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A Trident missile armed Vanguard class ballistic missile submarine leaving its base in the Firth of Clyde.

The UK Trident programme is the United Kingdom's Trident missile-based nuclear weapons programme. Under the programme, the Royal Navy operates 58 nuclear-armed Trident II D-5 submarine-launched ballistic missiles and around 200 nuclear warheads on 4 Vanguard-class ballistic missile submarines from Clyde Naval Base on Scotland's west coast. At least one of these submarines is always on patrol as a continuous at-sea deterrent, armed with up to 16 Trident missiles and around 48 nuclear warheads (an average of three warheads per missile), although each submarine can carry up to 160 nuclear warheads with 10 warheads per missile.

'Trident' entered service in 1994. Since the 1998 Strategic Defence Review, the UK's nuclear deterrent is based entirely on submarine-launched missiles, as these are seen as the most reliable method of delivery.



Each of the four Vanguard-class ballistic missile submarines may carry up to 16 Trident II D-5 submarine-launched ballistic missiles (SLBMs), with each missile capable of carrying up to 10 independently targetable nuclear warheads. A 1000-metre aerial trails on the surface behind the submarine to pick up incoming messages. During a patrol the submarine is required to remain silent for three months and is only allowed to make contact with the base in a dire emergency. The submarine navigates using mapped contours of the ocean floor and patrols a series of preplanned "boxes" measuring several thousand square miles. Intelligence is constantly relayed to the vessel, giving details of shipping movements and potentially hostile aircraft or submarines in the area. Most of the crew never know where they are and no-one on board would know which targets were selected.[1] Most of the weapons have a yield of 80-100 kilotons but some are only 10-15 kilotons. Some have multiple warheads and some only have a single small device, as the British prime minister may feel constrained if the response were to be massively disproportionate to the threat.[1] This system is very similar to the US Navy's 14 Ohio-class SSBNs which each carry 24 Trident D5s armed with up to eight W76 or W88 nuclear warheads.


The Trident missile agreement was reached in 1982 as a modification of the Polaris Sales Agreement. At the time it was envisaged the entire project; four submarines, the missiles, new facilities at Coulport and Faslane and a 5% contribution to Trident research and development, would cost £5 billion. The option for a fifth submarine was discussed at the time.

Trident replaced the previous system of 4 Resolution-class submarines each carrying 16 Polaris A3 missiles (known as A3T) with 3 ET.317 warheads (not MIRVed), latter upgraded by the Chevaline programme to A3TK with a limited MIRV capability.

The current Vanguard-class submarines were built at what is now BAE Systems Submarine Solutions in Barrow-in-Furness, Cumbria, the only submarine yard in the United Kingdom. The previous Resolution-class submarines were constructed at Barrow and at Cammell Laird in Birkenhead (now closed).

Trident has been the UK's sole nuclear weapons system since the retirement of the WE.177 tactical nuclear weapon following the 1998 Strategic Defence Review.

UK nuclear policy

The principle of operation is based on maintaining deterrent effect by always having at least one submarine at sea, and was designed for the Cold War period. One submarine is normally undergoing maintenance and the remaining two are in port or on training exercises. The missiles were "detargetted" in 1994 in time for the maiden voyage of the first Vanguard-class SSBN.[2] This means that the warheads are no longer aimed at specific targets but await coordinates that can be received from HQ, programmed into their onboard computers and fired within a 15-minute timeframe. The final decision on firing the missiles is the responsibility of the British Prime Minister, and each holder of this office is required to write a personal letter to the commanders of the four Trident missile-carrying submarines. The letters are locked in the onboard safe on each vessel and, in the event of the submarines irrevocably losing contact with the base due to nuclear war, the decision to fire is handed over to the commander of the submarine.[1] Each submarine carries up to 16 Trident II D-5 missiles, each of which can contain up to twelve warheads (i.e. a potential of 192 warheads); however, the British government announced in 1998 that each submarine would carry no more than 48 warheads total (without indicating how the warheads would be divided among the missiles).[3] While this number is half the limit specified by the previous government, it represents a 50% increase in capacity over the Trident's predecessor, the Polaris A3TK Chevaline.

The United Kingdom has purchased the rights to 58 Trident missiles under the Polaris Sales Agreement (modified for Trident) from a jointly maintained "pool." These missiles are fitted with UK-built warheads and are exchanged when requiring maintenance. Under the terms of the agreement the United States does not have any veto on the use of British nuclear weapons.[4]

While the British government states the warheads used in the UK Trident system were "designed and manufactured in the UK at the Atomic Weapons Establishment (AWE), Aldermaston," declassified U.S. Department of Energy documents indicate the warhead system was involved in non-nuclear design activities alongside the U.S. W76 nuclear warhead fitted in some US Navy Trident missiles.[5] The National Audit Office noted that most of the warhead development and production expenditure was incurred in the US.[6][7] The U.S. President authorised the transfer of nuclear warhead components to the UK between the years 1991 to 1996.[8] This has led the Federation of American Scientists to speculate that the UK warhead may share design information from the W76; a practice which is encouraged by the 1958 US-UK Mutual Defence Agreement.[9]


