Trident, Vanguard and Successor: A Guide to the British Deterrent

As the date of the main gate decision on "Trident" edges ever closer the debate on the UK's nuclear deterrent has intensified. Heated arguments have flown back and forth between those who see renewal as necessary and those who disagree strongly with it on ethical, financial and practical grounds. While it's a positive sign that the debate has been conducted in the public sphere, to a much greater extent than most defence issues, there remains a great deal of misinformation and confusion surrounding the specifics and the terminology of "Trident" renewal. Unfortunately, while there are a few exceptions, the reporting of defence issues by the major public outlets is often patchy, biased and sometimes downright inaccurate. In this piece I hope to address the specifics of the system colloquially known as "Trident" and provide the facts (along with some context) on renewal, along with some of my own views on the key issues and misconceptions that surround the nuclear deterrent. Rather than engaging in the moral arguments surrounding nuclear weapons this piece is purely designed to address the technical issues, as well as some of the less than accurate public and media perceptions of the deterrent.

The Vanguard Class:

Britain's nuclear weapons are currently carried aboard the four submarines of the Vanguard class, operated by the Royal Navy. The entered service between 1993 and 1996 and are the largest submarines operated by the UK. At just under 16,000 tons submerged they're roughly twice the size of the Astute class nuclear powered attack boats and three times the size of the older Trafalgar class submarines. Each boat has a compliment of ~135 Officers and Ratings, but has twice that number assigned to it, forming two full ships companies referred to as the "port" and "starboard" crews. This ensures that the deterrent boat will never be prevented from sailing due to illness or injury amongst critical members of the team needed to run the boat, as there are always spares available. While one crew is deployed the other will either be on leave or in training. In order to provide "Continuous At Sea Deterrence" or CASD the four submarines rotate, with one armed and deployed in an undisclosed location, one in training and preparing to deploy, one undergoing short term repairs and one in deep refit. In this way there has always been one nuclear-armed British submarine at sea at all times since patrols began in April 1969. Following on from their predecessors the Vanguard class operate from HM Naval Base Clyde, sometimes referred to as Faslane.

The Vanguard Class are officially referred to as SSBNs (which stands for Ship, Submersible, Ballistic, Nuclear) meaning that they are not only powered by a nuclear reactor but also carry nuclear-armed ballistic missiles. The class are powered by the Rolls Royce PWR2 nuclear reactor, enabling the submarines to remain underwater for months on end, limited only by food supplies for the crew. Each Vanguard class submarine can carry up to sixteen Trident II D5 ballistic missiles. However, due to the UK's participation in multilateral arms reduction since the end of the Cold War they're now believed to routinely sail with only eight. The Vanguard class also carry conventional torpedoes for self-defence against other submarines and surface ships. Construction of the four Vanguard class submarines cost the UK around £15 billion, just over £1 billion a year spread over twelve years from the keel of the first boat being laid in 1986 to the completion of the fourth and final boat in 1998. Although the boats have an expected lifespan of twenty five years, a substantial life-extension programme will enable them to serve an additional ten to ensure a seamless transition from the Vanguard class to the "Successor" submarine class.

Key Issues and Misconceptions:

-Although the mainstay of Britain's nuclear deterrent has been provided by "Continuous At Sea Deterrence" for almost a half century now, some believe the operation of the four deterrent submarines imposes a serious burden on the Royal Navy. Of the roughly 4,000 Officers and Ratings of the submarine service around a quarter or more are likely assigned to the deterrent submarines. In addition a frigate, attack submarines and submarine hunting aircraft are needed to protect the deterrent boat as it enters and leaves the Royal Navy's base on the Clyde.

-Some commentators have described the CASD system as a leftover from the Cold War, unsuited to a world where Terrorism and cyber warfare will become the real threats in future. However, with an increasingly aggressive Russia modernising its own nuclear forces, others would suggest that the system still remains relevant to today's problems as well as providing insurance against unexpected future threats. While both arguments have some merit, it is interesting to note that all other nuclear powers either possess, are renewing or are pursuing a submarine-based deterrent. The broad perception abroad seems to be that submarine-launched ballistic missiles are both relevant and a credible means of deterrence.

