{{sfn|Saunders|2004|p=794}} The first British Trident missile was test-fired from ''Vanguard'' on 26 May 1994, and she began her first patrol in December of that year. According to the Royal Navy, at least one submarine has always been on patrol ever since.<ref name="Royal Navy Vanguard">{{cite web | url=http://www.royalnavy.mod.uk/The-Fleet/Submarines/Ballistic-Submarines/Vanguard-Class | title=Vanguard Class | publisher=Royal Navy | access-date=2 June 2012 |archive-url=https://web.archive.org/web/20120604085804/http://www.royalnavy.mod.uk/The-Fleet/Submarines/Ballistic-Submarines/Vanguard-Class |archive-date=4 June 2012 }}</ref>

===Warheads===
[[File:Trident warheads.jpg|thumb|right|Models of the black warhead re-entry vehicles on a Trident missile at the [[National Museum of Nuclear Science & History]] in New Mexico]]
In British service, Trident II missiles are fitted with a thermonuclear warhead called Holbrook.<ref name = "BritCom">{{cite web| url =https://www.defensenews.com/global/europe/2020/02/25/britain-confirms-new-nuclear-warhead-project-after-us-officials-spill-the-beans/| title =Britain confirms new nuclear warhead project after US officials spill the beans| date =25 February 202| access-date =8 March 2020| archive-date =29 October 2020| archive-url =https://wayback.archive-it.org/all/20201029071418/https://www.defensenews.com/global/europe/2020/02/25/britain%2Dconfirms%2Dnew%2Dnuclear%2Dwarhead%2Dproject%2Dafter%2Dus%2Dofficials%2Dspill%2Dthe%2Dbeans/| url-status =live}}</ref> The warhead has a choice of two warhead yields<ref>{{cite AV media |people= |date=2005 |title=Keeping the peace: A history of AWE  |url=https://www.youtube.com/watch?v=sECZKRvW2F4 |access-date= |format= |time=15:35 |location= |publisher=Atomic Weapons Establishment |id= |isbn= |oclc= |quote= }}</ref> the highest of which is thought to be {{convert|100|ktonTNT|TJ}}, with a lower yield in the range of {{convert|0.3|to|10|ktonTNT|TJ}}.<ref name=NukeArch>{{cite web|url=https://nuclearweaponarchive.org/Uk/UKArsenalRecent.html|title=Britain's Nuclear Weapons; The Current British Arsenal|date=30 April 2001|website=The Nuclear Weapon Archive|publisher=Carey Sublette|access-date=29 January 2020|quote=The Trident warheads also offer multiple yields - probably 0.3 kt, 5-10 kt and 100 kt - by choosing to fire the unboosted primary, the boosted primary, or the entire "physics package".}}</ref> The UK government was sensitive to charges that the replacement of Polaris with Trident would involve an escalation in the numbers of British nuclear weapons. When the decision to purchase Trident II was announced in 1982, it was stressed that while American Trident boats carried 24 missiles with eight warheads each, a total of 192 warheads, British Trident boats would carry no more than 128 warheads—the same number as Polaris. In November 1993, the Secretary of State for Defence, [[Malcolm Rifkind]], announced that each boat would deploy no more than 96 warheads.{{sfn|Chalmers|1999|p=63}}  In 2010 this was reduced to a maximum of 40 warheads, split between eight missiles.<ref name="Fact sheet 4: Current system">{{cite web |publisher=Ministry of Defence |title=Fact sheet 4: Current system |series=The Future of the United Kingdom's Nuclear Deterrent |url=http://www.fas.org/nuke/guide/uk/doctrine/sdr06/FactSheet4.pdf |access-date=24 March 2018 |archive-date=9 March 2016 |archive-url=https://web.archive.org/web/20160309170425/http://fas.org/nuke/guide/uk/doctrine/sdr06/FactSheet4.pdf |url-status=live }}</ref><ref name="modfeb16"/> The consequent reduction in warhead production and refurbishment was estimated to save £22 million over a ten-year period.{{sfn|Chalmers|1999|p=64}} However in 2021 the Prime Minister [[Boris Johnson]] announced that the total number of warheads was being lifted from 180 to 260.<ref>{{cite news |title=Cap on Trident nuclear warhead stockpile to rise by more than 40% |first=Dan |last=Sabbagh |author-link=Dan Sabbagh |date= 16 March 2021 |newspaper=The Guardian |url=https://www.theguardian.com/uk-news/2021/mar/15/cap-on-trident-nuclear-warhead-stockpile-to-rise-by-more-than-40 |access-date=13 March 2023}}</ref>

The warheads are primarily constructed at [[Atomic Weapons Establishment|AWE Aldermaston]], with other parts being made at other AWE facilities such as [[Burghfield]].<ref>{{Cite web | url=http://www.awe.co.uk/what-we-do/our-proud-history/ | title=Our history | access-date=11 June 2018 | archive-url=https://web.archive.org/web/20180612140450/http://www.awe.co.uk/what-we-do/our-proud-history/ | archive-date=12 June 2018 | url-status=dead }}</ref> The British government insists the warhead is indigenously designed, but analysts including [[Hans M. Kristensen]] with the [[Federation of American Scientists]] believe that it is largely based on the US [[W76]] design.<ref name=BritCom/><ref>{{cite web|title=Britain's Next Nuclear era|url=https://fas.org/blogs/security/2006/12/britains_next_nuclear_era/|publisher=Federation of American Scientists|access-date=8 March 2020|date=7 December 2006|archive-date=4 June 2016|archive-url=https://web.archive.org/web/20160604151936/https://fas.org/blogs/security/2006/12/britains_next_nuclear_era/|url-status=live}}</ref> Under the 1958 US–UK Mutual Defence Agreement the UK is allowed to draw upon US warhead design information, but constructing and maintaining warheads for the Trident programme is the responsibility of AWE.<ref name="Select Committee Eighth Report"/> US President [[George H. W. Bush]] authorised the transfer of nuclear warhead components to the UK between 1991 and 1996.<ref>{{cite web |url=https://bush41library.tamu.edu/files/nsd/nsd61.pdf |title=National Security Directive 61 |publisher=The White House |date=2 July 1991 |access-date=9 May 2018 |archive-date=1 February 2017 |archive-url=https://web.archive.org/web/20170201141429/https://bush41library.tamu.edu/files/nsd/nsd61.pdf |url-status=live }}</ref> The first Holbrook warhead was finished in September 1992 with production probably ending in 1999.<ref name=NukeArch/> Each warhead is housed in a cone-shaped re-entry vehicle made in the US called the Mk 4 and is the same reentry vehicle used by the US Navy with its W76 warhead.<ref name="Greenpeace">{{cite web|url=https://publications.parliament.uk/pa/cm200506/cmselect/cmdfence/986/986we13.htm|title=UK's Trident system not truly independent|publisher=Greenpeace|access-date=1 March 2016|archive-date=3 March 2016|archive-url=https://web.archive.org/web/20160303185809/http://www.publications.parliament.uk/pa/cm200506/cmselect/cmdfence/986/986we13.htm|url-status=live}}</ref> This shell protects it from the high temperatures experienced upon re-entry into Earth's atmosphere.{{sfn|Mosher|1993|p=76}} The Trident warhead's fusing, arming and firing mechanisms are carefully designed so that it can only detonate after launch and ballistic deployment.<ref name="BBC News">{{cite news|url=http://news.bbc.co.uk/1/hi/programmes/newsnight/7097121.stm|title=Nuclear weapons security—MoD statement|work=BBC News|date=15 November 2007|access-date=1 March 2016|archive-date=20 August 2017|archive-url=https://web.archive.org/web/20170820075631/http://news.bbc.co.uk/1/hi/programmes/newsnight/7097121.stm|url-status=live}}</ref>

On 25 February 2020, the UK released a Written Statement outlining that the current UK nuclear warheads will be replaced and will match the US Trident SLBM and related systems.<ref>{{cite web |url=https://hansard.parliament.uk/commons/2020-02-25/debates/20022539000010/NuclearDeterrent |title=Nuclear Deterrent |author=<!--Not stated--> |date=25 February 2020 |website=hansard.parliament.uk |publisher=UK Hansard |access-date=26 February 2020 |archive-date=26 February 2020 |archive-url=https://web.archive.org/web/20200226115113/https://hansard.parliament.uk/commons/2020-02-25/debates/20022539000010/NuclearDeterrent |url-status=live }}</ref> Earlier, it was reported that Commander US Strategic Command, Admiral Charles Richard, mentioned in a Senate hearing that the UK was already working to replace its warheads, which would share technology with the future [[W93]] warhead.<ref>{{cite news |last=Doward |first=Jamie |date=22 February 2020 |title=Trident Pentagon reveals deal with Britain to replace Trident |url=https://www.theguardian.com/uk-news/2020/feb/22/pentagon-gaffe-reveals-uk-deal-replace-trident-nuclear-weapon |work=The Guardian |access-date=26 February 2020 |archive-date=25 February 2020 |archive-url=https://web.archive.org/web/20200225160554/https://www.theguardian.com/uk-news/2020/feb/22/pentagon-gaffe-reveals-uk-deal-replace-trident-nuclear-weapon |url-status=live }}</ref> 

In March 2024, the Ministry of Defence released a report which detailed, the replacement warhead would be designated as the A21/Mk7 and named Astraea''.'' The A21 Astraea warhead is to be a "sovereign design". It will be the first UK warhead to be deployed without live tests, relying on simulations and models from the AWE and EPURE, a joint UK-French facility.<ref>{{Cite web |date=25 March 2024 |title=Delivering the UK’s Nuclear Deterrent as a National Endeavour |url=https://assets.publishing.service.gov.uk/media/671b8641956d9b52e8c6d276/Defence_Nuclear_Enterprise_Command_Paper.pdf |url-status=live |archive-url=https://web.archive.org/web/20241209073517/https://assets.publishing.service.gov.uk/media/671b8641956d9b52e8c6d276/Defence_Nuclear_Enterprise_Command_Paper.pdf |archive-date=9 December 2024 |website=GOV.UK |publisher=Defence Nuclear Enterprise}}</ref>

