I thought this discussion on British nuclear weapons may be of interest to EA Forum members. 
 

A British Vanguard-class submarine showing the strain from a nuclear deterrent patrol.

Britain has fielded nuclear weapons for more than seventy years, but today its ability to sustain an independent deterrent is more uncertain than at any point since the 1950s. Britain maintains operational control over its nuclear deterrent, but the current submarine delivery system is ageing rapidly and increasingly overstretched. The recent failures of two consecutive missile tests, with subsequent trials not scheduled for years, call into question whether Britain’s nuclear posture is sustainable and credible. The submarines tasked with providing the nuclear deterrent have been running patrols far beyond their intended duration, placing extraordinary mechanical strain on the boats, resulting in punishingly long tours for submariners. Despite these challenges, every major political party remains committed to sustaining the continuous at sea deterrent, or CASD, into the 2030s and beyond.

Beneath the surface, however, Britain has quietly dismantled the industrial and technical base needed to independently design warheads, enrich uranium, or build missile delivery systems. It is entirely dependent on US technology, materials, and expertise to maintain every component of the deterrent, from targeting software to tritium supply. As Washington increasingly prioritises China over Russia, British nuclear strategy risks drifting into irrelevance: tied to a superpower whose strategic focus is moving elsewhere, and sustained by a supply chain the UK no longer controls.

The price of a special relationship.

After closely working with the United States on the Manhattan Project to deliver an atomic bomb, in the wake of the Atomic Energy Act of 1946, which prohibited the sharing of nuclear research and technologies, Britain was left without atomic weapons and a long road to developing theorised thermonuclear bombs. The British Government at the time decided to pursue this new marker of a first-rate global power despite the diminished status of the British Empire in the years following the Second World War, spending £100 million (roughly £3.5 billion today) to successfully detonate a 25 kiloton atomic bomb in October 1952. This was a significant financial burden, equivalent to around 0.5% of GDP at the time, and the Ministry of Works complained that post-war reconstruction was being slowed to allow Britain to develop atomic weapons. Less than a month later, the US detonated a 10.4 megaton device, demonstrating the power of thermonuclear bombs, leaving the UK to play catch-up again, which it announced it had achieved in November 1957 by successfully detonating a hydrogen device. The Government was knowingly lying about the yield of the bomb (it had only been 0.3 megatons), but it successfully helped persuade the US to reconsider cooperating with the UK on nuclear research, design, and testing. As the US was concerned about Soviet advances in missile and nuclear technologies and was stunned by the Sputnik satellite, the attitude towards cooperation with another Western power had changed considerably since 1946, allowing a financially stretched and technically limited British role in American nuclear technology. The genesis of the current British nuclear weapons arsenal and its posture, including the decision to maintain nuclear submarine-launched ballistic missiles on a continual patrol, is rooted in the 1958 US–UK Mutual Defence Agreement.

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A 1957 British hydroden bomb test.

When British politicians talk about how the US is its closest ally, despite plenty of evidence to suggest the US favors other countries such as Israel, France, Japan, or Saudi Arabia more, it is the Mutual Defence Agreement that gives that claim substance. The UK is the only country with which the US shares nuclear warhead designs, submarine propulsion technologies, ballistic missile systems, enriched uranium and tritium stockpiles, and nuclear test data. The closest comparable deal is the AUKUS agreement between the UK, Australia, and the US, which is limited to sharing resources and designs on nuclear submarines, not nuclear weapons. Without the MDA between the UK and US, it is highly questionable whether the UK would be able to maintain its current nuclear status.

