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

This article covers the entire British Trident nuclear weapons programme. For a technical discussion of the Trident I and Trident II missiles, see Trident (missile)

The UK Trident programme encompasses the development, procurement and operation of the current generation of British nuclear weapons, and the means to deliver them. Trident itself is an operational system of four Vanguard-class submarines armed with Trident II D-5 ballistic missiles, able to deliver thermonuclear warheads from multiple independent re-entry vehicles. It is the most expensive and the most powerful capability of the British military forces.

Operated by the Royal Navy and based at Clyde Naval Base on Scotland's west coast, at least one submarine is always on patrol to provide a continuous at-sea deterrent. Under the terms of the 2010 Strategic Defence and Security Review,[1] each will be armed with a maximum of eight missiles and 40 warheads, although their capacity is much larger.

The UK Trident programme was announced in July 1980, and patrols began in December 1994. Since 1998, Trident has been the only British nuclear weapon system in service. Its stated purpose is to provide "the minimum effective nuclear deterrent as the ultimate means to deter the most extreme threat."[1]

Trident replaced the earlier submarine-based Polaris system, which was in operation from 1968 to 1996. Work on a potential replacement for the Trident system has begun, although no final decisions have been taken.


Trident was first agreed by Prime Minister Margaret Thatcher and US President Jimmy Carter.

In 1980 the British government announced its intention to replace its independent nuclear deterrent, and formally sought permission to acquire the Trident I C-4 missile then in service with the US Navy.[2]

Trident would replace the Polaris system of four Resolution-class submarines, equipped with the US-built Polaris A3 missile. These missiles were originally armed with triple ET.317 warheads aimed at a single target, later upgraded by the UK Chevaline programme to two hardened warheads accompanied with countermeasures.[3]

Following the acceleration of the US Trident II D-5 programme, the existing Polaris Sales Agreement was modified in 1982 to permit the supply of the more advanced missiles.[4] Under the agreement, the UK would lease 65 Trident II D-5 missiles from a larger pool of such weapons based at Naval Submarine Base Kings Bay in the United States. The US would retain responsibility for the maintenance of the missiles, and the UK would manufacture its own warheads and submarines.[5]

The entire project was projected to cost £5 billion, including the four submarines, the missiles, new facilities at Coulport and Faslane and a five per cent contribution to Trident II D-5 research and development. The option for a fifth submarine was discussed at the time but later discounted, and the number of missiles leased was later reduced from 65 to 58.[6]

The UK programme's future was secured the following year when the Conservative government won the general election, defeating the Labour opposition which had pledged to cancel the programme.[7] The Vanguard-class submarines were built between 1986 and 1998 by Vickers Shipbuilding and Engineering at Barrow-in-Furness, Cumbria. The first British Trident missile was test-fired from HMS Vanguard on 26 May 1994, and Vanguard went on to begin the first Trident patrol in December of that year. According to the Royal Navy, at least one submarine has always been on patrol ever since.[8]

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.[9]

UK nuclear policy

The UK Trident programme was initiated during a period of increased tension known as the Second Cold War, and its capabilities were designed to deter powerful Warsaw Pact forces. By the time of the first Vanguard patrol in December 1994, the Soviet Union no longer existed and UK nuclear policy was gradually adjusted during the following years.[5]

The final decision on firing the missiles is the responsibility of the British Prime Minister. Upon taking office, the Prime Minister is required to write four identical letters of last resort which are locked in a safe aboard each submarine. In the event of irrevocably losing contact with the UK, the commanding officer must follow the instructions in the letter if he believes that the United Kingdom has suffered an overwhelming attack.[10] The content of the letters is not disclosed, but the orders may include launching a devastating retaliatory strike.

Under the terms of the missile lease arrangement, the United States does not have any veto on the use of British nuclear weapons, which the UK may launch independently.[11]

Cold War policy

The programme was designed to deter aggression from the Warsaw Pact.

The Trident system was designed to provide an ongoing independently-controlled deterrent against major threats to the security of the United Kingdom and NATO.[2] At the time, these threats were perceived to come from the Soviet Union and its Warsaw Pact allies.[5] To provide an effective deterrent, the system was intended to "pose a potential threat to key aspects of Soviet state power" while remaining invulnerable to surprise or pre-emptive attack.