{{As of|2016}}, the UK had a stockpile of 215 warheads, of which 120 are operationally available.<ref name="Stockpile">{{cite web|title=Nuclear Weapons: Who Has What at a Glance|url=https://www.armscontrol.org/factsheets/Nuclearweaponswhohaswhat|website=Arms Control Association|publisher=ACA|access-date=1 October 2016|archive-date=24 January 2018|archive-url=https://web.archive.org/web/20180124043430/https://www.armscontrol.org/factsheets/Nuclearweaponswhohaswhat|url-status=live}}</ref> In 2022 the UK Government  announced that "the UK will move to an overall nuclear weapon stockpile of no more than 260 warheads."<ref>{{cite web |title=Policy paper - Global Britain in a Competitive Age: the Integrated Review of Security, Defence, Development and Foreign Policy |date=2 July 2022 |publisher=UK Cabinet Office |url=https://www.gov.uk/government/publications/global-britain-in-a-competitive-age-the-integrated-review-of-security-defence-development-and-foreign-policy/global-britain-in-a-competitive-age-the-integrated-review-of-security-defence-development-and-foreign-policy#strengthening-security-and-defence-at-home-and-overseas |access-date=16 July 2022 }}</ref> British SSBNs on patrol carried a maximum of 40 warheads and 8 missiles.<ref name="SDSR2015">{{cite web|title=National Security Strategy and Strategic Defence and Security Review 2015|url=https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/478933/52309_Cm_9161_NSS_SD_Review_web_only.pdf|date=November 2015|publisher=HM Government|access-date=6 February 2021|archive-date=24 November 2015|archive-url=https://web.archive.org/web/20151124082813/https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/478933/52309_Cm_9161_NSS_SD_Review_web_only.pdf|url-status=live}}</ref> In 2011 it was reported that British warheads would receive the new Mk 4A reentry vehicles and some or all of the other upgrades that US W76 warheads were receiving in their W76-1 Life Extension Program.<ref>{{cite web |last=Kristensen |first=Hans |url=https://fas.org/blog/ssp/2011/04/britishw76-1.php |title=British Submarines to Receive Upgraded US Nuclear Warhead |publisher=Federation of American Scientists |access-date=1 April 2011 |archive-date=6 April 2011 |archive-url=https://web.archive.org/web/20110406231928/http://www.fas.org/blog/ssp/2011/04/britishw76-1.php |url-status=live }}</ref> Some reports suggested that British warheads would receive the same arming, fusing and firing system (AF&F) as the US W76-1.<ref>{{cite news |title=Trident more effective with US arming device, tests suggest |newspaper=[[The Guardian]] |first=Richard |last=Norton-Taylor |author-link=Richard Norton-Taylor |date=7 April 2011 |url=https://www.theguardian.com/uk/2011/apr/06/trident-us-arming-system-test|access-date=8 March 2020|archive-date=9 August 2020|archive-url=https://web.archive.org/web/20200809173248/https://www.theguardian.com/uk/2011/apr/06/trident-us-arming-system-test|url-status=live}}</ref> This new AF&F system, called the MC4700, would increase weapon lethality against hard targets such as missile silos and bunkers.<ref>{{cite web|title=How US nuclear force modernization is undermining strategic stability: The burst-height compensating super-fuze|date=March 2017 |url=https://thebulletin.org/2017/03/how-us-nuclear-force-modernization-is-undermining-strategic-stability-the-burst-height-compensating-super-fuze/|access-date=8 March 2020|archive-date=1 March 2020|archive-url=https://web.archive.org/web/20200301051403/https://thebulletin.org/2017/03/how-us-nuclear-force-modernization-is-undermining-strategic-stability-the-burst-height-compensating-super-fuze/|url-status=live}}</ref>
Due to the distance of {{convert|720|km|mi|abbr=on}} between AWE Aldermaston and the UK's nuclear weapon storage depot at RNAD Coulport, Holbrook (Trident) warheads are transported by road in [[Defence Nuclear Material Transport Operations|heavily armed convoys]] by [[Ministry of Defence Police]].<ref name="New Scientist November 2005">{{cite magazine | url=https://www.newscientist.com/article/mg18825253.000-if-a-nuclear-convoy-should-crash.html | title=If a nuclear convoy should crash... | magazine=New Scientist | date=12 November 2005 | access-date=20 May 2012 | last=Edwards | first=Robert | archive-date=10 October 2012 | archive-url=https://web.archive.org/web/20121010231925/http://www.newscientist.com/article/mg18825253.000-if-a-nuclear-convoy-should-crash.html | url-status=live }}</ref> According to a pressure group, between 2000 and 2016 the vehicles were involved in 180 incidents, ranging from delays and diversions because of accidents, protests, or bad weather, to a sudden loss of power in one of the lorries, which halted a convoy and caused a double lane closure and a [[traffic congestion|tailback]] on the [[M6 motorway]]. The group's analysis stated the incidents were more frequent in the years 2013–2015.<ref>{{cite news|url=https://www.theguardian.com/uk-news/2016/sep/21/uk-nuclear-weapons-convoys-have-had-180-mishaps-in-16-years|title=UK nuclear weapons convoys 'have had 180 mishaps in 16 years'|last=Evans|first=Rob|date=22 September 2016|newspaper=The Guardian|access-date=22 September 2016|archive-date=21 September 2016|archive-url=https://web.archive.org/web/20160921223913/https://www.theguardian.com/uk-news/2016/sep/21/uk-nuclear-weapons-convoys-have-had-180-mishaps-in-16-years|url-status=live}}</ref>

===Trident II D-5 missiles===
{{main|UGM-133 Trident II}}
[[File:Trident II missile image.jpg|thumb|left|Test launch of a Trident II missile]]
Trident II D-5 is a submarine-launched ballistic missile built by [[Lockheed Martin Space Systems]] in [[Sunnyvale, California]], and deployed by the US Navy and the Royal Navy.<ref>{{cite web |url=https://news.lockheedmartin.com/2015-11-10-U-S-Navys-Trident-II-D5-Missile-Achieves-New-Test-Flight-Reliability-Record |title=U.S. Navy's Trident II D5 Missile Achieves New Test Flight Reliability Record |date=10 November 2015 |publisher=Lockheed-Martin |access-date=18 July 2018 |archive-date=18 July 2018 |archive-url=https://web.archive.org/web/20180718030552/https://news.lockheedmartin.com/2015-11-10-U-S-Navys-Trident-II-D5-Missile-Achieves-New-Test-Flight-Reliability-Record |url-status=live }}</ref> The British government contributed five per cent of its research and development costs under the modified Polaris Sales Agreement. The development contract was issued in October 1983, and the first launch occurred in January 1987. The first submarine launch was attempted by {{USS|Tennessee|SSBN-734|6}} in March 1989. This attempt failed because the plume of water following the missile rose to a greater height than expected, resulting in water being in the nozzle when the motor ignited. Once the problem was understood, simple changes were quickly made, but the problem delayed the entry into service of Trident II until March 1990.<ref name="UGM-133">{{cite web|url=http://www.designation-systems.net/dusrm/m-133.html|title=UGM-133|last=Parsch|first=Andreas|publisher=Directory of US Military Rockets and Missiles|access-date=14 February 2009|archive-date=15 March 2011|archive-url=https://web.archive.org/web/20110315090113/http://www.designation-systems.net/dusrm/m-133.html|url-status=live}}</ref>

Trident II D-5 is more sophisticated than its predecessor, Trident I C-4, and has a greater payload capacity. All three stages of the Trident II D-5 are made of [[Carbon fiber reinforced polymer|graphite epoxy]], making the missile much lighter than its predecessor.{{sfn|Spinardi|1994|p=159}} The first test from a British ''Vanguard''-class submarine took place in 1994.<ref>{{cite web | url=https://news.lockheedmartin.com/2012-03-14-Lockheed-Martin-Built-Trident-II-D5-Missile-Achieves-137th-Successful-Test-Flight | title=Lockheed Martin-Built Trident II D5 Missile Achieves 137th Successful Test Flight | date=14 March 2012 | publisher=Lockheed-Martin | access-date=18 July 2018 | archive-date=18 July 2018 | archive-url=https://web.archive.org/web/20180718030604/https://news.lockheedmartin.com/2012-03-14-Lockheed-Martin-Built-Trident-II-D5-Missile-Achieves-137th-Successful-Test-Flight | url-status=live }}</ref> The missile is {{convert|13|m|ft|0}} long, weighs {{convert|58.5|t|lb}}, has a range of {{convert|11300|km|mi}}, a top speed of over {{convert|21600|km/h|mph|abbr=on}} (Mach 17.4) and a [[circular error probable]] (CEP) accuracy to within "a few feet".<ref name="bbctridentfacts">{{cite news|url=http://news.bbc.co.uk/1/hi/uk/4438392.stm|title=Trident missile factfile|work=BBC News|date=23 September 2009|access-date=1 March 2016|archive-date=31 July 2017|archive-url=https://web.archive.org/web/20170731145532/http://news.bbc.co.uk/1/hi/uk/4438392.stm|url-status=live}}</ref> It is guided using an [[inertial navigation system]] combined with a [[star tracker]], and is not dependent on the American-run [[Global Positioning System]] (GPS).<ref name="modfeb16"/>

The 1998 [[Strategic Defence Review]] announced that the number of missile bodies would be limited to the 58 already purchased or under order, and the Royal Navy would not receive the final seven missiles previously planned.<ref name="1998 Strategic Defence Review">{{cite web | url=http://www.mod.uk/NR/rdonlyres/65F3D7AC-4340-4119-93A2-20825848E50E/0/sdr1998_complete.pdf | title=Strategic Defence Review | publisher=Ministry of Defence | access-date=22 May 2017 |archive-url=http://webarchive.nationalarchives.gov.uk/20121026065214/www.mod.uk/NR/rdonlyres/65F3D7AC-4340-4119-93A2-20825848E50E/0/sdr1998_complete.pdf | archive-date=26 October 2012 }}</ref> This saved about £50 million.{{sfn|Chalmers|1999|p=64}} The UK missiles form a shared pool with the Atlantic squadron of the US Navy ''Ohio''-class SSBNs at Kings Bay. The pool is "co-mingled" and missiles are selected at random for loading on to either nation's submarines.<ref name=UKDJ2017/><ref>{{cite web|url=https://ukdjcdn-b4d.kxcdn.com/uploads/2014/07/UK-Nuclear-Deterrent-FOI-Response.pdf|title=Freedon of information request about the UK nuclear deterrent |date=19 July 2005|access-date=25 January 2017|publisher=Ministry of Defence|url-status=dead|archive-url=https://web.archive.org/web/20161030002309/https://ukdjcdn-b4d.kxcdn.com/uploads/2014/07/UK-Nuclear-Deterrent-FOI-Response.pdf|archive-date=30 October 2016}}</ref> The first Trident boat, HMS ''Vanguard'', collected a full load of 16 missiles in 1994, but ''Victorious'' collected only 12 in 1995, and ''Vigilant'', 14 in 1997, leaving the remaining missile tubes empty.{{sfn|Butler|Bromley|2001|p=10}}