-While it has been claimed that the boats might be vulnerable to some form of cyber attack it is doubtful that this is actually the case. The deterrent submarines operate a closed computer system, so any would-be attacker would have to actually get on-board and introduce such a computer virus manually. The development of software that could attack the submarine's vital systems would also require in-depth knowledge of the system in the first place, something that a hostile state or terrorist group would find all but impossible to acquire. Even then, as with most RN vessels, the submarine will have manual and analogue back-up systems should the computerised primaries fail. All told it would be almost impossible to conduct a successful cyber attack on the existing nuclear deterrent submarines.

-In the last few years there have also been a spate of articles expressing concern about the safety of the submarines, citing hundreds of accidents as well as tens of fires, equipment failures and "nuclear incidents" on board as evidence of a profoundly unsafe system. However, taken at face value and without any context these figures can be extremely misleading. For example: while it's true that fires occasionally occur on all Royal Navy warships, almost all are extinguished within seconds of breaking out. Even in the event of a serious fire, the Royal Navy rightly maintains some of the highest standards in the world when it comes to firefighting and damage control (having thoroughly learned the lessons of the Falklands War). As for "nuclear incidents", none of the twelve "Category B" events that have occurred since 2009 threatened the release of nuclear material into the environment or atmosphere. Nor did they endanger workers or the public. As it stands, a Category B incident is defined as: "actual or high potential for a contained release [of radiation] within building or submarine or unplanned exposure to radiation". According to the Ministry of Defence, most of these incidents were minor.

-There is also a misconception amongst some less well informed observers that because all UK submarines are "nuclear" they all carry nuclear weapons. This is not the case, Britain currently operates two separate types of submarine: the four nuclear armed SSBNs of the Vanguard class and the seven nuclear powered but conventionally armed SSNs (Ship, Submersible, Nuclear) of the Astute and Trafalgar classes. While all UK submarines are powered by a nuclear reactor, only the four boats of the Vanguard class carry ballistic missiles and nuclear weapons.

The "Successor" Submarines:

The "Successor" submarine is intended as the replacement for the existing Vanguard class, with the first boat expected to enter service in 2028. The class is expected to have a service life of around thirty years, with the fourth boat likely to operate well into the 2060s. Unlike the Vanguard class the Successor will have four fewer ballistic missile tubes, a total of twelve rather than the Vanguards' sixteen. These tubes will be a shared design with the US Navy, who are looking to start replacing their Ohio Class ballistic missile submarines within a similar time frame. Each "Common Missile Compartment" will contain four launch tubes, Successor will have three such compartments, whereas the American SSBN-X (their next generation ballistic missile submarine) will have four or more. This will enable the UK and US to pursue a common replacement for the Trident II D5 missile when it goes out of service in the 2040s. As it stands the government's current intention is to maintain the number of missiles (eight) and warheads (forty) carried by the Vanguard submarines with the transition to Successor. In 2011 it was agreed that the Successor submarines would use the Rolls Royce PWR3 reactor, an "Anglicised" version of the US Navy's latest design. The new reactor is expected to be safer and cheaper to maintain over the boats' thirty year lifespan, when compared with the PWR2 that currently powers the Vanguard and Astute classes.

As it stands, little concrete information exists in the public sphere beyond relatively broad specifications and a few concept images (like the one shown above). However, from historical precedent and educated guesswork we can safely assume that the Successor boats will be significantly quieter than their predecessors, just as the Astute class are markedly quieter than the Trafalgar class that came before them. Like the Vanguard class they will also carry conventional torpedoes for self-defence. It seems unlikely that the relatively successful dual-crew system would not be carried over to the new deterrent submarines.

Key Issues and Misconceptions:

-A few people have also claimed that the ballistic missile submarine will soon be made obsolete by underwater drones, and other unmanned systems, that can listen for and detect submarines and unmanned aircraft that are currently being developed. They argue that the Successor class would be hopelessly vulnerable to such systems, as it would lose its ability to hide. These commentators forget that these technologies are far from new, during the Cold War NATO erected vast arrays of fixed hydrophones to detect Soviet submarines in the North Atlantic, and certainly not foolproof. With every generation submarine detection equipment has become more sensitive, yet the boats continue to get quieter in response. Each measure developed to detect the submarine is met with a countermeasure in response. Not only have the boats changed beyond all recognition since their primitive beginnings at the turn of the twentieth century, but so have the tactics employed to hide them. Examining the lessons of history it seems unlikely that a single innovation in anti-submarine warfare will, at a stroke, render the submarine obsolete.