As with Polaris, Trident would be owned and operated by the UK but committed to NATO and targeted in accordance with plans set out by its Supreme Commander in Europe. The system would be used independently only if "supreme national interests" required it.[12]

The independent deterrent was seen as necessary in case the Soviet Union believed that it could threaten nuclear attack on Western Europe without the risk of US retaliation, because of US fears of a Soviet counter-strike against its own population centers.[2] Without a credible US umbrella, European leaders would be susceptible to nuclear blackmail which could force them into major concessions.[13]

It was considered crucial that the independent British deterrent could penetrate existing and future Soviet anti-ballistic missile (ABM) capabilities. A powerful ABM system, the ABM-1 Galosh, defended Moscow and NATO believed that the USSR would continue to develop its effectiveness. The deterrent logic required the ability to credibly threaten the destruction of the Soviet capital and other major cities.[5] The expensive Chevaline upgrade to Polaris had been designed to keep pace with the ABM developments, but the full MIRV capabilities of the Trident missiles were deemed necessary to assure the credibility of the deterrent into the late 1990s and beyond.[2]

Post-Cold War policy

Test launch of a Trident D5 SLBM

The USSR collapsed in 1991, and NATO military posture was relaxed. Trident's missiles were "detargetted" in 1994, ahead of the maiden voyage of the first Vanguard-class SSBN.[14] This means that the warheads are no longer aimed at specific targets but await coordinates that can be programmed into their on-board computers and fired within 15 minutes.

Although designed as a strategic deterrent, the more unstable world that emerged after the Cold War[citation needed] led the government to conclude that a sub-strategic (but not tactical) role was required. The 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.” On 19 March 1998 Defence Secretary George Robinson 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.”[15]

The government announced in 1998 that each submarine would carry no more than 48 warheads, and further reduced this to a maximum of 40 warheads split between eight missiles in 2010.[16]

Design, development and construction

Trident required the design and construction of four very large submarines, the development, testing and assembly of a new generation of warheads, as well as the construction of new shore facilities. This work began in 1980 and the first patrol took place in late 1994. Submarine production continued until 1998, and it is believed that new warheads are still being assembled at a trickle rate. In addition, the UK government provided five per cent of the costs towards the development of the Trident II D-5 missile.[17]

Vanguard-class submarines

A starboard quarter view of HMS Vanguard arriving in port.

The Vanguard class submarines were designed and built at Barrow-in-Furness by Vickers Shipbuilding and Engineering, now BAE Systems Submarine Solutions. The Devonshire Dock Hall was built specifically for the construction of the submarines. The missile compartment is based on the system used on the American Ohio class, although with capacity for only 16 missiles, rather than the 24 aboard an Ohio boat.

The 'Vanguard' submarines were designed from the outset as nuclear-powered ballistic missile platforms able to accommodate the Trident II D-5. This required the boats to be significantly larger than the previous Resolution class, and they are some of the largest submarines ever built, only eclipsed by the American Ohio and Russian Typhoon- and Borei-classes.

In addition to the missile tubes, the submarines are fitted with four 21 inch (533 mm) torpedo tubes and carry the Spearfish heavyweight torpedo[18] allowing them to engage submerged or surface targets at ranges up to 65 kilometres (40 mi; 35 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 require further re-fuelling for the rest of their service lives.[19]

Prime Minister Margaret Thatcher laid the keel of the first boat, HMS Vanguard, on 3 September 1986.[20] The fourth and final boat, HMS Vengeance, was launched on 19 September 1998.