By 1999, six missiles had been test fired, and another eight were earmarked for test firing.{{sfn|Chalmers|1999|p=73}} In June 2016, a Trident II D-5 missile "veered off in the wrong direction towards America" after being launched from ''Vengeance'' off the coast of Florida.<ref name=UKDJ2017>{{cite web|title=How serious was the Trident missile test failure?|url=https://ukdefencejournal.org.uk/serious-trident-missile-test-failure/|publisher=UK Defence Journal|access-date=24 January 2017|date=22 January 2017|archive-date=2 February 2017|archive-url=https://web.archive.org/web/20170202015319/https://ukdefencejournal.org.uk/serious-trident-missile-test-failure/|url-status=live}}</ref><ref>{{cite web |url=http://www.parliament.uk/business/committees/committees-a-z/commons-select/defence-committee/news-parliament-2015/trident-missile-testing/ |title=Admiral Lord West and Professor Michael Clarke questioned on Trident |publisher=UK Parliament |access-date=26 January 2017 |archive-date=2 February 2017 |archive-url=https://web.archive.org/web/20170202074808/http://www.parliament.uk/business/committees/committees-a-z/commons-select/defence-committee/news-parliament-2015/trident-missile-testing/ |url-status=live }}</ref> The incident was not revealed until January 2017; the ''Sunday Times'' reported that [[Downing Street]] had "covered up" the incident "just weeks before the crucial House of Commons vote on the future of the missile system."<ref>{{cite news |url=http://www.thetimes.co.uk/edition/news/no-10-covered-up-trident-missile-fiasco-hch3shsrn |title=No 10 covered up Trident missile fiasco |newspaper=The Times |date=22 January 2017 |access-date=26 January 2017 |archive-date=23 January 2017 |archive-url=https://web.archive.org/web/20170123045852/http://www.thetimes.co.uk/edition/news/no-10-covered-up-trident-missile-fiasco-hch3shsrn |url-status=live }}</ref> Subsequent media reports said this was at the request of the US.<ref>{{cite news |url=http://www.thetimes.co.uk/article/us-urged-britain-to-keep-trident-blunder-secret-knqkbdt5b |first1=Sam |last1=Coates |first2=Francis |last2=Elliott |title=US urged Britain to keep Trident blunder secret |newspaper=The Times |date=24 January 2017 |access-date=26 January 2017 |archive-date=24 January 2017 |archive-url=https://web.archive.org/web/20170124200946/http://www.thetimes.co.uk/article/us-urged-britain-to-keep-trident-blunder-secret-knqkbdt5b |url-status=live }}</ref> Successful Royal Navy test firings had occurred in 2000, 2005, 2009 and 2012. They are infrequent due to the missile's £17&nbsp;million cost.<ref>{{cite news |newspaper=The Guardian |first=Ewen |last=Askell |title=How did the Trident test fail and what did Theresa May know? |url=https://www.theguardian.com/uk-news/2017/jan/23/how-did-the-trident-test-fail-and-what-did-theresa-may-know |date=24 January 2017 |access-date=26 January 2017 |archive-date=25 January 2017 |archive-url=https://web.archive.org/web/20170125215011/https://www.theguardian.com/uk-news/2017/jan/23/how-did-the-trident-test-fail-and-what-did-theresa-may-know |url-status=live }}</ref> By August 2016 there had been 161 successful test firings of the Trident II D-5 missile since 1989, the most recent being from {{USS|Maryland|SSBN-738|6}} in August 2016.<ref>{{cite web |url=http://www.lockheedmartin.co.uk/us/news/press-releases/2016/september/ssc-space-trdent.html |title=Successful Trident II D5 Missile Flight Test Supports Navy Submarine Certification for Strategic Patrol |publisher=Lockheed Martin |date=13 September 2016 |access-date=26 January 2017 |url-status=dead |archive-url=https://web.archive.org/web/20170126023501/http://www.lockheedmartin.co.uk/us/news/press-releases/2016/september/ssc-space-trdent.html |archive-date=26 January 2017  }}</ref>  

A second failure occurred at the next launch in January 2024. There was a reported failure of the first stage, with the missile landing into the ocean, next to the submarine soon after launch. It was claimed the fault was specific to the test and would have been unlikely to occur when using a real nuclear warhead, according to the [[Ministry of Defence (United Kingdom)|Ministry of Defence]].<ref>{{Cite web |last=Kent |first=Lauren |date=2024-02-21 |title=UK nuclear missile test fails for second time in eight years |url=https://www.cnn.com/2024/02/21/europe/trident-missile-uk-failure-intl/index.html |access-date=2024-02-25 |website=CNN |language=en}}</ref> The failed test attracted ridicule from global media.<ref>{{Cite news |last=Bowden |first=George |date=22 February 2024 |title=How Russian media mocked UK's Trident missile failure |url=https://www.bbc.co.uk/news/world-68369556 |work=[[BBC News]]}}</ref> 5 test flights have been failures since 1989.<ref>{{cite news |last1=McCann |first1=Kate |last2=Dominiczak |first2=Peter |last3=Swinford |first3=Steven |date=23 January 2017 |title=US Trident failure claims contradict Michael Fallon |url=https://www.telegraph.co.uk/news/2017/01/23/theresa-may-briefed-trident-missile-test-allegedly-misfired2/ |url-status=live |archive-url=https://web.archive.org/web/20170125175326/http://www.telegraph.co.uk/news/2017/01/23/theresa-may-briefed-trident-missile-test-allegedly-misfired2/ |archive-date=25 January 2017 |access-date=26 January 2017 |newspaper=The Daily Telegraph}}</ref>

===Cost===
In the 1990s, the total acquisition cost of the Trident programme was £9.8&nbsp;billion, about 38 per cent of which was incurred in the US. In 2005–06, annual expenditure for the running and capital costs was estimated at between £1.2&nbsp;billion and £1.7&nbsp;billion and was estimated to rise to £2bn to £2.2&nbsp;billion in 2007–08, including Atomic Weapons Establishment costs. Since Trident became operational in 1994, annual expenditure has ranged between 3 and 4.5 per cent of the annual defence budget, and was projected to increase to 5.5 per cent of the defence budget by 2007–08.<ref name=HoClib-rp06-53>{{cite report|url=http://www.parliament.uk/commons/lib/research/rp2006/rp06-053.pdf|title=The Future of the British Nuclear Deterrent|version=Research paper 06/53|date=3 November 2006|publisher=House of Commons Library|access-date=15 March 2007|url-status=dead|archive-url=https://web.archive.org/web/20061121003637/http://www.parliament.uk/commons/lib/research/rp2006/rp06-053.pdf|archive-date=21 November 2006}}</ref>{{sfn|National Audit Office|1987|pp=14,18}}  An important factor in the cost was the [[exchange rate]] between the dollar and the pound, which declined from $2.36 in September 1980 to $1.78 in March 1982.{{sfn|Grove|1987|p=356}}

==Operation==
[[File:Vanguard at Faslane 03.jpg|thumb|right|{{HMS|Vanguard|S28|6}} at Faslane]]

===Patrols===
The principle of Trident's operation is known as Continuous At-Sea Deterrence (CASD), which means that at least one submarine is always on patrol.<ref>{{cite web|url=http://www.awe.co.uk/what-we-do/supporting-the-uks-deterrent/|publisher=AWE|title=Supporting the UK's deterrent|access-date=1 March 2016|archive-date=5 March 2016|archive-url=https://web.archive.org/web/20160305093359/http://www.awe.co.uk/what-we-do/supporting-the-uks-deterrent/|url-status=live}}</ref> Another submarine is usually undergoing maintenance and the remaining two are in port or on training exercises. During a patrol, the submarine is required to [[radio silence|remain silent]] and is allowed to make contact with the UK only in an emergency. It navigates using mapped [[contour lines]] of the ocean floor and patrols a series of planned "boxes" measuring several thousand square miles. A {{convert|1000|m|ft|adj=mid|-long}} aerial trails on the surface behind the submarine to pick up incoming messages.{{Citation needed|date=February 2021}} Most of the 150 crew never know where they are or where they have been.<ref name="Bilton">{{cite news|title=Dive bombers|author=Michael Bilton|newspaper=The Sunday Times Magazine|date=20 January 2008|url=https://www.thetimes.co.uk/article/dive-bombers-s7llt2vjckq|access-date=18 July 2018|archive-date=18 July 2018|archive-url=https://web.archive.org/web/20180718001520/https://www.thetimes.co.uk/article/dive-bombers-s7llt2vjckq|url-status=live}}</ref> The 350th patrol commenced on 29 September 2017.<ref>{{cite news|title=UK marks 350th UK deterrent patrol|url=https://www.gov.uk/government/news/uk-marks-350th-uk-deterrent-patrol|access-date=3 October 2017|publisher=Ministry of Defence|date=29 September 2017|archive-date=3 October 2017|archive-url=https://web.archive.org/web/20171003124526/https://www.gov.uk/government/news/uk-marks-350th-uk-deterrent-patrol|url-status=live}}</ref><ref>{{cite news|title=Sir Michael Fallon defends nuclear deterrent amid heightened North Korea threat|url=http://news.sky.com/story/sir-michael-fallon-defends-nuclear-deterrent-amid-heightened-north-korea-threat-11059332|access-date=3 October 2017|publisher=Sky News|date=29 September 2018|archive-date=3 October 2017|archive-url=https://web.archive.org/web/20171003124918/http://news.sky.com/story/sir-michael-fallon-defends-nuclear-deterrent-amid-heightened-north-korea-threat-11059332|url-status=live}}</ref> On 15 November 2018, a reception was held at Westminster to mark 50 years of CASD.<ref>{{cite news |title=Special reception in Westminster marks 50 years of continuous sea deterrent |url=https://www.nwemail.co.uk/news/17226076.special-reception-in-westminster-marks-50-years-of-continuous-sea-deterrent/ |access-date=18 November 2018 |newspaper=The Mail |first=Tom |last=Murphy |date=15 November 2018 |archive-date=18 November 2018 |archive-url=https://web.archive.org/web/20181118122837/https://www.nwemail.co.uk/news/17226076.special-reception-in-westminster-marks-50-years-of-continuous-sea-deterrent/ |url-status=live }}</ref>