The current British nuclear arsenal consists of around 220 nuclear weapons in the form of “British-designed” Mk4/A Holbrook (by the Atomic Weapons Establishment at Aldermaston, although they are effectively copies of the W76 US weapons) thermonuclear warheads, which each have an estimated yield of 100 kilotons. Although these are significantly less powerful than some of the weapons developed by the US and Soviet Union in the Cold War, the Trident II D5 missile (which can be fired at targets up to 2,500 kilometres away and at its fastest can travel at more than 20,000kph), which delivers the Mk4/Holbrook weapons, carries 3-5 warheads under current plans, but can carry up to 12. These warheads can independently target different locations when the missile is in space. Trident missiles are carried on the Vanguard-class ballistic missile submarines, and under current doctrine, they carry eight Trident missiles, although they can hold up to 16. At least one boat (the traditional term for a submarine in the US and Royal Navies) is always on Operation Relentless, the Royal Navy’s name for continual at sea deterrent (CASD) patrols. Although the nuclear posture is “purely defensive”, the British government has remained deliberately ambiguous about the situations in which it would consider using nuclear weapons, refusing to adopt a “No First Use” policy to maintain the possibility in an adversary's mind that a nuclear attack could be launched first. British nuclear weapons are not only retained to deter an “extreme” (meaning chemical, biological or nuclear attack) against the UK itself, but are also assigned to the defence of its NATO allies. Whether Britain would actually use nuclear weapons in response to an attack on a NATO member is debatable, as is the question of whether Britain would use nuclear weapons if it were not joining the US in deploying them.

Unlike the US, which has engaged in publicly threatening nuclear weapons usage numerous times, including against China in 1955, and in 1991 handed a letter to Iraqi Foreign Minister Tariq Aziz with the words “this is not a threat, but”. The UK has only once done this publicly, echoing American threats against Saddam Hussein to potentially retaliate with nuclear weapons if chemical or biological weapons were used against coalition troops. Despite British possession of nuclear weapons not deterring the Argentine invasion of the Falklands, the task force that sailed to liberate the Falkland Islands in 1982 did contain tactical nuclear weapons on board the aircraft carrier HMS Hermes. Britain was then and remains committed to not using nuclear weapons against non-nuclear states. Currently, Britain cannot threaten to use smaller, tactical nuclear weapons as it only has the Trident missile system to deliver strikes.

The effects of a 100-kiloton nuclear bomb on London.

Britain is the only nuclear-armed country to have a single deterrence system. Britain adopted a minimum credible deterrent at the end of the Cold War, retiring its air-launched WE.177 tactical nuclear weapons carried by the RAF in 1998, having already removed nuclear depth charges, Vulcan strategic bombers, and US-supplied Lance ground-launched missiles as tensions dropped in the early 1990s. Even North Korea technically has two delivery systems, with the primary method being ground-launched Hwasong ballistic missiles, and shorter-range KN series missiles, and the Pukguksong series submarine-launched system providing further options. France, the closest comparable nuclear power to Britain, maintains submarine-launched ballistic missiles (the M51 missile built by Ariane Group) and the Air-Sol Moyenne Portée cruise missile (built by MBDA) designed to be carried by Dassault Rafale fighter jets, which could be theoretically delivered from jets operating from the French aircraft carrier, Charles de Gaulle.

The Vanguard submarine class, Trident missiles, and Mk4/Holbrook warheads are currently being replaced as the Vanguard boats continue to deploy on CASD patrols far beyond their design life of 25 years. This brings risk, and by the time the Dreadnought replacement is in service, some Vanguard boats will be 38, 39, or 40 years old. When the previous generation of Resolution-class SSBNs came towards the end of their service lives, they began to fail sea trials due to the years of mechanical stress operating in the most hostile environment on earth, and only two boats (HMS Resolution and HMS Repulse) were able to carry out increasingly long patrols at shallower depths. Although the plans to deal with a “worst case scenario” of moving a CASD submarine into Loch Long, where it would dive and remain in a static location, reportedly never came to pass, this suboptimal situation is now being seen again on the ageing Vanguard boats, and in some ways is much worse.

