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A Trident missile launches from a submerged submarine

The Successor programme refers to the replacement of the existing UK Trident programme of submarine-launched nuclear missiles. This would involve replacing the Vanguard class of four Trident ballistic-missile armed submarines with a new class designed to continue a nuclear deterrent after the current boats reach the end of their service lives.[1] The government has begun planning a new submarine-based system[2] but there is opposition from those who want to take the opportunity for full nuclear disarmament or replacement with a cheaper, less capable nuclear weapon delivery system.[3][4] On 18 May 2011 the British government approved the initial assessment phase for the construction of new Trident submarines.

The term "Trident" is widely used to refer to Britain's entire current system of nuclear weapons, including the relevant submarines, missiles and warheads.[1][5] "Trident" is also the shortened name of the system's submarine-launched ballistic missile, the UGM-133 Trident II D-5.



Official policy regarding nuclear weapons is for use as a defensive nuclear deterrent. This refers to the possession of nuclear weapons to deter an enemy nuclear attack with the threat of a retaliatory second strike.

The current reasoning of deterrence is explained in the 1998 Strategic Defence Review (SDR):

We are committed to working towards a safer world in which there is no requirement for nuclear weapons and continue to play a full role in international efforts to strengthen arms control and prevent the proliferation of chemical, biological and nuclear weapons. However, the continuing risk from the proliferation of nuclear weapons, and the certainty that a number of other countries will retain substantial nuclear arsenals, mean that our minimum nuclear deterrent capability, currently represented by Trident, is likely to remain a necessary element of our security.


Since the Manhattan Project produced the first nuclear weapons during World War II, the UK has worked closely with the United States on nuclear strategy. This cooperation was formalised in the 1958 Mutual Defence Agreement (MDA) and has been a key aspect of the special relationship between the two countries.

Trident system

Since the retirement of the last Royal Air Force WE.177 nuclear bomb in 1998, the British nuclear system has been wholly submarine-based. This is intended to deter a potential enemy because they cannot ensure eliminating the entire stockpile in a first strike if a ballistic missile submarine (Ship Submersible Ballistic Nuclear or SSBN) remains undetected.

Since the Strategic Defence Review, the UK has maintained a stockpile of around 200 warheads. In a policy known as "Continuous at Sea Deterrence", at least one Vanguard class SSBN is kept on patrol with up to 16 Trident missiles sharing up to 48 warheads from the stockpile at any given time. The SDR considered this was the minimum number of warheads adequate for deterrence. It is collectively known as the Trident system.[5] The majority of this system is based in Scotland at HM Naval Base Clyde, which includes the Faslane home of the Vanguard submarines, and at the Coulport nuclear depot. The oldest submarine of the Vanguard class is expected to remain in service until 2017[7] without a refit, prompting consideration of a replacement before the end of 2010 to allow for development time.[5]

Replacement system


A December 2006 Ministry of Defence white paper 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 billion based on:

  • £0.25 billion to participate in U.S. Trident D5 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.[2]

These 2006/7 prices would equate to about £25bn in out-turn price for the successor submarines; the 2011 Initial Gate report confirmed estimates of £2-3bn each for the warheads and infrastructure.[8] These cost estimates exclude the Vanguard 5 year life extension and decommissioning, and it is unclear if new Trident missiles will need to be purchased for the life extension programme.[7]

Running costs would be about £1.5 billion per year at 2006 prices.[7]

On 18 May 2011 the British government approved the initial assessment phase for the construction of new Trident submarines, paving the way for the ordering of the first long-lead items and preparations for the main build to begin in the future. The new submarine class will retain the current Trident II missiles,[citation needed] and will incorporate a new 'PWR3' nuclear reactor as well as technology developed for the Astute-class SSNs. The final decision on whether to build the Successor submarines will be taken in 2016[9] and the first boat will be delivered in 2028.[8]

Trident D5 missile life extension

In 2002, the US Navy awarded a contract for the Trident II D5 Service Life Extension Programme to extend the life of the missiles from the mid-2020s to about 2042, to match the extended life of the US Ohio-class submarine. The UK will join this programme to arm a Vanguard submarine class replacement.