===Command and control===
Only the prime minister or a designated survivor can authorise the missiles to be fired.<ref name="parliament.uk">{{cite web|url=https://www.parliament.uk/business/publications/written-questions-answers-statements/written-question/Lords/2018-11-05/HL11260/|title=Ministry of Defence Nuclear Submarines|date=5 November 2018|access-date=18 November 2018|archive-date=18 November 2018|archive-url=https://web.archive.org/web/20181118122951/https://www.parliament.uk/business/publications/written-questions-answers-statements/written-question/Lords/2018-11-05/HL11260/|url-status=live}}</ref> These orders would likely be issued from the [[Military citadels under London#Pindar|Pindar]] command bunker under [[Whitehall]] in central London. From there, the order would be relayed to the Commander, [[Joint Task Force|Task Force]] 345 (CTF 345) operations room at the [[Northwood Headquarters]] facility in [[Hertfordshire]], the only facility allowed to communicate with the ''Vanguard'' commander on patrol.<ref>{{cite news |newspaper=The Telegraph |title=What would really happen if Britain came under nuclear attack? |first=Guy |last=Kelly |date=4 September 2017 |url=https://www.telegraph.co.uk/men/the-filter/would-really-happen-britain-came-nuclear-attack/ |access-date=28 March 2018 |archive-date=29 March 2018 |archive-url=https://web.archive.org/web/20180329060646/https://www.telegraph.co.uk/men/the-filter/would-really-happen-britain-came-nuclear-attack/ |url-status=live }}</ref> Communications are relayed via IP over VLF from a transmitter site at [[Skelton Transmitting Station|Skelton]] near Penrith.<ref>{{Cite web|date=June 2017|title=Hacking UK Trident|url=https://www.basicint.org/wp-content/uploads/2018/06/HACKING_UK_TRIDENT.pdf|access-date=26 August 2020|website=British American Security Information Council (BASIC)|page=26|archive-date=11 January 2021|archive-url=https://web.archive.org/web/20210111225336/https://basicint.org/wp-content/uploads/2018/06/HACKING_UK_TRIDENT.pdf|url-status=live}}</ref>   Two personnel are required to authenticate each stage of the process before launching, with the submarine commander only able to activate the firing trigger after two safes have been opened with keys held by the ship's executive and [[Engineer Officer (Royal Navy)#Weapon Engineer|weapon engineer]] officers.<ref>{{cite news |newspaper=The Telegraph |title=Trident: The man with the nuclear button who would fire Britain's missiles |first=Ben |last=Farmer |date=21 January 2016 |url=https://www.telegraph.co.uk/news/uknews/defence/12113193/Trident-The-man-with-the-nuclear-button-who-would-fire-Britains-missiles.html |access-date=28 March 2018 |archive-date=28 March 2018 |archive-url=https://web.archive.org/web/20180328104102/https://www.telegraph.co.uk/news/uknews/defence/12113193/Trident-The-man-with-the-nuclear-button-who-would-fire-Britains-missiles.html |url-status=live }}</ref> A parliamentary answer states that commanding officers of Royal Navy ballistic submarines receive training in the 'Law Of Armed Conflict'.<ref name="parliament.uk"/>

[[File:HMS Vigilant alongside Faslane Naval Base. MOD 45147682.jpg|thumb|left|{{HMS|Vigilant|S30|6}} alongside No. 10 berth at HM Naval Base (HMNB) Clyde in October 2007]]

===Bases===
Trident is based at HMNB Clyde on the west coast of Scotland. The base consists of two facilities&nbsp;— Faslane Naval Base on [[Gare Loch]] near [[Helensburgh]], and an ordnance depot with 16 concrete bunkers set into a hillside at Coulport, {{convert|4|km|mi|abbr=on|1}} to the west. Faslane was constructed and first used as a base during the Second World War.  This location was chosen as the base for nuclear-armed submarines at the height of the Cold War because of its position close to the deep and easily navigable Firth of Clyde. It provides for rapid and stealthy access through the [[North Channel (Great Britain and Ireland)|North Channel]] to the patrolling areas in the North Atlantic, and through the [[GIUK gap]] between Iceland and Scotland to the [[Norwegian Sea]]. Also based there are {{sclass|Astute|submarine|0}} nuclear-powered [[fleet submarine]]s (SSNs).{{sfn|Nailor|1988|pp=91–96}}<ref>{{cite news |publisher=BBC |title=What do we know about Faslane, the home of Trident nuclear weapons? |first=Stuart |last=Nicolson |url=https://www.bbc.com/news/uk-scotland-34106546 |access-date=28 March 2018 |archive-date=9 February 2018 |archive-url=https://web.archive.org/web/20180209145307/http://www.bbc.com/news/uk-scotland-34106546 |url-status=live }}</ref> RNAD Coulport is used to store the nuclear warheads and has docking facilities where they are loaded onto submarines before going on patrol and unloaded when they return to the base.<ref>{{cite web |url=http://www.savetheroyalnavy.org/why-relocating-trident-away-from-scotland-is-virtually-impossible/ |title=Why relocating Trident away from Scotland is virtually impossible |publisher=Save The Royal Navy |date=22 July 2016 |access-date=28 March 2018 |archive-date=28 March 2018 |archive-url=https://web.archive.org/web/20180328110823/http://www.savetheroyalnavy.org/why-relocating-trident-away-from-scotland-is-virtually-impossible/ |url-status=live }}</ref> Repair and refit of the ''Vanguard''-class submarines takes place at [[HMNB Devonport]] near [[Plymouth]], Devon.<ref>{{cite news |newspaper=The Herald |url=https://www.plymouthherald.co.uk/news/plymouth-news/devonport-dockyard-ordered-improve-safety-396138 |title=Devonport Dockyard ordered to improve safety by nuclear watchdog after 'several' incidents |first=Gayle |last=McDonald |date=29 August 2017 |access-date=28 March 2018 |archive-date=28 March 2018 |archive-url=https://web.archive.org/web/20180328103201/https://www.plymouthherald.co.uk/news/plymouth-news/devonport-dockyard-ordered-improve-safety-396138 |url-status=live }}</ref>

===Espionage===
According to senior RAF officers the retirement of the [[Hawker Siddeley Nimrod|Nimrod]] maritime patrol aircraft in 2011 gave Russia the potential to gain "valuable intelligence" on the country's nuclear deterrent. As a result, plans to buy [[Northrop Grumman MQ-4C Triton]] unmanned aerial vehicles were reportedly considered.<ref>{{cite news| title=UK to spend £600m on spy drones to protect Britain from Russian incursion| url=http://www.ibtimes.co.uk/uk-spend-600m-spy-drones-protect-britain-russian-incursion-1457448| date=20 July 2014| newspaper=International Business Times| access-date=19 June 2015| archive-date=19 June 2015| archive-url=https://web.archive.org/web/20150619163000/http://www.ibtimes.co.uk/uk-spend-600m-spy-drones-protect-britain-russian-incursion-1457448| url-status=live}}</ref><ref>{{cite news |last=Kaye |first=Yasmin |title=RAF cuts to Nimrod patrols allows Russians to spy on Trident submarines, warn experts |newspaper=International Business Times |url=http://www.ibtimes.co.uk/raf-cuts-nimrod-patrols-allows-russians-spy-trident-submarines-warn-experts-1503626 |date=30 May 2015 |access-date=19 June 2015 |archive-date=19 June 2015 |archive-url=https://web.archive.org/web/20150619174150/http://www.ibtimes.co.uk/raf-cuts-nimrod-patrols-allows-russians-spy-trident-submarines-warn-experts-1503626 |url-status=live }}</ref> The [[Strategic Defence and Security Review 2015]] announced that nine [[Boeing P-8 Poseidon]] maritime patrol aircraft would be purchased for the RAF.<ref name=SDSR2015/> They became operational on 3 April 2020.<ref name="P8IOC">{{cite news |title=RAF Declare Poseidon an Initial Operating Capability |url=https://www.raf.mod.uk/news/articles/raf-declare-poseidon-an-initial-operating-capability/ |access-date=7 November 2020 |agency=[[Royal Air Force]] |date=3 April 2020 |archive-date=2 November 2020 |archive-url=https://web.archive.org/web/20201102024915/https://www.raf.mod.uk/news/articles/raf-declare-poseidon-an-initial-operating-capability/ |url-status=live }}</ref>

==Opposition==
[[File:Stop Trident CND Demo February 27 2016 043 Piccadilly (16) (25336299995).jpg|thumb|Anti-Trident demonstrators in London, February 2016]]
The [[Campaign for Nuclear Disarmament]] (CND) was a national movement founded in the late 1950s, initially in opposition to nuclear testing. It reached its peak around 1960, by which time it had evolved into a broader movement calling for Britain to unilaterally give up nuclear weapons, withdraw from NATO, and end the basing of nuclear-armed aircraft in the UK. The end of atmospheric nuclear testing, internal squabbles, and activists focusing their energies on other causes led to a rapid decline, but it revived in the early 1980s in the wake of the Thatcher government's December 1979 decision to allow the deployment of GLCMs in the UK under the [[NATO Double-Track Decision]], and the announcement of the decision to purchase Trident in July 1980. Membership leapt from 3,000 in 1980 to 50,000 a year later, and rallies for unilateral nuclear disarmament in London in October 1981 and June 1982 attracted 250,000 marchers, the largest ever mass demonstrations in the UK up to that time.{{sfn|Bowie|Platt|1984|pp=63–70}}

The 1982 [[Labour Party Conference]] adopted a platform calling for the removal of the GLCMs, the scrapping of Polaris and the cancellation of Trident. This was reaffirmed by the 1986 conference. While the party was given little chance of winning the 1983 election in the aftermath of the Falklands War, polls had shown Labour ahead of the Conservatives in 1986 and 1987. In the wake of Labour's unsuccessful performance in the [[1987 United Kingdom general election|1987 election]], the Labour Party leader, [[Neil Kinnock]], despite his own unilateralist convictions, moved to drop the party's disarmament policy, which he saw as a contributing factor in its defeat.{{sfn|Scott|2012|pp=116-118}}<ref>{{cite news |publisher=BBC |url=https://www.bbc.co.uk/news/special/politics97/background/pastelec/ge83.shtml |title=Politics 97 |access-date=13 July 2018 |archive-date=6 April 2018 |archive-url=https://web.archive.org/web/20180406022756/http://www.bbc.co.uk/news/special/politics97/background/pastelec/ge83.shtml |url-status=live }}</ref> The party formally voted to do so in October 1989.{{sfn|Chalmers|1999|p=62}}