The unprecedented 107-day patrol conducted by a Resolution-class boat seems quaint to the grueling patrols that submariners are now expected to conduct to maintain CASD with the Vanguard class, as patrols are averaging 163 days, and one boat was at sea for 204 days in 2024. The Vanguard class was designed to be at sea for 90-120 days on an operational patrol, and on these longer patrols, it has been reported that submariners were forced to ration the remaining food. There are now questions around if the boats are surfacing to be resupplied with food, which would mean there are in fact periods of time where the nuclear deterrent is not actually available. Surfacing also means the submarine is liable to be detected, violating the fundamental command objective: always remaining undetected. It is so important to stay undetected that prior orders in the event of a life-threatening medical episode were to deal with the incident on board (including potential surgery conducted by the ship's medical officer) and to place a deceased sailor in the deep freezer rather than surface to seek help. If CASD patrols are surfacing for resupply, this undermines the deterrent, and if the alternative is to ration food, morale and retention in the submarine service will continue to suffer.

British submariners are volunteers within a volunteer service. An uncertain amount of time spent away from family, friends, and normal life, with no internet access, little exercise space and no fresh air for more than six months at a time is exchanged for an average of 5% higher wages than serving in the surface fleet and perhaps a personal thank you from the Royal Family, senior politicians and defense staff. The Royal Navy, like the other services, is seriously struggling to recruit (in 2023, the HMS Raleigh training establishment had just 109 recruits out of a capacity of 375) and retain sailors. The demands of the CADS place significant burdens on the submarine services' 830 officers and 3,150 ratings, and although major maintenance and teething issues have been reported, resulting in the Astute class attack submarines not taking to sea (none were sailing at times in 2024), it is possible that men are being pulled from attack boats to meet the crewing requirements of the CASD missions, particularly engineers and nuclear technicians.

The Vanguard class has ended up in this position due to years of delays in deciding to replace them, the decision to rip out HMS Vanguard's nuclear reactor (this was supposed to take three years costing £200 million but predictably took seven and cost over £500m), and unfortunate timing and delays in refitting the other boats in the class. To cap these issues of age, manpower difficulties, and increasingly long patrols, the most credible threat to the deterrent is the public failure of the last two Trident missile tests from British submarines.

A failed Trident missile test in 1986. Photos of the British 2024 have not been released.

Trident missiles for the British nuclear deterrent are shared in a pool with the US Navy, which deploys Trident on its 14 Ohio-class SSBNs, and are primarily stored at Naval Submarine Base Kings Bay in Georgia, USA. Around 40-60 missiles drawn from the pool are then transported to the Missile Servicing Facility at Coulport to be loaded onto Vanguard boats. Although day-to-day inspections of missiles at Coulport are handled by British personnel, if there are major servicing or maintenance issues, these are dealt with by the USN Strategic Systems Program back in Georgia. Trident missiles are designed and built by the prime contractor, Lockheed Martin. Every year, a Trident missile is fired from a submarine to test both the missile, submarine and her crew, and as a partner, the Royal Navy tests on rotation. In January 2024, the missile failed to ignite its first stage booster and unflatteringly “plopped” into the sea next to HMS Vanguard carrying the First Sea Lord and Defence Secretary. This followed a 2016 test conducted by HMS Vengeance saw the missile veer off course and have to self-destruct. Trident has been tested 215 times by the United States and the UK in total, including eight failures, five of which occurred between 1987–89, leaving the overall failure rate at 2.6%, but the consecutive failures of British tests raise questions about whether ageing British submarines have a specific issue with Trident, which has been upgraded multiple times since their introduction. Obviously, if there is such an issue, it will not be publicly acknowledged, but the UK is reliant on the US Navy and defense companies to fix the problems.