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 early 2020s. There are suggestions that the new fleet be cut to three hulls if a Continuous at Sea Deterrent patrol could still be assured at that number. The first SSBN would take 17 years to be designed and built, making a five year life extension of the Vanguard class necessary. On this basis, a refitted Vanguard class could still shrink by at least one vessel before the first replacement SSBN enters service.[2]

Both BAE Systems Submarine Solutions and Rolls-Royce Marine Power Operations are undertaking design studies for the new submarine class.[10] BAE presented two designs at DSEi 2007 labelled Concept 35 and Advanced Hull Form (AHF). Concept 35 is an evolution of the Vanguard-class with influences from the Astute-class.[10] Advanced Hull Form is a less conservative design which, rather than a standard tapered design of the stern, features a Y-shaped stern which houses much of the boat's machinery outside of the pressure hull.[11]

Power plant

In March 2011 a safety assessment of the current Rolls-Royce PWR nuclear power plant design, by the Defence Nuclear Safety Regulator in November 2009, was released under a Freedom of Information request.[12] The Regulator identified two major areas where UK practice fell significantly short of comparable good practice, loss-of-coolant accident and control of submarine depth following emergency reactor shutdown.[13][14] For the replacement submarine the option of developing a new PWR3 plant based on current US design is under consideration, and in March 2011 Defence Secretary Liam Fox indicated this was the preferred option "because those reactors give us a better safety outlook".[15][16] In May 2011 the Ministry of Defence announced that the US design had been selected for the PWR3, at a cost of about £3 billion.[17]


The 2010 Strategic Defence and Security Review concluded that the Successor submarine 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.[8] They would be carried in a 12-missile common missile compartment designed in collaboration with the US for their SSBN-X, which could accommodate the current Trident D5 missiles and any replacement missile once the D5 reaches the end of its expected life in the 2040s.[8]

The remaining warheads are expected to last until the mid-2020s, with a decision to either replace or refurbish them taken closer to that time. The government-owned nuclear weapons research company Atomic Weapons Establishment would likely play a key role in either, with over £1 billion being invested between 2005 and 2008 to maintain "key skills and facilities."[18] The replacement of the Trident missiles was also deferred, as the UK intends to participate in a US programme to lengthen the missiles' lives from the 2020s through to the 2040s.[2]


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."[19] These proposals were motivated by the fact that funding for the Trident renewal programme must now come from the core MoD budget.[20]

The paper outlined four options consistent with the purposes of cost reduction:[21]

  • A ‘Normally-CASD’ Submarine Force: "Under this option, the UK would maintain Trident missiles and submarines, and CASD [Continuous At-Sea Deterrence] would be maintained as normal operating practice. But the MoD would accept an increased risk of short interruptions in CASD in the event of unforeseen, and low-probability, mishaps or accidents."
  • A ‘CASD-Capable’ Submarine Force: "Under this option, the attempt to maintain CASD in normal circumstances would be abandoned, and replaced by an assumption that it would only be necessary to have the ability to reconstitute CASD if required, and then to maintain it for a significant (though not indefinite) period...In order to maintain a credible reconstitution capability, it would be necessary to maintain submarine patrols. But these would not necessarily have to be on a continuous basis."
  • A ‘Dual-Capable’ Submarine Force: "This would maintain the plan to build new submarines, but with only four missile tubes (compared with the twelve currently planned) and with an explicit design mandate that asked designers to allow them also to perform conventional roles...It would not be possible, however, for potential adversaries to detect whether or not a particular boat was nuclear-armed when it went on patrol. Such an arrangement could, in time, combine increased survivability for the nuclear force while also holding out the possibility of further reductions in the size and readiness of the nuclear deterrent."
  • A Non-Deployed Strategic Force: "A more radical option would be to abandon a submarine-based nuclear deterrent altogether, relying instead on a non-deployed arsenal to provide deterrence of future nuclear attacks...The key to an effective UK nuclear deterrent based on this option would be guaranteed, but not prompt, retaliation." Although concluding that "such an option is probably too radical to be politically acceptable at present...It should not be ruled out as a longer-term option, however, perhaps as part of a multilateral agreement to move to lower states of nuclear readiness."

The paper concludes 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."[21]

In July 2013, the British Government published the Trident Alternatives Review.[22] Its findings including:-

  • There are alternatives to the current posture which would enable the UK to inflict "significant damage" and deter aggressors
  • Submarines could potentially be operated at "reduced readiness" when threat levels are lower
  • A continuous-at-sea presence is the most "resilient" posture and guarantees the quickest response
  • Land and air-based delivery systems effectively ruled out
  • An entirely new system, using cruise rather than ballistic missiles, would be more expensive than renewing Trident[23]

Parliamentary support

On 14 March 2007, the Labour government won Commons support for the plans to renew the submarine system. The proposals were passed by the House of Commons by a majority of 248.[24] 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.[24][25] It was the first time MPs had been given the chance to vote on whether the UK should remain a nuclear power, and the biggest backbench rebellion since the beginning of the 2003 Iraq war.[24]

The Labour government decided the final decision to manufacture should be made in 2014.[26]