Pro-independence Scottish political parties—the [[Scottish National Party]] (SNP), [[Scottish Green Party]], [[Scottish Socialist Party]] (SSP) and [[Solidarity (Scotland)|Solidarity]]—are opposed to the basing of the Trident system close to Glasgow, Scotland's largest city.{{sfn|Ritchie|2016|pp=658–659}} Some members and ex-members of those parties, such as [[Tommy Sheridan]] and [[Lloyd Quinan]], have taken part in blockades of the base.<ref>{{cite news |newspaper=The Telegraph |title=Sheridan held again in Faslane protest |first=Tara |last=Womersley |date=23 October 2001 |url=https://www.telegraph.co.uk/news/uknews/1360222/Sheridan-held-again-in-Faslane-protest.html |access-date=5 May 2018 |archive-date=5 May 2018 |archive-url=https://web.archive.org/web/20180505204834/https://www.telegraph.co.uk/news/uknews/1360222/Sheridan-held-again-in-Faslane-protest.html |url-status=live }}</ref> For a major House of Commons vote in 2007, the majority of Scottish members of parliament (MPs) voted against upgrading the system, while a substantial majority of English and Welsh MPs voted in favour. The house backed plans to renew the programme by 409 votes to 161.<ref>{{cite news|url=http://news.bbc.co.uk/1/hi/scotland/6452275.stm|work=BBC News|title=Scots Labour MPs rebel on Trident|date=14 March 2007|access-date=1 March 2016|archive-date=25 March 2007|archive-url=https://web.archive.org/web/20070325011405/http://news.bbc.co.uk/1/hi/scotland/6452275.stm|url-status=live}}</ref>

[[Faslane Peace Camp]] is permanently sited near Faslane naval base. It has been occupied continuously, albeit in different locations, since 12 June 1982.<ref>{{cite web |url=https://faslanepeacecamp.wordpress.com/35th-anniversary-2017/ |title=35th Anniversary (2017) |publisher=Faslane Peace Camp |access-date=28 March 2016 |archive-date=28 March 2018 |archive-url=https://web.archive.org/web/20180328103217/https://faslanepeacecamp.wordpress.com/35th-anniversary-2017/ |url-status=live }}</ref> In 2006, a year-long protest at Trident's base at Faslane aimed to blockade the base every day for a year. More than 1,100 people were arrested.<ref>{{cite news |newspaper=The Guardian |first=Severin |last=Carrell |title=170 held at last Faslane demo |url=https://www.theguardian.com/uk/2007/oct/02/nuclear.scotland |date=3 October 2007 |access-date=28 March 2016 |archive-date=5 October 2014 |archive-url=https://web.archive.org/web/20141005233926/http://www.theguardian.com/uk/2007/oct/02/nuclear.scotland |url-status=live }}</ref>

During the 2020 coronavirus pandemic a letter was circulated to MPs by the Bertrand Russell Peace Foundation which stated, “It is completely unacceptable that the UK continues to spend billions of pounds on deploying and modernising the Trident Nuclear Weapon System when faced with the threats to health, climate change and world economies that Coronavirus poses.” Signatories included Commander Robert Forsyth RN (Ret'd), a former nuclear submariner; Commander Robert Green RN (Ret'd), a former nuclear-armed aircraft bombardier-navigator and Staff Officer (Intelligence) to CINFLEET in the Falklands War; and Commander Colin Tabeart RN (Ret'd), a former Senior Engineer Officer on a Polaris submarine.<ref>{{cite news|newspaper=Plymouth Live|url=https://www.plymouthherald.co.uk/news/uk-world-news/ex-royal-navy-commanders-question-4011611|title=Ex Royal Navy Commanders question Trident need as coronavirus costs rise|date=2 April 2020|access-date=3 May 2020|archive-date=29 January 2021|archive-url=https://web.archive.org/web/20210129081910/https://www.plymouthherald.co.uk/news/uk-world-news/ex-royal-navy-commanders-question-4011611?utm_source=facebook.com&utm_medium=social&utm_campaign=sharebar&fbclid=IwAR0aU61X5npRiFjSN81P46bycTtjqPBagWPu-cK2CbHhuialceAWvYuq1nE|url-status=live}}</ref> Following this the MoD updated its online instruction notice to staff on public communications to say, “All contact with the media or communication in public by members of the armed forces and MoD civilians where this relates to defence or government business must be authorised in advance”.<ref>{{cite news|newspaper=The National|title=MoD 'gagging' its staff from speaking publicly about Trident|date=3 May 2020|url=https://www.thenational.scot/news/18422680.mod-gagging-staff-speaking-publicly-trident/|access-date=3 May 2020|archive-date=4 May 2020|archive-url=https://web.archive.org/web/20200504024221/https://www.thenational.scot/news/18422680.mod-gagging-staff-speaking-publicly-trident/|url-status=live}}</ref>

==Reviews==
[[File:Officer of the watch aboard HMS Vanguard. MOD 45159466.jpg|thumb|upright|Officer of the watch aboard {{HMS|Vanguard|S28|6}}]]

===Royal United Services Institute===

The [[Royal United Services Institute]] (RUSI), a British defence and security [[think tank]], released a paper in July 2010 assessing four possible options for maintaining both an effective nuclear deterrent and also reducing costs in light of anticipated budget restrictions.{{sfn|Chalmers|2010|p=1}} These proposals were motivated by the fact that funding for the Trident renewal programme now had to come from the core Ministry of Defence budget.<ref>{{cite news|url=https://www.bbc.co.uk/news/uk-10812825|title=Trident costs must come from MoD budget, Osborne says|date=30 July 2010|work=BBC News|access-date=10 September 2010|archive-date=9 September 2010|archive-url=https://web.archive.org/web/20100909062807/http://www.bbc.co.uk/news/uk-10812825|url-status=live}}</ref> Four alternatives were considered: Trident submarines on continuous patrol; Trident submarines not on patrol continuously; attack submarines armed with nuclear cruise missiles; and land-based nuclear weapons.{{sfn|Chalmers|2010|p=1}} The paper concluded that "given the opportunity costs for conventional capabilities that current plans for Trident renewal are due to incur over the next decade...there is now a growing case for a re-examination of whether there are less expensive means of pursuing this objective. A key element of such a review is likely to be a reconsideration of the need to maintain a commitment to CASD in strategic circumstances that are now very different from those in which it was first introduced."{{sfn|Chalmers|2010|p=5}}

===Trident Alternatives Review===
The 2013 Trident Alternatives Review was an 18-month study led by the Cabinet Office that was aimed at establishing whether or not there were credible alternatives to the UK's submarine-based CASD. Accordingly, the review analysed a range of delivery systems and warhead designs with respect to their affordability and effectiveness against potential targets.<ref name="Trident Alternatives Review">{{cite web |title=Trident Alternatives Review |url=https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/212745/20130716_Trident_Alternatives_Study.pdf |publisher=British government |access-date=8 July 2014 |archive-date=11 August 2014 |archive-url=https://web.archive.org/web/20140811135748/https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/212745/20130716_Trident_Alternatives_Study.pdf |url-status=live }}</ref> Ultimately, the Trident Alternatives Review came to the conclusion that there were alternatives to Trident that "would enable the UK to be capable of inflicting significant damage such that most potential adversaries around the world would be deterred", but none would "offer the same degree of resilience as the current posture".  The review asserted that whether or not cruise missile-based systems offer a credible alternative was contingent upon a political judgement on whether the UK could accept a "significant increase in vulnerability" and a reduction in who it could deter.<ref name="Trident Alternatives Review"/>

The publication of the report was met with a mixed reception from different political parties and non-governmental organisations (NGOs) in the field of non-proliferation and disarmament. While it was welcomed by the prime minister, [[David Cameron]], as having confirmed the necessity of like-for-like replacement of Trident, Liberal Democrat cabinet minister [[Danny Alexander]] deemed it a demonstration of the fact there are "credible and viable alternatives to the UK's current approach to nuclear deterrence." NGOs including the [[British American Security Information Council]] (BASIC), a non-proliferation and disarmament think-tank, criticised the report for its limited scope and its failure to engage with a wider array of considerations related to nuclear weapons, including environmental and humanitarian issues.<ref>{{cite news|title=UK has alternatives to Trident—Danny Alexander|url=https://www.bbc.co.uk/news/uk-politics-23117303|publisher=BBC|access-date=8 July 2014|archive-date=23 October 2013|archive-url=https://web.archive.org/web/20131023152940/http://www.bbc.co.uk/news/uk-politics-23117303|url-status=live}}</ref><ref>{{cite web|last1=Ingram|first1=Paul|title=Reading the findings of the UK Trident Alternatives Review|url=http://www.basicint.org/sites/default/files/basictar-prebrief_0.pdf|publisher=British American Security Information Council|access-date=8 July 2014|archive-date=14 July 2014|archive-url=https://web.archive.org/web/20140714130613/http://www.basicint.org/sites/default/files/basictar-prebrief_0.pdf|url-status=live}}</ref>

===The Trident Commission===
In 2011, BASIC launched an independent cross-party Commission to initiate a deeper national debate on the UK's nuclear weapons policy and examine questions around the contentious issue of Trident renewal. The Commission operated under the chairmanship of former Labour Secretary of State for Defence, [[Des Browne|Lord Browne of Ladyton]]; former Conservative Defence and Foreign Secretary, Sir Malcolm Rifkind; and Sir [[Menzies Campbell]], former leader of the Liberal Democrats and Shadow Foreign Secretary.<ref>{{cite web|title=Trident Commission|date=5 January 2011 |url=http://www.basicint.org/tridentcommission/|publisher=British American Security Information Council|access-date=8 July 2014|archive-date=8 July 2014|archive-url=https://web.archive.org/web/20140708043358/http://www.basicint.org/tridentcommission/|url-status=live}}</ref> After three years' of deliberation, the Commission released its final report on 1 July 2014. It suggested, with important caveats, that the UK should retain a nuclear deterrent. The conclusion acknowledged that "it remains crucial that the UK show keen regard for its position within the international community and for the shared responsibility to achieve progress in global nuclear disarmament."<ref>{{cite web|title=The Trident Commission: Concluding Report|url=http://www.basicint.org/sites/default/files/trident_commission_finalreport.pdf|publisher=British American Information Council|access-date=8 July 2014|archive-date=14 July 2014|archive-url=https://web.archive.org/web/20140714131305/http://www.basicint.org/sites/default/files/trident_commission_finalreport.pdf|url-status=live}}</ref>