The British nuclear strategy is intrinsically tied to the US position against its Cold War adversary, the Soviet Union. The dependency on the US, while both countries were primarily concerned with the Soviet nuclear threat, made the cost of maintaining the deterrent justifiable. However, as the US focuses on the military and economic threat posed by China, a British deterrent aimed at deterring Russia while tied to the US, which may not be so concerned with wanting to risk nuclear war with a secondary threat, means the credibility of British nuclear weapons is weakened. Although there is a limited but realistic possibility of China and the United States going to war, and a route within that to a nuclear exchange, it is hard to envision how severely weakened British military forces would be able to fight alongside the US in the South China sea given the political reality that China is very far away. Dealing with the economic and social upheaval such a war would bring would be a major political challenge and increase the chances of a Russian attack on British European allies. The idea of Britain launching nuclear weapons against China in the event of a US/Chinese nuclear exchange and inviting Chinese nuclear retaliation is very remote. As British and US military threats diverge in the future, although Britain has operational control over its nuclear weapons, it is doubtful if Britain can realistically threaten to launch or retaliate to a Russian attack if the US does not approve, making the whole arrangement increasingly strategically incoherent.

Operational Independence, Total Reliance

The justifiable questionability of the credibility of the British nuclear deterrent has to be placed into the context of the cost of maintaining it, the financial burden it places on the rest of Britain's armed forces and the total reliance on the US for every part of the system. Currently, the UK is paying a publicly disclosed figure of around £3 billion annually (6% of the defense budget) to maintain the Vanguard class in a ring-fenced allocation. Prior to 2010, the cost of providing for the deterrent was met by the central government's special reserve budget, and the prediction by some that moving this to the Ministry of Defence's budget would hollow out conventional forces has proven to be correct. Although not the only factor, since 2010 the Royal Navy has seen its surface combatants decrease from 23 to 16, and of those 16 ships, only a handful are deployed on operations or being used in training. The Royal Navy cannot provide a full escort for its aircraft carriers and is reliant on allies to provide ships for the planned 2025 Carrier Strike Group deployment to the Pacific Ocean (Norway is providing a frigate and fleet oiler, while Canada and Spain are both providing a frigate for significant parts of the operation).

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The current Dreadnought-class SSBN program (HMS Dreadnought is currently being constructed at BAE Systems in Barrow in Furness) is expected to cost £31 billion/$41 billion to bring the boats into service without delays or cost overruns, with an additional £4 billion cost to develop the A21/Mk7 or Astraea warhead and an estimated £4 billion (not including maintenance) to purchase Trident II D5LE2 missiles. However, only parts of this acquisition program are currently funded, and the National Audit Office estimates a £7.9 billion deficit as things currently stand. If reports about the nuclear program eating up any spare cash are accurate, and combined with the need to replace missile stocks sent to Ukraine, the recent announcement that defense spending will rise is meaningless in delivering visible new capabilities.

The Dreadnought class is the least dependent part of the whole deterrent system on US technical and material support, relying principally on the Common Missile Compartment housing the Trident missiles and US-developed software for elements of targeting, fire control, and system diagnostics. The UK designs and builds its own submarines (BAE Systems) and nuclear reactors (Rolls Royce in Derby), and although the UK does have a store of highly enriched uranium for nuclear submarine reactors, this was all produced before 1995 and the most critical components of the deterrent system are reliant on US supply chains. Britain stopped enriching uranium partly due to its existing stockpile, the cost of maintaining the plant at Capernhurst, and a desire to commit to non-proliferation ambitions. Since then, three nations (India, Pakistan and North Korea) have developed nuclear weapons, undermining the wisdom of this desire. In 2024, the defense secretary announced that Britain would explore options for reestablishing a domestic fuel cycle capability. However, currently the UK is dependent on the US for additional HEU requirements, as restarting enrichment of uranium would incur significant costs (an enrichment plant, conversion and feedstock infrastructure, fabrication and handling facilities, security, licensing, and commissioning would be over £10 billion) and take up to ten years, particularly with byzantine British planning laws and the ability of activists to raise legal challenges. The re-conversion of the plant at Capenhurst would also violate international law, as it is legally required only to produce material for civil infrastructure, a significant blocker as the current Prime Minister, Sir Keir Starmer, was himself a human rights lawyer and worked to strengthen international law during his career before formally entering politics.