The British government maintains that the warheads used in the UK Trident system were "designed and manufactured in the UK at the Atomic Weapons Establishment (AWE), Aldermaston". However, declassified US Department of Energy documents indicate that development of the non-nuclear elements of the warhead may have taken place alongside those of the US W76 nuclear warhead fitted in some US Navy Trident missiles.[21]

The National Audit Office noted that most of the warhead development and production expenditure was incurred in the US.[22][23] The US President authorised the transfer of nuclear warhead components to the UK between 1991 and 1996.[24] This has led the Federation of American Scientists to speculate that the UK warhead may share design information from the W76; a practice encouraged by the 1958 US-UK Mutual Defence Agreement.[25]

Nine joint US/UK underground nuclear tests were carried out at the Nevada Test Site between 1983 and 1991,[26] with many or all of these believed to be tests of the British-variant Trident physics package.[27]

The final warheads have been assembled at the AWE facilities near Aldermaston and Burghfield since 1992, and are transported to storage facilities in Scotland by heavily-guarded overland convoys.[28]

Trident II D-5 Missiles

An unarmed Trident II D-5 is test launched from the USS Nevada

UGM-133 Trident II D-5 is a submarine-launched ballistic missile, built by Lockheed Martin Space Systems in Sunnyvale, California, and deployed with the US Navy as well as the Royal Navy.[29] The British government contributed 5% of its 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 the USS Tennessee in March 1989. The launch attempt failed because the plume of water following the missile rose to greater height than expected, resulting in water being in the nozzle when the motor ignited. Once the problem was understood relatively simple changes were very quickly made but the problem delayed the Initial Operational Capability of Trident II until March 1990.[30]

Trident II D-5 was designed to be more sophisticated than its predecessor Trident I C-4, and have a greater payload capacity. It is accurate enough to be used as a first strike weapon. All three stages of the Trident II D-5 are made of graphite epoxy, making the missile much lighter than its predecessor.[31]

By February 2012, there had been 137 consecutive successful test flights since 1989, and the first test from a British Vanguard-class submarine took place in 1994.[32]

The missile has a range of 11,300 kilometres (7,000 mi), a top speed of over 13,422 mph and a CEP (accuracy) of less than 120m. The missile uses an inertial guidance system combined with star-sighting, and is not dependent on GPS.


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.[23][33] Each missile costs nearly £17mn.[34]

Various studies have put the cost of the programme much higher – according to Greenpeace, replacing the program would cost £34bn,[35] while the upkeep of the system over its 30-year life could run up to £130bn.[36] According to the BASIC think tank, cancelling the program would save the budget over £83bn over the next 50 years.[37]

Trident system in operation

The Trident system is made up of 58 leased Trident II D-5 missiles, four native Vanguard-class ballistic missile submarines and 160 operational thermonuclear weapon warheads, together with command-and-control and other supporting infrastructure.

Each of the submarines can carry up to 16 Trident II D-5 submarine-launched ballistic missiles (SLBMs), with each missile capable of carrying up to 12 independently targetable nuclear warheads. This makes for a potential maximum of 192 warheads per submarine. The current loading is unknown, although the 2010 Strategic Defence and Security Review set out that in the future each submarine would be armed with 8 missiles and a maximum of 40 warheads.

Most of the warheads have a yield of 80-100 kilotons, although there has been speculation that some missiles may be armed with a single low-yield nuclear warhead of 10-15 kilotons.[10][38]


The principle of operation is known as continuous at-sea deterrence, which means that at least one submarine is always on active patrol. A second submarine is normally undergoing maintenance and the remaining two are in port or on training exercises. During a patrol, the submarine is required to remain silent for three months and is allowed to make contact with the base only in a dire emergency. The submarine navigates using mapped contour lines of the ocean floor and patrols a series of planned "boxes" measuring several thousand square miles. A 1000 metre aerial trails on the surface behind the submarine to pick up incoming messages. 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.[10]

Command and control

The Prime Minister's command bunker is located beneath the Ministry of Defence in Whitehall, London

Only the Prime Minister or a designated survivor can order the missiles to be fired. These orders would likely be issued from the Pindar command bunker under Whitehall in central London. From there the order would be relayed to the CTF 345 operations room at the Northwood Headquarters facility in Hertfordshire, the only facility allowed to communicate with the Vanguard commander on patrol. 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 weapons engineering officers. At the end of the Cold War, the US Navy installed devices to prevent rogue commanders persuading their crews to launch unauthorised nuclear attacks. These devices prevent an attack until a launch code had been sent by the Chiefs of Staff on behalf of the President. The UK took a decision not to install equivalent devices onto Vanguard on the grounds that an aggressor might be able to eliminate the British chain of command before a launch order had been sent.[39][40][41]

The process by which a Trident submarine would determine whether the British government continues to function includes, amongst other checks, establishing whether BBC Radio 4 continues broadcasting.[42] If the UK Government no longer functions, the letters of last resort drafted by the Prime Minister would be retrieved from a safe bolted to the control room deck.