BASIC's interpretation of the report also focused on this point, emphasising that the commissioners "agreed that the health of the global strategic environment, particularly nuclear non-proliferation, is critical to national security and is a central consideration. They talk of the need for Britain to maintain its 'glide path down towards disarmament', to ensure that the renewal decisions the next government will be taking have consistency with the trajectory set by successive recent governments, and that the UK should continue to be 'at the forefront of the multilateral disarmament process.'"<ref>{{cite web|title=A BASIC Guide to Interpreting the Trident Commission's Concluding Report|url=http://www.basicint.org/sites/default/files/basic_guide_to_tccr.pdf|publisher=British American Security Information Council|access-date=8 July 2014|archive-date=14 July 2014|archive-url=https://web.archive.org/web/20140714153042/http://www.basicint.org/sites/default/files/basic_guide_to_tccr.pdf|url-status=live}}</ref>

==Renewal==
[[File:Jeremy Corbyn Says -StopTrident - 2.jpg|thumb|right|Former [[Leader of the Opposition (United Kingdom)|Leader of the Opposition]], [[Jeremy Corbyn]] speaks at the #StopTrident rally at [[Trafalgar Square]] on 27 February 2016]]

===2006 Defence White Paper===
The ''Vanguard''-class submarines were built with a 25-year life expectancy, taking them into the 2020s. Trident II D-5 missiles are expected to continue in service until at least 2040 following an upgrade.<ref name="successor">{{cite web|url=https://www.gov.uk/government/publications/successor-submarine-programme-factsheet/successor-submarine-programme-factsheet|title=Successor submarine programme: factsheet|publisher=MoD|access-date=1 March 2016|archive-date=13 July 2018|archive-url=https://web.archive.org/web/20180713042054/https://www.gov.uk/government/publications/successor-submarine-programme-factsheet/successor-submarine-programme-factsheet|url-status=live}}</ref> A December 2006 Ministry of Defence [[white paper]], entitled "The Future of the United Kingdom's Nuclear Deterrent", recommended that the nuclear weapons should be maintained and outlined measures that would do so until the 2040s. It advocated the currently preferred submarine-based system, as it remained the cheapest and most secure deterrence option available. Costs for this option are estimated at £15–20&nbsp;billion based on:
* £0.25 billion to participate in US Trident D-5 missile life extension programme.
* £11–14 billion for a class of four new SSBNs.
* £2–3 billion for refurbishing warheads.
* £2–3 billion for infrastructure.<ref name="WhitePaper">{{cite web|url=http://www.mod.uk/NR/rdonlyres/AC00DD79-76D6-4FE3-91A1-6A56B03C092F/0/DefenceWhitePaper2006_Cm6994.pdf|title=The Future of the United Kingdom's Nuclear Deterrent|date=4 December 2006|publisher=[[Ministry of Defence (United Kingdom)|Ministry of Defence]]|access-date=5 December 2006|archive-date=6 December 2006|archive-url=https://web.archive.org/web/20061206004317/http://www.mod.uk/NR/rdonlyres/AC00DD79-76D6-4FE3-91A1-6A56B03C092F/0/DefenceWhitePaper2006_Cm6994.pdf|url-status=live}}</ref>

These 2006/07 prices would equate to about £25bn for the Successor-class submarines as they were provisionally named; the 2011 Initial Gate report confirmed estimates of £2-3bn each for the warheads and infrastructure.<ref name=SIG /> These cost estimates exclude the ''Vanguard'' five-year life extension and decommissioning, and it is unclear if new Trident missiles will need to be purchased for the life extension programme.<ref name=CommonsWhitePaperReport>{{cite web|url=https://publications.parliament.uk/pa/cm200607/cmselect/cmdfence/225/225i.pdf|title=The Future of the UK's Strategic Nuclear Deterrent: the White Paper|date=7 March 2007|publisher=[[British House of Commons|House of Commons]] [[Defence Select Committee|Defence Committee]]|access-date=15 March 2007|archive-date=20 June 2009|archive-url=https://web.archive.org/web/20090620205524/http://www.publications.parliament.uk/pa/cm200607/cmselect/cmdfence/225/225i.pdf|url-status=live}}</ref> Running costs would be about £1.5&nbsp;billion per year at 2006 prices.<ref name=CommonsWhitePaperReport/> The paper suggested parts of the existing Trident system be refitted to some extent to prolong their lives. However, the relatively short (five years) life extension potential of the ''Vanguard'' class meant that a new class of SSBNs should replace it in the 2020s. The first boat of the new SSBN class would take 17 years to be designed and built, making a five-year life extension of the ''Vanguard'' class necessary.<ref name="WhitePaper"/>

===Parliamentary support===

A decision on the renewal of Trident was made on 4 December 2006. 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 £20bn 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% 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.<ref>{{cite news |url=http://news.bbc.co.uk/2/hi/uk_news/politics/6205174.stm |title=UK nuclear weapons plan unveiled |publisher=BBC |date=4 December 2006 |access-date=29 July 2018 |archive-date=8 November 2012 |archive-url=https://web.archive.org/web/20121108031010/http://news.bbc.co.uk/2/hi/uk_news/politics/6205174.stm |url-status=live }}</ref>

On 14 March 2007, the Labour government won House of Commons support for the plans to renew the submarine system. The proposals were passed by a majority of 248.<ref name="bbcvote">{{cite news|url=http://news.bbc.co.uk/2/hi/uk_news/politics/6448173.stm|title=Trident plan wins Commons support|date=15 March 2007|work=BBC News|access-date=15 March 2007|archive-date=29 January 2021|archive-url=https://web.archive.org/web/20210129050732/http://news.bbc.co.uk/2/hi/uk_news/politics/6448173.stm|url-status=live}}</ref><ref name="replacement">{{cite news|url=http://news.bbc.co.uk/1/hi/uk_politics/6448173.stm|title=Trident plan wins Commons support|date=14 March 2007|work=BBC News|access-date=14 March 2007|archive-date=16 March 2007|archive-url=https://web.archive.org/web/20070316101938/http://news.bbc.co.uk/1/hi/uk_politics/6448173.stm|url-status=live}}</ref> Despite a clarification that the vote was just for the concept stage of the new system, 95 Labour MPs rebelled, and it was only passed with the support of the opposition Conservative Party.<ref name="bbcvote"/><ref name="abcnews">{{cite news|url=http://www.abc.net.au/news/newsitems/200703/s1872177.htm|title=Blair wins Trident nuclear arsenal vote|date=15 March 2007|publisher=[[ABC News (Australia)|ABC News]]|access-date=15 March 2007|url-status=dead |archive-url=https://web.archive.org/web/20070317031342/http://www.abc.net.au/news/newsitems/200703/s1872177.htm|archive-date=17 March 2007}}</ref> It was the first time MPs had been given the chance to vote on whether the UK should remain a [[Nuclear weapons and the United Kingdom|nuclear power]], and the biggest rebellion since the beginning of the 2003 [[Iraq War]].<ref name="bbcvote"/>
The Labour government proposed that the final decision to manufacture should be made in 2014.<ref name=pugwash-201107/> The new [[2010 United Kingdom government formation|2010 coalition government]] agreed "that the renewal of Trident should be scrutinised to ensure value for money." Research and development work continued with an Initial Gate procurement decision, but the Main Gate decision to manufacture a replacement was rescheduled for 2016, after the [[2015 United Kingdom general election|2015 general election]].{{refn|group=note|The business case presented at Initial Gate includes the programme plan and costing for the procurement. The Main Gate business case is a key deliverable from the assessment stage. The process and products are similar to those used at Initial Gate but with a higher degree of maturity expected at this stage to inform the decision on whether or not to proceed with procurement.<ref>{{cite web |url=http://www.modaf.com/files/MODAF%20Acquisition%20Deskbook%20v0.9.pdf |title=MOD Architectural Framework Acquisition Community of Interest Deskbook |publisher=Ministry of Defence |date=29 July 2005 |access-date=8 May 2018 |archive-date=26 March 2016 |archive-url=https://web.archive.org/web/20160326094104/http://www.modaf.com/files/MODAF%20Acquisition%20Deskbook%20v0.9.pdf |url-status=live }}</ref>}}<ref name=pugwash-201107>{{cite web |url=http://www.basicint.org/sites/default/files/briefing_3_-_initial_gate.pdf |title=Trident: The Initial Gate Decision |series=Briefings on Nuclear Security |publisher=BASIC |date=July 2011 |access-date=18 July 2018 |archive-date=3 August 2016 |archive-url=https://web.archive.org/web/20160803111531/http://www.basicint.org/sites/default/files/briefing_3_-_initial_gate.pdf |url-status=live }}</ref> The vote on whether to order the Successor-class was held on 18 July 2016 in the House of Commons; the motion passed with a significant majority,<ref>{{cite web|url=https://www.bbc.co.uk/news/uk-politics-36830923|title=MPs approve Trident renewal|date=18 July 2016|work=BBC News|access-date=18 July 2016|archive-date=24 March 2018|archive-url=https://web.archive.org/web/20180324190112/http://www.bbc.co.uk/news/uk-politics-36830923|url-status=live}}</ref> extending the programme's life until at least the 2060s. Although 48 Labour MPs voted against it, 41 did not vote, and 140 Labour votes were cast in favour of the motion.<ref>{{cite web |url=https://www.bbc.com/news/uk-politics-36830923 |title=MPs vote to renew Trident weapons system |last=Kuenssberg |first=Laura |date=19 July 2016 |publisher=BBC |access-date=19 July 2016 |quote=Jeremy Corbyn has been heckled and accused of lying by his own MPs and told he was "defending the countries’ enemies" as he announced he would vote against renewing Trident. |archive-date=18 July 2016 |archive-url=https://web.archive.org/web/20160718213716/http://www.bbc.com/news/uk-politics-36830923 |url-status=live }}</ref>

[[File:StopTrident rally at Trafalgar Square.jpg|thumb|left|upright=1.2|[[Leanne Wood]] speaks at the #StopTrident rally on 27 February 2016. She was arrested on 8 January 2007 for protesting against the UK's Trident nuclear missile programme at Faslane.<ref>{{cite news |author=Auslan Cramb |url=https://www.telegraph.co.uk/news/uknews/1538937/Nine-are-held-in-Faslane-demo.html |title=Nine are held in Faslane demo |newspaper=[[The Daily Telegraph]] |location=London |date=9 January 2007 |access-date=7 June 2011 |archive-date=4 June 2011 |archive-url=https://web.archive.org/web/20110604052620/http://www.telegraph.co.uk/news/uknews/1538937/Nine-are-held-in-Faslane-demo.html |url-status=live }}</ref>]]