The new 2010 coalition government agreed "that the renewal of Trident should be scrutinised to ensure value for money. Liberal Democrats will continue to make the case for alternatives." Research and development work continued with an 'Initial Gate' procurement decision, but the 'Main Gate' decision to manufacture a replacement was re-scheduled for 2016, after the next election.[26]

In May 2013 it was reported that Whitehall's forthcoming Alternatives Review had found that land, air or cruise missile systems would be more expensive or more impractical than Trident, and that there would be little saving in reducing from 4 submarines to 3. Cutting to two submarines would cut the capital cost by up to £5bn and save nearly £1bn/year in running costs, but would mean that continuous patrols were no longer possible. The Liberal Democrats, minority partners in the ruling Coalition government, appeared to favour this 2-boat Trident option whilst their Conservative partners preferred the 4-boat option, quoted as costing £20bn.[27] The review found that participating in the US Trident programme was cheaper than starting a UK-only cruise missile programme, previously the Liberal Democrats' preferred option.[27]

Academic review

The Bradford Disarmament Research Centre has received funding from several anti-nuclear organizations, including the Joseph Rowntree Charitable Trust, for a review of the Government's reasons for replacing Trident,[28] aiming "to transform the intellectual agenda on Trident replacement through a detailed and critical examination of the government’s rationales for Trident replacement, a number of crucial issues excluded by the government and the wider implications of the decision, which require a full and balanced."



An anti-nuclear demonstration outside HM Naval Base Clyde


The possession of nuclear weapons, as a form of weapons of mass destruction, has long been criticised in British politics for being immoral, by members of the Campaign for Nuclear Disarmament and their supporters. As such, it has been at the core of the peace movement in the UK since the first introduction of nuclear weapons in the 1950s. The Campaign for Nuclear Disarmament has historically been a significant anti-nuclear lobby group since its formation in 1957. As a result, the potential replacement of Trident has naturally been criticised by the CND, coming under their "Scrap Trident" campaign. More recently in 2006, 20 bishops claimed Trident was "anti-God."[29] Other religious leaders, including former Archbishop of Canterbury Rowan Williams, have questioned the morality of replacing Trident.[30]

Other groups claim the development of new nuclear weapons would undermine Britain's stance with other countries, such as Iran and North Korea, and international nuclear disarmament in general.[31] The UK government insists that there are no plans to enhance the capability of the missiles in terms of payload, range or accuracy, in order to avoid such diplomatic problems.[32]

Strategic value

Another reason cited is the claim that the nuclear environment has become less dangerous since the development of the deterrent during the Cold War. Consequently, with a diminished nuclear threat towards Britain, the value of having a deterrent to guard against it has fallen as well. The Ministry of Defence has a declared policy of sub-strategic use which would see, for example, a limited nuclear strike (e.g. one missile with one limited yield warhead) used as either a deterrent to a country from using chemical or biological weapons or as retaliation for having used them.[33][34][35]

Outspoken critics on this basis include former politicians Denis Healey[36] and Michael Portillo.[37]

Cost and timing

Several groups, such as the Liberal Democrats, Plaid Cymru, Green Party of England and Wales and Scottish National Party and some trade unions, prefer the money to be spent on public services or improved equipment for conventional forces.[4][38] Greenpeace has claimed the recent £1 billion investment in AWE is for secret initial work on developing a replacement.[39]

In evidence to the House of Commons Defence Select Committee on 23 January 2007, the US nuclear expert Richard Garwin said that the plans were "premature and wasteful", and that delaying the decision for 15 years following inexpensive engine repairs would save £5bn. He added that pressure to commission a new fleet of submarines was rooted in the shipbuilding industry's urge to land lucrative contracts.[40]