The total acquisition cost of the Trident programme was £9.8 billion, or £14.9 billion at 2005 prices, 38% of which was incurred in the U.S. In 2005/2006, annual expenditure for running and capital costs was estimated at between £1.2bn and £1.7bn and was estimated to rise to £2bn to £2.2bn in 2007/2008, including Atomic Weapons Establishment costs. Since Trident became operational in 1994, annual expenditure has ranged between 3% and 4.5% of the annual defence budget, and was expected to increase to 5.5% of the defence budget by 2007/2008.[7][10]

The Vanguard submarines which carry the Trident D5 missiles were built with a 25-year life expectancy. Plans have been announced to replace the four vessels as they reach the age of 25 (possibly to be extended to 30) years. Trident's D5 missiles, leased from the USA, are expected to continue in service until at least 2042 following an upgrade. Costs are uncertain, depending on whether the replacement programme buys four completely new-design craft (probably £20bn), modifies the design of the Astute SSN to carry four D5 missiles (uncertain), or simply acquires four new Vanguard class submarines (probably less than £8bn).

It is also uncertain whether the replacement programme will buy three hulls or four. Four hulls would guarantee "continuous at-sea deterrence". Three hulls would present a risk that continuity could be broken.


Test launch of a Trident D5 SLBM

While the theoretical capacity of the four Vanguard-class submarines is 64 missiles and 768 warheads, only 58 missiles were leased and some have been expended in test firings. The UK leases the missiles but they are pooled with the Atlantic squadron of the USN Ohio SSBNs at King's Bay, Georgia[1] (previously the UK maintained its Polaris missiles).

The number of warheads is significantly less than originally intended, due to a changed strategic situation (i.e., the demise of the USSR). Currently there are fewer than 200 warheads, and the number is anticipated to fall close to 160 in near future.

This is also, in part, due to the service pattern. One vessel is always on patrol, one to two are in port or on training exercises and one is undergoing maintenance.

In the Strategic Defence Review published in July 1998, the British government stated that once the Vanguard submarines became fully operational (the fourth and final one, Vengeance, entered service on 27 November 1999), it would "maintain a stockpile of fewer than 200 operationally available warheads."[11] The Stockholm International Peace Research Institute (SIPRI) has estimated the figure as about 165, consisting of 144 deployed weapons plus an extra 15% as spares.[12] Spares are usually needed within the supply chain, including the maintenance workshops.

At the same time, the government indicated that warheads "required to provide a necessary processing margin and for technical surveillance purposes" were not included in the "fewer than 200" figure.[13] However, as recently declassified archived documents on Chevaline make clear, the 15% excess (referred to by SIPRI as for spares) is normally intended to "provide the necessary processing margin" and "surveillance rounds do not contain any nuclear material" being completely inert. These surveillance rounds are used to monitor deterioration in the many non-nuclear components of the warhead, and are best compared with inert training rounds. The SIPRI figures correspond accurately with the official announcements and are likely to be the most accurate. The Natural Resources Defense Council speculates that a figure of 200 is accurate to within a few tens.[14] In 2008 the National Audit Office stated that the UK stockpile was of fewer than 160 operationally available nuclear warheads.[15]


"Trident" is based at HMNB Clyde, in western Scotland. This comprises two facilities, a submarine berth at Faslane and ordnance depot at RNAD Coulport.


According to the British House of Commons' Defence Select Committee, the original purpose of Trident was to discourage aggression against the UK, its allies and its interests from the Soviet Union and the Warsaw Pact.



The Trident system received significant opposition during its development. The most visible opposition has stemmed from the more general use of nuclear weapons, and also from Trident's status under international law. Trident is also seen by some, such as the Scottish National Party, as a sticking point in relations between the Scottish Parliament and Westminster, since the submarines which carry the missiles are based at HMNB Clyde in Scotland.


Several groups have taken action against Trident, including the Campaign for Nuclear Disarmament and Trident Ploughshares, a group set up specifically to oppose the Trident system. In 2006 a year-long protest at Trident's base at Faslane, named Faslane 365, was initiated with the aim of blockading the base every day for one year. As of 26 January, 50 groups had taken part in blockades, leading to 474 arrests.

Trident Ploughshares describes their opposition as follows:

We believe that the use or threatened use of nuclear weapons is totally immoral and irresponsible and that the Trident system is illegal under international law. Our disarmament action is necessary since the UK government has to date shown no signs of any intention to dismantle the system. As citizens we have both a right and a duty to uphold international humanitarian law. The UK’s Trident nuclear weapons system is based on 4 submarines which carry between 12 and 16 missiles, each of which can deliver a number of 100 kiloton warheads to individual targets - mass destruction on an unimaginable level.[16]

Scottish politics

A number of Scottish political parties, such as the Scottish National Party, Scottish Green Party, Scottish Socialist Party and Solidarity, have policies opposing the use of Trident missiles at Faslane in Scotland. Some members and ex-members of those parties, such as Tommy Sheridan, have taken part in blockades of the base there.