===2010 Strategic Defence and Security Review===
The 2010 Strategic Defence and Security Review concluded that the Successor-class submarines would have eight operational missiles carrying no more than 40 operational warheads between them. This would allow the UK to reduce its stocks of operational warheads from 160 to 120, and the overall stockpile from no more than 225 to no more than 180.<ref name=SIG /> They would be carried in a 12-missile [[Columbia-class submarine#Common missile compartment|Common Missile Compartment]] designed in collaboration with the US which could accommodate the current Trident II D-5 missiles and any replacement missile once the D-5 reaches the end of its expected life in the 2040s.<ref name=SIG>{{cite web | url= http://www.mod.uk/NR/rdonlyres/7F9F5815-C67B-47B1-B5C4-168E8AB50DC3/0/submarine_initial_gate.pdf | title= The United Kingdom's Future Nuclear Deterrent: The Submarine Initial Gate Parliamentary Report | publisher= UK Ministry of Defence | date= May 2011 | access-date= 18 July 2018 | archive-date= 14 September 2012 | archive-url= https://web.archive.org/web/20120914100728/http://www.mod.uk/NR/rdonlyres/7F9F5815-C67B-47B1-B5C4-168E8AB50DC3/0/submarine_initial_gate.pdf | url-status= live }}</ref>

===Expert opinion===
Two non-representative polls of experts from the RUSI and the Royal Institute of International Affairs (commonly known as [[Chatham House]]) were conducted in 2010. The RUSI found a majority for those who think the benefits of Trident outweigh the costs (53%) compared to those that think the costs outweigh the benefits (13%) or are evenly balanced (34%). The Chatham House poll found a minority in favour of Trident replacement (22%), with more in favour of replacing with a cheaper system (43%) and 29% saying the UK should not replace Trident at all.<ref>{{cite web |url=http://www.basicint.org/sites/default/files/tridentpoliticspublicopinion_basicjul2013.pdf |title=Trident in UK Politics and Public Opinion |page=23 |access-date=18 July 2018 |archive-date=2 December 2016 |archive-url=https://web.archive.org/web/20161202080846/http://www.basicint.org/sites/default/files/tridentpoliticspublicopinion_basicjul2013.pdf |url-status=dead }}</ref>

===Public opinion===
In April 2015, a [[YouGov]] poll found that 38% of people thought that Trident should be replaced in full, 28% wanted to replace it with a cheaper system, 19% thought the UK should completely give up its nuclear weapons, and 15% did not know.<ref>{{cite web |url=https://d25d2506sfb94s.cloudfront.net/cumulus_uploads/document/oqslggwc4a/YG-Archive-Pol-Sunday-Times-results-110415.pdf |title=YouGov Poll p.13 |access-date=27 November 2016 |archive-date=28 October 2015 |archive-url=https://web.archive.org/web/20151028184059/https://d25d2506sfb94s.cloudfront.net/cumulus_uploads/document/oqslggwc4a/YG-Archive-Pol-Sunday-Times-results-110415.pdf |url-status=live }}</ref> In September 2015, a [[Survation]] poll found that 29% agreed that Trident should be reformed to make it cheaper, 26% that it should be renewed in full, and 18% that it should be scrapped. 27% did not know.<ref>{{cite news |newspaper=HuffPost |url=http://www.huffingtonpost.co.uk/2015/09/25/jeremy-corbyn-poll-trident-security-labour-conference_n_8195562.html |access-date=24 March 2018 |first=Graeme |last=Demianyk |date=25 September 2015 |title=Labour Party Conference HuffPost Poll: Less Than One In Five Voters Back Scrapping Trident |archive-date=12 June 2018 |archive-url=https://web.archive.org/web/20180612162258/https://www.huffingtonpost.co.uk/2015/09/25/jeremy-corbyn-poll-trident-security-labour-conference_n_8195562.html |url-status=live }}</ref> Nuclear weapons are not the nation's biggest issue, with just 2% of people saying that it was the nation's biggest worry in May 2015, compared to 21% in June 1987.<ref>{{cite web|url=http://blogs.channel4.com/factcheck/factcheck-britain-scrap-trident/21868|title=FactCheck: Does Britain want to scrap Trident?|url-status=dead|archive-url=https://web.archive.org/web/20151106151833/http://blogs.channel4.com/factcheck/factcheck-britain-scrap-trident/21868|archive-date=6 November 2015}}</ref>

===''Dreadnought''-class submarine===
{{main|Dreadnought-class submarine}}
In February 2016, [[BAE Systems]] began design work on prototypes of the new submarines.<ref>{{cite news|url=https://www.telegraph.co.uk/finance/newsbysector/industry/defence/12146831/BAE-gets-201m-for-fresh-design-work-on-new-nuclear-submarines.html|title=BAE gets £201m for fresh design work on new nuclear submarines|newspaper=The Telegraph|date=8 February 2016|access-date=1 March 2016|archive-date=15 March 2016|archive-url=https://web.archive.org/web/20160315145708/http://www.telegraph.co.uk/finance/newsbysector/industry/defence/12146831/BAE-gets-201m-for-fresh-design-work-on-new-nuclear-submarines.html|url-status=live}}</ref> The Successor class was officially named the {{sclass|Dreadnought|submarine|4}} on 21 October 2016.<ref>{{cite press release|url=https://www.gov.uk/government/news/new-successor-submarines-named|title=New Successor Submarines Named|publisher=Government of the United Kingdom|date=21 October 2016|access-date=21 October 2016|archive-date=22 October 2016|archive-url=https://web.archive.org/web/20161022023028/https://www.gov.uk/government/news/new-successor-submarines-named|url-status=live}}</ref><ref name="successor"/> The submarines were expected to become operational starting in 2028, with the current fleet phased out by 2032.<ref>{{cite news |url=http://www.itv.com/news/2016-07-18/everything-you-need-to-know-about-trident-britains-nuclear-deterrent/ |title=Everything you need to know about Trident – Britain's nuclear deterrent |date=18 July 2016 |publisher=ITV News |access-date=20 July 2016 |quote=The £40&nbsp;billion construction of a new fleet, Successor, could begin this year and be operational by 2028 while the current fleet will be phased out by 2032. |archive-date=20 July 2016 |archive-url=https://web.archive.org/web/20160720011450/http://www.itv.com/news/2016-07-18/everything-you-need-to-know-about-trident-britains-nuclear-deterrent/ |url-status=live }}</ref><ref>{{cite news|url=https://www.bbc.co.uk/news/uk-politics-36830923|title=MPs approve Trident renewal|date=18 July 2016|work=BBC News|access-date=18 July 2016|archive-date=24 March 2018|archive-url=https://web.archive.org/web/20180324190112/http://www.bbc.co.uk/news/uk-politics-36830923|url-status=live}}</ref>

In October 2015, [[Reuters]] estimated it would cost £167&nbsp;billion over its 30-year lifespan, or £5.56&nbsp;billion per year; this figure was disputed by Michael Fallon.<ref>{{cite news|url=http://uk.reuters.com/article/uk-britain-defence-trident-idUKKCN0SZ2IC20151110|title=Britain denies report nuclear deterrent to cost 167&nbsp;billion pounds|date=10 November 2015|access-date=1 March 2016|work=Reuters|archive-date=21 July 2016|archive-url=https://web.archive.org/web/20160721152622/http://uk.reuters.com/article/uk-britain-defence-trident-idUKKCN0SZ2IC20151110|url-status=dead}}</ref> The Ministry of Defence put the cost of building, testing and commissioning the replacement vessels at £31&nbsp;billion (plus a contingency fund of £10&nbsp;billion) over 35 years. This amounts to 0.2 per cent of government spending, or 6 per cent of defence spending.<ref name="modfeb16"/> [[Crispin Blunt]], Chair of the Foreign Affairs Select Committee, estimated in July 2016 that the programme would cost £179&nbsp;billion in total over its lifetime.<ref>{{cite web |url=https://ukdefencejournal.org.uk/british-parliament-votes-renew-trident-nuclear-weapons/ |title=British parliament votes to renew Trident |last1=Allison |first1=George |date=18 July 2016 |publisher=UK Defence Journal |access-date=20 July 2016 |quote=The Successor class is the proposed replacement for the Vanguard class ballistic missile submarines. They will carry Trident D-5 missiles, the vehicle for delivering the UK's nuclear weapons. |archive-date=9 August 2016 |archive-url=https://web.archive.org/web/20160809020646/https://ukdefencejournal.org.uk/british-parliament-votes-renew-trident-nuclear-weapons/ |url-status=live }}</ref>

For the 2018/19 financial year the National Audit Office found that spending on the nuclear deterrent will cost £5.2&nbsp;billion, or 14% of the defence budget, with £600&nbsp;million of contingency funding used. Costs were projected at about £51&nbsp;billion over the following 10 years, £2.9&nbsp;billion above the projected budget which already anticipated finding £3&nbsp;billion of savings, which the ''Daily Telegraph'' described as a £6&nbsp;billion shortfall.<ref name=guardian-20180522>{{cite news |url=https://www.theguardian.com/uk-news/2018/may/22/mod-faces-29bn-nuclear-funding-gap-say-auditors |title=MoD faces £2.9bn nuclear funding gap, say auditors |last=Syal |first=Rajeev |newspaper=The Guardian |date=22 May 2018 |access-date=22 May 2018 |archive-date=22 May 2018 |archive-url=https://web.archive.org/web/20180522034717/https://www.theguardian.com/uk-news/2018/may/22/mod-faces-29bn-nuclear-funding-gap-say-auditors |url-status=live }}</ref><ref name=telegraph-20180522>{{cite news |url=https://www.telegraph.co.uk/business/2018/05/21/spending-watchdog-warns-6bn-risk-britains-nuclear-submarine/ |title=Royal Navy's nuclear submarines face £6bn black hole |last=Tovey |first=Alan |newspaper=The Daily Telegraph |date=22 May 2018 |access-date=22 May 2018 |archive-date=21 May 2018 |archive-url=https://web.archive.org/web/20180521231516/https://www.telegraph.co.uk/business/2018/05/21/spending-watchdog-warns-6bn-risk-britains-nuclear-submarine/ |url-status=live }}</ref>

== See also ==

* [[Armed forces in Scotland]]
* [[Military history of Scotland]]