-There appears to also be a presumption that the Successor submarines are extremely expensive, as they form the biggest chunk of the expenditure necessary for the renewal of the UK's nuclear deterrent. There is also a perception that the programme costs have increased significantly since it was first announced in 2007. However, much of the apparent increase in the cost of replacement has been due to inflation. The 2006 defence white paper on the issue laid down an estimated price of £15-20bn for the whole nuclear renewal programme,most of which would be the cost of the new submarines. When adjusted for GDP inflation to match 2014 prices the "cost" rises to between £17.5 and 23.5bn for the whole programme. While the higher figure closely matches the "between £20 and 30bn" price-tag stated by the government, it may also have been stretched to encompass costs previously not included, such as through-life expenditures, decommissioning and safe disposal of the boats and their nuclear reactors. On top of this the Treasury has added a £10bn contingency fund, the purpose of which is somewhat opaque; but could conceivably be the government hedging against a second Scottish referendum (and the need to reconstruct facilities elsewhere) or simply prudent management to ensure the delivery of a critical defence equipment programme.

-There is also a view that the cost of the Successor submarines, the major expense involved in renewal of the nuclear deterrent, could easily be transferred to bolster the UK's conventional forces that have been run down over a long period of time. However, upon close examination of the issue the issue is far more complex than many realise. Firstly the shortfall in work for the nuclear submarine construction facilities at Barrow in Furness would have to be made up with a substantial order of more Astute class nuclear-powered attack submarines. Likely more than five boats costing £750 million each, so many more conventionally armed submarines would likely impose through-life costs and crew requirements similar to the nuclear deterrent boats that they would replace. It is likely that we would eventually end up having to build two classes of conventionally armed, but nuclear-powered, submarines in order to sustain the design and industrial base necessary to continue producing attack submarines. The cost of safely decommissioning the nuclear weapons facility at Coulport would also be very substantial and eat into any short-term savings made. Also to be considered is that, in the event of Trident cancellation, some or all of the money saved would inevitably be siphoned off by the Treasury and redirected into other areas of government (as many anti-nuclear figures argue should be the case) such as: health, education, welfare etc... It is by no means clear that cancelling the successor submarines would lead to a substantial re-investment in conventional forces and would almost inevitably impose significant second-order costs. While long-term savings would indeed be made, it would not be the panacea for either conventional defence, or other areas of government spending, that some make it out to be.

The Trident II D5 Submarine Launched Ballistic Missile:

The UGM-133 Trident II, or Trident II D5, is a Submarine Launched Ballistic Missile (SLBM) with a range of more than 7,500 miles and a payload of up to twelve nuclear-armed Multiple Independently-targetable Re-entry Vehicles (MIRVs). The missile first entered service with the US Navy in 1990 and later with the Royal Navy in 1993 when the first of the Vanguard class submarines entered service. Unlike conventional and cruise missiles the Trident II D5 leaves the earth's atmosphere for part of its trajectory, acting like a multi-stage rocket, before its warheads return to earth and strike their targets. The missile is principally guided by an on-board astro-inertial guidance system, that can be supplemented by GPS to increase its accuracy. From what is publicly available this system takes account of the submarine's relative position to its target and uses a fixed object (in this case a star) as a reference point to guide the missile onto its target. At present the UK leases 58 of these missiles from the United States, which are drawn from a common pool shared by the US Navy's Atlantic SSBN squadron. Unlike its predecessor, Polaris, the missiles are not serviced in the UK but at the Lockheed Martin plant in King's Bay Georgia along with the US Navy's missiles. 

Key Issues and Misconceptions:

-While the recent discussion on the subject of the British nuclear deterrent has been framed as the renewal, or replacement, of Trident; in fact the Trident II D5 missile is set to remain in-service with the Royal Navy and US Navy into the 2040s. It is one of the few components of the overall system that, while it will receive a substantial life extension, will not be replaced for many years to come.