Additionally, the integration of the Common Missile Compartment and the accompanying software makes it impossible for the UK to move to another missile delivery system without totally redesigning the Dreadnought class and costing billions. It would also require designing its own submarine-launched ballistic missiles, which is theoretically “possible” as MBDA UK does have some technical expertise, but realistically there is no British space program or credible space company that could work on this effort. Furthermore, the French M51 missile is not designed by MBDA France and cost over €10 billion to develop. It could be possible for Britain to request that MBDA be involved in the design and production of Trident II D5LE2 missiles to build a more robust and sovereign capability, but this would be dependent on the goodwill of President Trump and his successor. Arguably, developing a more substantial British missile industry would be in line with President Trump’s and Vice President Vance’s ambition to reduce European military dependence on the US, but this would mean a smaller workshare for Lockheed Martin and may spook US officials who fear the UK may in the longer term seek its own credibly independent nuclear weapons program.

The UK is heavily reliant on the United States for the supply of tritium (used in nuclear weapons to increase the efficiency and explosive power of warheads), and while it possesses its own stockpile of plutonium for warhead production, it no longer has the capacity to produce new fissile material and would depend on US support to maintain or expand its arsenal over the long term. There is a facility under construction in Oxfordshire to recover and recycle tritium for civilian use, which is unlikely to be able to service military needs. Tritium has a relatively short half-life of 12.3 years, which means it decays over time and needs to be replenished regularly. The US itself is struggling to produce tritium, as it closed its Cold War manufacturing facility in 1988 and only opened the tritium production facility at Watts Bar Unit 1 in Tennessee in 2003. The production facility has consistently failed to meet production expectations, only producing 1/10th of the expected supply.

Britain was a world leader in plutonium production from the 1950s until it stopped production in the late 1960s with a significant stockpile, enough for 3-400 warheads. Its large (139 tons) civilian plutonium stockpile is mostly unsuitable for military use, although it could be theoretically refined further. In practice, the UK relies on the US for further material when needed. If the UK decided to restart plutonium production and avoid the concerns of the international community, it would likely cost billions to build or repurpose a facility. The attempted U.S. MOX (Mixed Oxide Fuel Fabrication Facility) at Savannah River serves as a recent example of how even financially well-resourced and technically capable states struggle with plutonium production, as the project was closed down after $8 billion was spent.

British dependence on US technical assistance, materials, and designs is deeply apparent in warhead design. The current “independently designed” Mk4/Holbrook warhead is so similar in design to the US W76 warhead that the British warhead is part of the W76 maintenance program, and the minutes of the second meeting following the signing of the 1958 MDA suggest that American scientists provided the blueprint. Furthermore, after the announcement of the development of the US W93 warhead, the British defense secretary lobbied the US Congress for funding for the A21/Mk7/Astraea, one of the only examples of Britain asking for direct US military financial aid since the Second World War, suggesting the US costs of developing the W93 which the UK is expected to copy are too expensive. This reliance also suggests that the UK has not actually designed a nuclear weapon since the introduction of the WE.177 tactical nuclear bomb in 1966. If you were 18 years old and working at AWE on the WE.177 during its design, you would be 77 years old. Although Britain does have the blueprints for the W76 and will be gaining close proximity to the W93, it is debatable if Britain actually has the capacity to design a nuclear weapon on its own, unlike France, which designs its own weapons under the direction of the Direction des Applications Militaires (DAM and developed the Tête nucléaire océanique (TNO) warhead in 2015.

A Dassault Rafale fighter jet carrying the Air-Sol Moyenne Portée cruise missile.