In addition to more general anti-nuclear feeling, some see Trident as symbolic of differences in political opinion between Scotland and the rest of the UK - for example, in a major House of Commons vote the majority of Scottish MPs voted against upgrading the system, while a substantial majority of English MPs, Welsh MPs and Northern Irish MPs voted in favour[17].


On 8 July 1996 the International Court of Justice, the highest court of the United Nations, handed down an advisory opinion that stated that the threat or use of nuclear weapons would in most cases violate various articles of international law, including the Geneva Conventions, the Hague Conventions, the UN Charter, and the Universal Declaration of Human Rights.

On 19 December 2005 Rabinder Singh QC and Professor Christine Chinkin, a colleague of Cherie Blair at Matrix Chambers, handed down a legal opinion at the request of Peacerights[18] which specifically addressed

"whether Trident or a likely replacement to Trident breaches customary international law"[19]

Drawing on the ICJ opinion, Singh and Chinkin argued that:

"The use of the Trident system would breach customary international law, in particular because it would infringe the "intransgressible" [principles of international customary law] requirement that a distinction must be drawn between combatants and non-combatants."[19]

In addition, Singh and Chinkin argued:

"The replacement of Trident is likely to constitute a breach of article VI of the NPT...[and that] [s]uch a breach would be a material breach of that treaty."[19]

On 25 January 2007, Des Browne, UK Defence Minister, defended the use of Trident:

"I do not believe it makes sense to say that nuclear weapons are inherently evil. In certain circumstances, they can play a positive role - as they have in the past. But clearly they have a power to do great harm," he said. "Are we prepared to tolerate a world in which countries which care about morality lay down their nuclear weapons, leaving others to threaten the rest of the world or hold it to ransom?"[20]


The British replacement of Trident is a programme replacing the existing Trident weapons system based on four Vanguard class submarines each armed with 16 Trident II submarine-launched ballistic missiles. The government has begun planning a new submarine-based system but there is some opposition to this programme - from those who want to take the opportunity for full nuclear disarmament. Proposals to replace the Trident system were passed by the House of Commons by a majority of 248 on the 14 March 2007.[21] However, the US are extending the life of their Trident submarines to 30–40 years and Professor Richard Garwin, a US nuclear weapons expert and advisor to three US presidents, has advised British MPs that the same could be done in the UK saving £5 billion and allowing time for a rethink of British nuclear strategy. [1]

See also


  1. ^ a b c d e Michael Bilton (2008-01-20). "Dive bombers". The Sunday Times magazine. Retrieved 2009-06-24.  
  2. ^ Trident, Hansard, 11 Jul 2005, Column 662W
  3. ^ Ministry of Defence Fact sheet 4: Current system. From The Future of the United Kingdom’s Nuclear Deterrent
  4. ^ Ministry of Defence, reply to a request about the UK nuclear deterrent
  5. ^ "Stockpile Stewardship Plan: Second Annual Update (FY 1999)" (PDF). U.S. Department of Energy. April 1998. Retrieved 2007-03-15.  
  6. ^ Dan Plesch (March 2006) (PDF). The Future of Britain’s WMD. Foreign Policy Centre. pp. 15. Retrieved 2007-03-15.  
  7. ^ a b Ministry of Defence and Property Services Agency: Control and Management of the Trident Programme. National Audit Office. 29 June 1987. ISBN 0102027889.  
  8. ^ "National Security Directive 61" (PDF). The White House. July 2, 1991. Retrieved 2007-03-15.  
  9. ^ "Britain's Next Nuclear Era". Federation of American Scientists. December 7, 2006. Retrieved 2007-03-15.  
  10. ^ (PDF) The Future of the British Nuclear Deterrent. Research paper 06/53. House of Commons Library. 3 November 2006. Retrieved 2007-03-15.  
  11. ^ "Factsheet 22: Nuclear Deterrent". Strategic Defence Review. July 1998.  
  12. ^
  13. ^ "Written Answers to Questions". Commons Hansard. 14 July 1998.  
  14. ^ NRDC: Nuclear Data - Table of Global Nuclear Weapons Stockpiles, 1945-2002
  15. ^ Ministry of Defence: The United Kingdom’s Future Nuclear Deterrent Capability, National Audit Office, 5 November 2008, ISBN 9780102954364,, retrieved 2008-11-09  
  16. ^ "Introducing Trident Ploughshares". Trident Ploughshares. January 1, 2004.  
  17. ^ BBC News - Scots Labour MPs rebel on Trident
  18. ^ About Peacerights
  19. ^ a b c (paragraph 1 and 2)
  20. ^ "UK must retain nuclear deterrent, says Browne". The Guardian. January 25, 2007.,,1998472,00.html.  
  21. ^ "Trident plan wins Commons support". BBC News. 14 March 2007. Retrieved 2006-04-14.  


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