-Often the most contentious arguments over the UK deterrent relate to its independence from the United States, specifically the degree of operational control that the Americans could exert over the British system. Firstly, it is necessary to clearly state that the US do not possess a "kill switch" that would render the UK's missiles inert or would prevent them from being fired. As the US Navy's own missiles are of the exact same design, drawn from the same pool as the UK's, such a safeguard (if it existed) would therefore also render a major component of their own deterrent useless. Nor does the US government possess the ability to remotely destroy the missiles once launched, such a system would open their own deterrent up to being disabled by a potential enemy, should they steal the means of "self-destructing" the missiles. The system is designed so that, short of being actively shot down, once released the missiles cannot be stopped. There is also the suggestion that the US could simply "turn off the GPS", even if it were as simple as those that claim this make out; disabling the GPS would simply make the missiles marginally less accurate. Their primary means of guidance, the astro-inertial star sight system, is designed to function without input from GPS. The retention of this older system is likely deliberate, as it prevents the US/UK deterrent from being disabled by an attack on the American GPS satellite network. While the US could withhold gravitational data and weather reports over the intended target area, this would simply degrade the accuracy of a British nuclear strike and would not be able to prevent it. For all intents and purposes the UK deterrent is Operationally Independent: meaning that the US have no means to stop the UK from conducting a nuclear strike, short of shooting down the British missiles.

-With respect to the independence of the system it is true that should the US decide to withhold access to its missile servicing facilities it could eventually render the UK's Trident II D5 missiles unusable. According to Parliamentary estimates his would likely take many months, if not a year or more, to achieve. However, given the UK's extremely close relationship with the United States and the existing unprecedented level of co-operation in the field of nuclear weapons and delivery systems the chance of this actually happening would best be described as extremely remote. At the least it would require a severe political break between the UK and US, significantly worse than that which occurred during the Suez Crisis. In the author's opinion, this remains extremely unlikely and the US will almost certainly remain a highly dependable partner in this field. This is not least because the joint submarine deterrent using the Trident missile strengthens the American nuclear guarantee of Europe significantly. Fundamentally it ensures that a potential enemy could not tell a British attack from an American one, this means that Britain could force a general nuclear exchange with the United States if the US were to renege on its commitment to the defence of Europe during a crisis. This inextricably ties the American strategic deterrent to the defence of Europe, something the US are very much aware of and value.

-There have been plenty of commentators keen to express the obsolescence of the Trident missile system, describing it as a "Cold War relic" designed to destroy Moscow and St Petersberg. While there is a grain of truth at the heart of this argument, it too is misleading. The British deterrent was, at the time of the Cold War designed around the so-called "Moscow criterion". In short this was the requirement that the British delivery system be able to penetrate the defences around the Soviet capital and conduct a successful nuclear strike against it. Initially this meant that the RAF's V-bomber force was equipped to break through Soviet air defences in order to reach their targets. However, as Soviet defences improved it became clear that air-launched weapons (even primitive cruise missiles like the RAF's Blue Steel) would not be sufficient. So the UK turned to submarine launched ballistic missiles: first Polaris, then an improved version of Polaris codenamed "Chevaline" and later Trident. These improvements all ensured the UK could respond to aggression with an assured response, capable of penetrating even the most sophisticated integrated air and missile defense system in the world. The "Moscow criterion" remains relevant because, if the UK can be sure of its ability to carry out a successful nuclear response against the most heavily defended target in the world, then it can be sure of a successful nuclear response anywhere else. This strengthens the deterrent power of the overall system, because crucially it remains highly credible in all circumstances.

The W76 Nuclear Warhead:

After the retirement of the RAF's remaining WE.117 air-dropped nuclear bombs in 1998 the W76 became the only warhead in service with the UK armed forces. It is believed to be an "Anglicised" copy of an American design, although the details of its internal components are mostly classified. What is known is that the warhead sits within the conical Mk. 4 re-entry vehicle (a mock-up of which is pictured above). With a declared maximum yield of 100 kilotons of TNT the W76 is around seven times more powerful than the Atomic bomb dropped on Hiroshima at the end of the Second World War. However, some sources indicate that the UK's possesses weapons with a variable yield, down to as low as 10 kilotons, in order to provide decision makers with a more flexible and proportionate nuclear response (if such a thing exists). Between one and twelve warheads can be carried by each Trident II D5 missile. It is believed that the 40 deployed warheads are spread unevenly amongst the eight missiles carried aboard the deterrent submarine. These are believed to be mixed with dummy warheads, decoys and penetration aids in order to ensure the success of a UK strike conducted against an area protected by a sophisticated missile-defence system.