See also


  1. 1.0 1.1 "Q&A: Trident replacement". BBC News. 11 November 2006. Retrieved 2006-12-01. 
  2. 2.0 2.1 2.2 2.3 "The Future of the United Kingdom’s Nuclear Deterrent". Ministry of Defence. 4 December 2006. Retrieved 2006-12-05. 
  3. "Trident debate to top CND agenda". BBC News. 14 October 2006. Retrieved 2006-12-01. 
  4. 4.0 4.1 "Unions oppose replacing Trident". BBC News. 13 September 2006. Retrieved 2006-12-01. 
  5. 5.0 5.1 5.2 "The Future of the UK's Strategic Nuclear Deterrent". House of Commons Defence Committee. 30 June 2006. Retrieved 2006-12-01. 
  6. "Strategic Defence Review". Ministry of Defence. July 1998. Retrieved 2006-12-01. 
  7. 7.0 7.1 7.2 "The Future of the UK's Strategic Nuclear Deterrent: the White Paper". House of Commons Defence Committee. 7 March 2007. Retrieved 2007-03-15. 
  8. 8.0 8.1 8.2 8.3 "The United Kingdom’s Future Nuclear Deterrent: The Submarine Initial Gate Parliamentary Report". UK Ministry of Defence. May 2011. 
  9. "Daily Hansard - Written Answers". UK Parliament. 18 September 2012. 
  10. 10.0 10.1 "Nuclear options". The Engineer. 2009-01-12. Retrieved 13 January 2009. 
  12. Rob Edwards (10 March 2011). "Flaws in nuclear submarine reactors could be fatal, secret report warns". The Guardian. Retrieved 28 March 2011. 
  13. "Annex B: Successor SSBN - Safety Regulator's advice on the selection of the propulsion plant in support of the future deterrent (4 November 2009)". Successor Submaring Project - Update. Ministry of Defence. 24 November 2009. p. 21. EC-14-02-02-01-14 / Annex B: DNSR/22/11/2. Retrieved 28 March 2011. 
  14. Joseph Watts (11 March 2011). "Expert warned MoD on safety of Rolls-Royce nuclear sub reactors". Derby Telegraph. Retrieved 28 March 2011. 
  15. "Fox wants new reactors for Trident". 15 March 2011. Retrieved 28 March 2011. 
  16. Severin Carrell (23 March 2011). "Navy to axe 'Fukushima type' nuclear reactors from submarines". The Guardian. Retrieved 28 March 2011. 
  17. "PWR3 Reactor chosen for Trident". 18 May 2011. Retrieved 17 June 2011. 
  18. "Written Ministerial Statements". House of Commons. 19 July 2005. Retrieved 2006-12-01. 
  19. "Like for like renewal of Trident will come at expense of conventional forces". Retrieved 2010-09-10. 
  20. "Trident costs must come from MoD budget, Osborne says". BBC News. 30 July 2010. Retrieved 2010-09-10. 
  21. 21.0 21.1 (PDF) Continuous At-Sea Deterrence: Costs and Alternatives. RUSI. July 2010. Retrieved 2010-09-10. 
  22. (PDF) Trident Alternatives Review. UK Government. July 2013. Retrieved 2013-07-19. 
  23. Lib Dems accuse Tories of trying to 'rubbish' Trident report. BBC. July 2013. Retrieved 2013-07-19. 
  24. 24.0 24.1 24.2 "Trident plan wins Commons support". BBC News. 15 March 2007. Retrieved 2007-03-15. 
  25. "Blair wins Trident nuclear arsenal vote". ABC News. 15 March 2007. Retrieved 2007-03-15. 
  26. 26.0 26.1 "Trident: The Initial Gate Decision". Briefings on Nuclear Security. British Pugwash. July 2011. Retrieved 31 December 2012. 
  27. 27.0 27.1 Stacey, Kiran (27 May 2013). "Trident UK’s best option, says review". 
  28. "Bradford Trident Replacement Review Project". Retrieved 2010-07-30. 
  29. "Letters: Nuclear weapons challenge the very core of our faith". The Independent. 10 July 2006. "We write to add our voice to the public debate on the issue of the maintenance and renewal of the Trident nuclear weapons programme" 
  30. "Archbishop questions Trident plan". BBC News. 5 December 2006. Retrieved 2006-12-06. 
  31. "Trident cash risks terror escalation, warns MEP". Green Party. 20 July 2005. Retrieved 2006-12-02. 
  32. "Why do Trident submarines have to be replaced?". BBC News. 15 March 2007. Retrieved 2007-03-19. 
  33. Paul Rogers (July 2006). "Big boats and bigger skimmers: determining Britain’s role in the Long War". Blackwell Publishing. p. 651. Digital object identifier:10.1111/j.1468-2346.2006.00560.x. 
  34. "BBC Breakfast with Frost interview: Geoff Hoon, Secretary of State for Defence". BBC. 2003-02-02. Retrieved 2007-02-02. 
  35. "Weapons of Mass Destruction". Column 8W. Hansard. 2003-10-27. Retrieved 2007-02-02. 
  36. "UK needs no nuclear arms - Healey". BBC News. 2006-07-07. Retrieved 2006-12-02. 
  37. "Scrap UK nuclear arms - Portillo". BBC News. 2005-06-19. Retrieved 2007-03-16. 
  38. "Trident missile costs 'immoral'". BBC News. 28 September 2006. Retrieved 2006-12-02. 
  39. "Nuclear claims over weapons site". BBC News. 23 October 2006. Retrieved 2006-12-02. 
  40. Sample, Ian (24 January 2007). "Trident replacement 'premature'". London: The Guardian.,,1997190,00.html. Retrieved 2007-01-27. 

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