Missile and warhead inventory

Flag display at Strategic Weapons Facility Atlantic, King's Bay, Georgia

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-class SSBNs at King's Bay, Georgia[10] (previously the UK maintained its Polaris missiles). The pool is 'co-mingled' and missiles are selected at random for loading on to either nation's submarines.

The number of warheads is significantly less than originally intended, due to the changed strategic situation after the demise of the USSR. Currently there are fewer than 200 warheads, and the number is anticipated to fall close to 160 in the near future. 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."[43] 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.[44] 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.[45] 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.[46] In 2008 the National Audit Office stated that the UK stockpile was of fewer than 160 operationally available nuclear warheads.[47]


Location of Faslane and RNAD Coulport.

"Trident" is based at HMNB Clyde, in western Scotland. This comprises two facilities, a submarine berth at Faslane near Helensburgh, and an ordnance depot at RNAD Coulport. Faslane was chosen at the height of the Cold War because of its position on the deep and easily navigable Gare Loch and Firth of Clyde. This position provides for rapid and stealthy access through the North Channel to the patrolling areas in the North Atlantic, through the GIUK gap to the Norwegian Sea. Coulport is used to store the warheads and provides loading and unloading facilities.

In addition, repair, refuelling and refit of the Vanguard class submarines is carried out at HMNB Devonport near Plymouth.


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.

Former Vulcan squadron commander and current vice-president of CND Air Commodore Alastair Mackie has referred to Trident as Britain's 'stick-on hairy chest'.[48]

Scottish politics

All major pro-independence Scottish political parties, such as the Scottish National Party, Scottish Green Party, Scottish Socialist Party and Solidarity, have policies opposing the presence of the Trident system in Scotland. Some members and ex-members of those parties, such as Tommy Sheridan, have taken part in blockades of the base at Faslane.

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.[49]

In the event of a successful vote for independence in 2014, a future Scottish Government may no longer be willing to host Trident. This would lead to a loss of around 520 jobs directly dependent on the submarine facility on the Clyde. Pro-Union parties have been criticised for overstating the scale of job losses should this happen.[50]

In April 2013, thousands of Scottish campaigners, MSPs, and union leaders, rallied against nuclear weapons. The Scrap Trident Coalition wants to see an end to nuclear weapons, and says saved monies should be used for health, education and welfare initiatives. There was also a blockade of the Faslane Naval Base, where Trident missiles are stored.[51]


Police dismantling a blockade of protestors at the Faslane base.

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. By 26 January 2007, 50 groups had taken part in blockades, leading to 474 arrests.

Trident Ploughshares describe 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 four 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.[52]


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[53] which specifically addressed

"whether Trident or a likely replacement to Trident breaches customary international law"[54]

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."[54]

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."[54]

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?"[55]


The Vanguard-class submarines were built with a 25-year life expectancy, taking them into the 2020s. The Trident II D-5 missiles are expected to continue in service until at least 2042 following an upgrade.

The government has begun planning a new submarine-based system, and has announced its intention to replace the four vessels as they reach the age of 25 (possibly to be extended to 30) years. Costs are uncertain, depending on whether the replacement programme buys new-design boats, modifies the design of the existing Astute class SSN to carry ballistic missiles, or simply acquires new Vanguard-class submarines. A final decision to proceed with the replacement has not yet been taken. It is also uncertain whether the replacement programme will buy three submarines or four. Four submarines would guarantee "continuous at-sea deterrence". Three submarines would present a risk that continuity could be stretched. The proposed 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 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.[10]

There is some opposition to the replacement programme - both from those who want to take the opportunity for full nuclear disarmament and those, such as the Liberal Democrats who would prefer a less costly alternative. Initial proposals to replace the Trident system were passed by the House of Commons by a majority of 248 on 14 March 2007.[56]

See also


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  53. About Peacerights
  54. 54.0 54.1 54.2 (paragraph 1 and 2)
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