The UK's warheads are designed and manufactured at the two Atomic Weapons Establishment (AWE) facilities at Aldermaston and Burghfield. There is a high degree of collaboration with the US' counterpart facilities at the Los Alamos site in New Mexico and the Sandia & Lawrence Livermore laboratories in California. The UK's weapons are also stored at the Royal Naval Armament Depot (RNAD) at Coulport, which is jointly run by a subsidiary of AWE and Lockheed Martin, where they are mated with the Trident II D5 missiles and loaded onto the deterrent submarines. Although the UK continues to refuse to release the exact details of its nuclear arsenal, it is believed to possess a total stockpile of 225 weapons, with around 160 of those being operational at any one time.

Key Issues and Misconceptions:

-Some have questioned the independence of the UK's deterrent on the grounds that the AWE uses a number of "off the shelf" components, procured from the United States, in Britain's nuclear weapons. According to a report submitted to Parliament these include: the firing mechanism, Neutron generator, gas reservoir and Mk. 4 re-entry vehicle. While it is true that Britain would find it difficult to immediately source replacements if the US chose to withhold these components, it would be well within the UK's capacity to manufacture them. As the AWE possesses the full designs for the W76 warhead, creating native versions of certain components wouldn't be prohibitively difficult; if the commitment was made to continue with the deterrent under such circumstances. However, as with the withholding of support for the UK's Trident II missiles, the likelihood of the US actually doing this remains extremely remote.

-There have also been questions raised, notably in Parliament, about the possibility of dangerous nuclear emissions from RNAD Coulport. According to data released by the Ministry of Defence emissions were well within the safety limits set by both the MoD and the Scottish Environment Protection Agency (SEPA) between 2009 and 2012. For comparison, in 2012 the Hunterston B civil nuclear power station discharged around 370 times the Tritium gas of RNAD Coulport, while still being within the safe limits set by SEPA. The emissions from the nuclear storage facility can be considered so small in comparison as to be negligible, posing no health risk to those living on or around the facility.

-Also of concern to some is the vulnerability of the UK's nuclear weapons to seizure by terrorists, especially considering that they're transported by road between AWE Aldermaston and RNAD Coulport. However, it must first be stated that successfully intercepting and seizing a warhead from one of these convoys would require a level of intelligence gathering and combat capacity beyond any militant group currently operating on the British Isles. Not only are the times and routes of these convoys national secrets of the highest order, revealed only to regional police forces hours before the convoy moves through their jurisdiction, but they are also extremely heavily guarded. Not only does each convoy have a range of civilian emergency teams to deal with any contingency, from safety experts to firefighters, but it is guarded by armed Ministry of Defence Police officers of the Special Escort Group, and likely also special forces personnel. Each convoy is continuously tracked by the police and is in constant radio communication with support forces should an incident occur. Successfully plotting an attack on one would be nearly impossible, something reserved more to the pages of a Tom Clancy novel than reality.

-Some may also worry that the weapons themselves are inherently unstable and dangerous, threatening to trigger a nuclear explosion at any moment should somebody make a mistake. This is categorically not the case, the bomb itself is built to do a very specific thing: evenly compress the core of nuclear material (likely highly enriched Plutonium in the case of the W76) until it reaches the critical point at which a chain reaction occurs and causes a "nuclear explosion" as we know it. In order to achieve this, the device uses explosives precisely placed around the core, and crucially: detonated at the same instant. On two occasions during the early years of the Cold War US aircraft armed with nuclear weapons crashed, unevenly detonating the explosives in their nuclear weapons. Instead of causing a nuclear explosion it merely shattered the core and spread toxic plutonium dust over a small area. Even in the worst-case scenario, a nuclear weapon exposed to the extreme shock of an air crash followed by an explosion, the weapons didn't explode. Unlike some conventional explosives nuclear material will not explode if dropped, burned or exposed to an uneven explosion. Thankfully nuclear weapons are almost impossible to inadvertently detonate.


There you have it, a reasonably examination of the technical details of the UK nuclear deterrent, addressing some of the issues raised in the recent debate and some of the popular misconceptions about the UK's nuclear forces. Hopefully by collecting a broad range of information in one place I can help contribute, in some small way, to improving a debate which is too often mired in inaccurate perceptions.