Conflict and Leadership
Global Britain? Why Is the UK Increasing Its Nuclear Stockpile and What Does This Mean?

The decision to increase the cap on nuclear warheads marks an abrupt departure from a generation of previous UK disarmament initiatives and advocacy. Andrew Futter, Professor of International Politics, University of Leicester, discusses why it was taken now.

On 16 March, as part of its Integrated Review of Security, Defence and Foreign Policy, the UK government announced that it would be increasing the maximum number of nuclear warheads kept in its stockpile. This surprising announcement follows nearly three decades of nuclear reductions and disarmament advocacy by the UK, and could see the total number of nuclear weapons rise from approximately 225 today up to 260 in the years ahead. A more challenging and evolving global security environment, including new technological and doctrinal threats, and it seems concerns about advances in the ballistic missile defence (BMD) systems deployed by possible adversaries, has been cited as the reason for this shift. However, this announcement appears unlikely make a significant difference to UK nuclear deterrence capabilities or to “nuclear stability”, and may prove counter-productive to the new post-Brexit “Global Britain” brand.

The UK and nuclear weapons

The UK has taken progressive steps to reduce its nuclear weapons capability since the 1980s, and has roughly halved the total stockpile of nuclear warheads since the end of the Cold War. In 1998 it retired the free-fall nuclear bombs that could be delivered by aircraft, and under plans laid out in 2010, the stockpile was due to be reduced to a maximum of 180 warheads by the mid-2020s, of which 120 would be “operationally available”. In addition to this, for the past decade, it is believed that the maximum number of nuclear warheads deployed on the UK’s nuclear-powered submarines has not exceeded 40 (in theory each of the current Vanguard class SSBNs could carry a maximum of 192 warheads: 12 warheads on each of 16 missiles).

The current UK nuclear warhead, known colloquially as the “Holbrook”, is believed to be a boosted fission or thermonuclear device with a maximum yield of 100kt, which shares a number of similarities with the US W76 nuclear warhead. UK nuclear warheads are constructed and maintained at the UK Atomic Weapons Establishment at Aldermaston and Burfield, and sit atop Trident D5 intercontinental-range Submarine Launched Ballistic Missiles (SLBMs) that are built and maintained in the US. The UK leases these missiles from a “common pool” shared with the United States; they are loaded onto UK submarines at Kings Bay, Georgia. The missiles are carried by four Vanguard-class nuclear powered submarines which were built at Barrow-in-Furness in the north of England. The UK currently has four of these submarines, one of which is always armed and on patrol as part of a policy of continuous-at-sea-deterrence (CASD). These submarines are based at HM Naval Base Clyde in Scotland.

The UK is currently in the process of building a new fleet of four submarines to be known as the “Dreadnought class” to replace the current fleet by the end of this decade. Interestingly the new Dreadnought submarines will have a reduced missile-carrying capability and have 12 rather than 16 missile tubes. In a similar timeframe the UK will need to replace the aging Holbrook nuclear warhead: estimates suggest that this will take more than decade to design, build and eventually deploy. The UK hopes to develop this new warhead in parallel with the US development of its own new W93 warhead (though it is unclear how dependent the UK is on the US). The Trident D5 missile has been given a life extension programme that will keep it in service until the 2040s.

Explaining the decision

The decision to increase the cap on nuclear warheads marks an abrupt departure from a generation of previous UK disarmament initiatives and advocacy, and raises the question of why now? The Integrated Review places the global threat environment at the heart of the reason for this shift in nuclear policy, but this becomes more complicated upon closer inspection.

This is because it is unclear how a small increase in the overall stockpile of warheads enhances the deterrence equation vis-à-vis possible adversaries and threats.

The UK is committed to deploying a minimum credible, independent nuclear deterrent capability, that is “effective against the full range of state nuclear threats,” and a declaratory policy that is “deliberately ambiguous, about when and how nuclear weapons might be used.” The less verbalised requirement is the so-called “Moscow criterion”, effectively the ability for UK nuclear weapons to be able to inflict unacceptable damage on an adversary, even one protected by BMD. For three decades successive UK governments have believed that this could be achieved with with a reduced number of nuclear warheads. It is difficult to see a compelling strategic rationale to change this now, and this suggests the influence of other factors.

Four in particular stand out. First, the need to increase the total nuclear stockpile could be driven by the fact that some nuclear warheads that have been retired and are waiting to be dismantled, are not technically “unusable” yet. When the new warhead is inducted, this could take the total number above current levels. Second, it might be related to precautions being taken to ensure that the future crossover between inducting new nuclear warheads into the UK stockpile and retiring old ones runs smoothly. Third, the small increase might be part of the lobbying process to ensure that the US Congress agrees to fund the new W93 warhead, upon which the next generation UK warhead will be based. The US already funds two SLBM warhead programmes, and therefore the need to replace is less urgent than it is for the UK. A fourth possibility is that the nuclear aspect of the Integrated Review has been used to draw attention away from what has been perceived as cuts to conventional forces, and even to bolster the status and resolve of Global Britain as a nuclear power.

Strategic, military and political implications

The strategic and military implications of the decision to increase the maximum number of warheads in the nuclear stockpile seems likely to be limited. For comparison, a total stockpile of 260 would move the UK marginally further ahead of India and Pakistan (~150 apiece) and Israel (~80), be considerably more than North Korea (~20), slightly closer to the stockpiles held by France (~300) and China (~290), but still a long way away from those held by the world’s two leading nuclear powers, the United States (~5500) and Russia (~6370).

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It is unclear how a handful of extra warheads would make much difference against for example the BMD systems that Russia or China might be able to deploy in the next few years. Stealthier, more manoeuvrable and better protected warheads surrounded by decoys, (as seems likely with the new warhead being developed), should be sufficient without an overall increase in numbers. If there is a genuine concern about BMD and other capabilities that might undermine the UK nuclear deterrent, then more drastic changes might be needed: more submarines, better underwater protection, or even different delivery systems for example. This doesn’t appear to fit with UK plans for the new Dreadnought class submarines to carry fewer missile tubes than the current Vanguard class fleet (albeit the new warhead might be smaller and lighter, which potentially means more on each missile).

Likewise, it is difficult to see how increasing the cap on nuclear warheads can provide the UK with more military options, especially sub-strategic. The current and future warheads will probably have variable nuclear yields, but any use would immediately give away the position of the submarine making it vulnerable to attack (and thus potentially undermining any further deterrence value it might have). It is possible the UK could “surge” two submarines to sea during a crisis to complicate this for an adversary, which might necessitate more operational nuclear warheads, but there is no guarantee that two boats would be ready and available to do this.

The announcement is likely to have political ramifications. Domestically, in the UK it draws attention back to the wisdom of spending billions of pounds on nuclear weapons at a time when the economy has been ravaged by the coronavirus pandemic. Internationally, the decision will make for awkward questions at the forthcoming Non-proliferation Treaty (NPT) Review Conference, provide more ammunition for supporters of the Nuclear Ban Treaty, and complicate any future arms reduction discussions between the other nuclear powers.

Nuclear weapons and Global Britain

The decision to marginally increase the cap on UK nuclear warheads may make little strategic or military difference to UK capabilities or to our nuclear world order, but it is easy to see how it might be commingled with the notion of a post-Brexit “Global Britain”. Whether this is a deliberate ploy on behalf of the British government or a smoke screen for the practicalities of remaining in the “nuclear club” is a moot point, but the subtle political impacts are likely to be more negative than positive for the UK in the years ahead.
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Views expressed are of individual Members and Contributors, rather than the Club's, unless explicitly stated otherwise.