==Footnotes==
{{reflist|group=note}}

==Notes==
{{reflist}}

==References==
{{refbegin|30em}}
* {{cite journal |last=Baylis |first=John |date=June 2008 |title=The 1958 Anglo-American Mutual Defence Agreement: The Search for Nuclear Interdependence |journal=The Journal of Strategic Studies |issn=0140-2390 |volume=31 |issue=3 |pages=425–466 |doi=10.1080/01402390802024726|s2cid=153628935 }}
* {{cite book |last1=Bowie |first1=Christopher J. |first2=Alan |last2=Platt |title=British Nuclear Policymaking |publisher=Rand Corporation |location=Santa Monica, California |date=1984 |url=https://www.rand.org/pubs/reports/R3085.html |access-date=10 July 2018 |isbn=0-8330-0534-0 |oclc=29212035 |archive-date=15 July 2018 |archive-url=https://web.archive.org/web/20180715160027/https://www.rand.org/pubs/reports/R3085.html |url-status=live }}
* {{cite journal |last=Brown |first=N. |title=Britain's Strategic Weapons I. Manned Bombers |journal=The World Today |volume=20 |issue=7 |pages=293–298 |jstor=40393629 |date=July 1964 }}
* {{cite book |last1=Butler |first1=Nicola |first2=Mark |last2=Bromley |title=Secrecy and Dependence: The UK Trident System in the 21st Century |id=BASIC Research Report, Number 2001.3 |date=November 2001 |publisher=British American Information Council |url=http://www.basicint.org/sites/default/files/PUB010301.pdf |access-date=13 July 2018 |isbn=978-1-874533-44-3 |oclc=78965689 |archive-date=13 July 2018 |archive-url=https://web.archive.org/web/20180713010503/http://www.basicint.org/sites/default/files/PUB010301.pdf |url-status=dead }}
* {{cite journal |last=Chalmers |first=Malcolm |title=Bombs Away? Britain and Nuclear Weapons under New Labour |journal=Security Dialogue |issn=0967-0106 |volume=30 |issue=1 |pages=61–74 |date=1 March 1999 |doi=10.1177/0967010699030001005 |s2cid=143332405 }}
* {{cite book |last=Chalmers |first=Malcolm |title=Continuous At-Sea Deterrence: Costs and Alternatives |url=http://www.rusi.org/downloads/assets/CASD.pdf |publisher=[[RUSI]] |date=July 2010 |access-date=10 September 2010 |url-status=dead |archive-url=https://web.archive.org/web/20101231014329/http://www.rusi.org/downloads/assets/CASD.pdf |archive-date=31 December 2010 }}
* {{cite journal |last=Dombey |first=Norman |title=What is Trident for? |date=April 2007 |url=http://www.lrb.co.uk/v29/n07/norman-dombey/what-is-trident-for |access-date=23 March 2018 |journal=London Review of Books |issn=0260-9592 |volume=29 |issue=7 |pages=33–34 |archive-date=27 September 2018 |archive-url=https://web.archive.org/web/20180927123845/https://www.lrb.co.uk/v29/n07/norman-dombey/what-is-trident-for |url-status=live }}
* {{cite journal |last=Doyle |first=Suzanne |year=2017a |title=The United States Sale of Trident to Britain, 1977–1982: Deal Making in the Anglo–American Nuclear Relationship |journal=Diplomacy & Statecraft |issn=0959-2296 |volume=28 |issue=3 |pages=477–493 |doi=10.1080/09592296.2017.1347447 |s2cid=158987476 |url=https://ueaeprints.uea.ac.uk/63886/1/Accepted_manuscript.pdf |access-date=9 July 2019 |archive-date=30 April 2019 |archive-url=https://web.archive.org/web/20190430132120/https://ueaeprints.uea.ac.uk/63886/1/Accepted_manuscript.pdf |url-status=live }}
* {{cite journal |last=Doyle |first=Suzanne |year=2017b |title=A Foregone Conclusion? The United States, Britain and the Trident D5 Agreement |journal=Journal of Strategic Studies |issn=0140-2390 |volume=40 |issue=6 |pages=867–894 |doi=10.1080/01402390.2016.1220366 |s2cid=157200631 |url=https://ueaeprints.uea.ac.uk/59912/1/S.DoyleTridentD5Submission.pdf |access-date=9 July 2019 |archive-date=21 July 2018 |archive-url=https://web.archive.org/web/20180721081014/https://ueaeprints.uea.ac.uk/59912/1/S.DoyleTridentD5Submission.pdf |url-status=live }}
* {{cite journal |last=Doyle |first=Suzanne |year=2018 |title=Preserving the Global Nuclear Order: The Trident Agreements and the Arms Control Debate, 1977–1982 |journal=The International History Review |volume=40 |issue=5 |pages=1174–1190 |issn=1949-6540 |doi=10.1080/07075332.2018.1430047 |s2cid=158388064 |url=https://ueaeprints.uea.ac.uk/id/eprint/66183/1/Accepted_manuscript.pdf |access-date=11 September 2020 |archive-date=29 January 2021 |archive-url=https://web.archive.org/web/20210129102045/https://ueaeprints.uea.ac.uk/id/eprint/66183/1/Accepted_manuscript.pdf |url-status=live }}
* {{cite book |last=Gowing |first=Margaret |author-link=Margaret Gowing |title=Britain and Atomic Energy 1939–1945  |publisher=Macmillan |year=1964 |location=London |oclc=3195209 }}
* {{cite book |last1 = Gowing |first1 = Margaret   |first2 = Lorna |last2 = Arnold |author-link2=Lorna Arnold |year = 1974 |title=Independence and Deterrence: Britain and Atomic Energy, 1945–1952, Volume 1, Policy Making |publisher= Macmillan|location = London |isbn = 0-333-15781-8 |oclc = 611555258 }}
* {{cite book |last=Grove |first=Eric J. |author-link=Eric Grove |title=Vanguard to Trident; British Naval Policy since World War II |location=Annapolis, Maryland |publisher=United States Naval Institute |year=1987 |isbn=0-87021-552-3 |oclc=15081825 }}
* {{cite book |last=Jones |first=Jeffrey |series=The Official History of the UK Strategic Nuclear Deterrent |title=Volume I: From the V-Bomber Era to the Arrival of Polaris, 1945–1964 |location=Milton Park, Abingdon, Oxfordshire |publisher=Routledge |year=2017 |isbn=978-1-138-67493-6 |oclc=1005663721 }}
* {{cite book |last=Larkin |first=Bruce D. |year=1989 |title=Nuclear Designs: Great Britain, France and China in the Global Governance of Nuclear Arms |location=New Brunswick, New Jersey |publisher=Transaction Publishers |isbn=978-1-4128-2983-0 |oclc=933970833 }}
* {{cite book |last=Moore |first=Richard |year=2010 |title=Nuclear Illusion, Nuclear Reality: Britain, the United States and Nuclear Weapons 1958–64 |publisher=Palgrave MacMillan |series=Nuclear Weapons and International Security since 1945 |location=Basingstoke, Hampshire  |isbn=978-0-230-21775-1 |oclc=705646392 }}
* {{cite book |last=Mosher |first=David |year=1993 |title=Rethinking the Trident Force |location=Washington, DC |publisher=Congressional Budget Office |oclc=713559648 }}
* {{cite book |last=Nailor |first=Peter |title=The Nassau Connection: The Organisation and Management of the British Polaris Project |publisher=HMSO |year=1988 |isbn=0-11-772526-9 |oclc=231046793 }}
* {{cite book |author=National Audit Office |title=Ministry of Defence and Property Services Agency: Control and Management of the Trident Programme |author-link=National Audit Office (United Kingdom) |location=London |publisher=Her Majesty's Stationery Office |date=29 June 1987 |isbn=0-10-202788-9 |oclc=655304084 }}
* {{cite book |last=Navias |first=Martin S. |title=British Weapons and Strategic Planning, 1955–1958 |location=Oxford |publisher=Oxford University Press |year=1991 |isbn=978-0-19-827754-5|oclc=22506593 }}
* {{cite journal |last=Priest |first=Andrew |title=In American Hands: Britain, the United States and the Polaris Nuclear Project 1962–1968  |journal=Contemporary British History |issn=1361-9462 |date=September 2005 |volume=19 |issue=3 |pages=353–376 | doi=10.1080/13619460500100450 |s2cid=144941756 }}
* {{cite report |last=Ritchie |first=Nick |title=Trident and British Identity: Letting Go of Nuclear Weapons |publisher=University of Bradford |year=2008 |location=Bradford, West Yorkshire |url=https://bradscholars.brad.ac.uk/handle/10454/917 |access-date=14 July 2018 |oclc=682883281 |hdl=10454/917 }}
* {{cite book |last=Ritchie |first=Nick |title=Nuclear Weapons-Free World?: Britain, Trident and the Challenges Ahead |publisher=Palgrave Macmillan |year=2014 |location=Basingstoke, Hampshire |isbn=978-1-349-33185-7 |oclc=951512317 }}
* {{cite journal |last=Ritchie |first=Nick |year=2016 |title=Nuclear identities and Scottish independence |journal=The Nonproliferation Review |issn= 1073-6700  |volume=23 |issue=5–6 |pages=653–675 |doi=10.1080/10736700.2017.1345517 |doi-access=free |url=https://eprints.whiterose.ac.uk/120167/1/2016_July_NP_Review_Scotland_NW_article7.docx }}
* {{cite book |editor-last=Saunders |editor-first=Stephen |year=2004 |title=Jane's Fighting Ships, 2004–2005 |location=London |publisher=Jane's Information Group Limited |isbn=0-7106-2623-1 |oclc=973573307 }}
* {{cite journal |last=Scott |first=Len |title=Selling or Selling Out Nuclear Disarmament? Labour, the Bomb, and the 1987 General Election |journal=The International History Review |issn=0707-5332 |date= March 2012 |volume=34 |issue=1 |pages=115–137 |doi=10.1080/07075332.2012.620242 |s2cid=154319694 }}
* {{cite book |last=Spinardi |first=Graham |title=From Polaris to Trident: The Development of Fleet Ballistic Technology |location=Cambridge |publisher=Cambridge University Press  |year=1994 |isbn=0-521-41357-5 |oclc=27339433 }}
* {{cite book |last=Stoddart |first=Kristan |title=Facing Down the Soviet Union: Britain, the USA, NATO and Nuclear Weapons, 1976–83 |publisher=Palgrave Macmillan |year=2014 |location=Basingstoke, Hampshire |isbn=978-1-137-44031-0 |oclc=900698250 }}
{{refend}}

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