A further issue with the credibility of the A21/Mk7/Astraea is that as the UK and US are signatories to the Comprehensive Nuclear-Test-Ban Treaty (CTBT) this new warhead will not be live tested to demonstrate it works. Although the US has not ratified the CTBT, and testing could resume under US law (and very likely would if Russia or China resumed nuclear testing), the W93 and its British derivative are reliant on subcritical testing, computer simulation, and component tests to demonstrate the devices work. While this may satisfy internal concerns about the credibility of the warheads, there will continue to be doubt in the minds of potential adversaries about whether these weapons work. For the US, this is less of an issue as it will continue to maintain warheads and designs which were tested, but the UK is acquiring a sole deterrent that has never been live tested. In a currently unlikely but conceivable scenario where the 1958 MDA is dissolved and the UK has A21/Mk7 warheads as its only nuclear weapon, without US technical support on maintaining them or access to the stockpile of missiles in Georgia, the British nuclear deterrent would be the least credible in the world. Developing a sovereign nuclear deterrent would take years and cost tens of billions of pounds, and although the UK has some of the necessary ingredients for such a program, it arguably would be in a worse position than non nuclear Japan or South Korea, both of which possess space programs, independent missile manufacturers, large civillian nuclear programs, and larger manufacturing and talent bases. Both of these countries could develop nuclear weapons in as little as 6-12 months, although the cost would be in the tens of billions of dollars. In contrast, nuclear-armed Britain has effectively outsourced its entire nuclear deterrent to the US, at a time when global tensions are rising and nuclear-armed countries and stockpiles are increasing.

Although Britain would face significant political, economic, and diplomatic costs to develop its own nuclear weapons, it could acquire US designs for warheads delivered by air-launched missiles flown by F-35 or the proposed Tempest fighter jet. It would not be cheap, and would stretch limited British plutonium and tritium stockpiles, but it would provide an additional capability which may be more usable than submarine-launched strategic weapons on ageing submarines. It would not solve the deeper problems of reliance on the US for its nuclear weapons for decades, but moving to a more normal standard of multiple delivery systems for nuclear weapons would enhance the fear for adversaries that Britain can use nuclear weapons to defend its European NATO allies.

Conclusion - Is it worth it?

Overly optimistic decisions made at the end of the Cold War regarding future threats, leading to a degradation in military preparedness, industrial base and energy security, have unfortunately led to a deeply troubling situation for Britain in the 2020s. As Russia has demonstrated its willingness to attack its neighbour in Ukraine, China is rapidly increasing its nuclear stockpile, and the UK's closest ally pays more attention to disputes in East Asia, Britain has both severely underprovisioned conventional military forces and has abandoned its ability to develop nuclear weapons. The strategic decision to rely on a single deterrent system means the only conceivable short-term way to increase the options available to military planners would be to purchase US-designed air-launched warheads. Only over a much longer period of time will the UK be able to rebuild a truly independent nuclear deterrent.

With the cost of maintaining CASD and developing its replacement, the UK is spending a minimum of £6/$7.9 billion a year on its nuclear weapons program, over 10% of the whole defense budget. Britain has underfunded its military for decades, poorly chosen to fight non-essential conflicts which have cannibalized planned equipment purchases and managed its existing procurement projects woefully. Despite the spending on the deterrent arguably being better spent on rebuilding its conventional forces, the political consensus behind maintaining the illusion of an independent nuclear capability and fear of jeopardising the relationship with the US means it is deeply unlikely Britain will abandon its operational nuclear deterrent, despite the costs. If the US decides in the future to withdraw troops and its military underwriting of European countries, the current British nuclear program will severely limit strategic choices available to political elites.

The current model is strategically incoherent. Without a reassessment of what a credible British deterrent actually requires, Britain will be paying tens of billions for decades for weapons it can never realistically use and will weaken military forces that would serve a deterrent purpose. Britain clings to the symbols of great power status, but if the country wants to be taken seriously as a nuclear power by Russia, China, France and the US, it must confront the uncomfortable reality that it no longer is one and act accordingly.

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