Going Ballistic: The UK’s Proposed Nuclear Build-up

HMS Vengeance returning to HMNB Clyde, after completing Operational Sea Training. Courtesy of POA Tam McDonald/Ministry of Defence

The most significant change in the UK’s nuclear posture in decades is controversial and has still not been properly debated in parliament.

The UK today announced the most significant change to its nuclear weapons posture in at least two decades. The Integrated Review, a much anticipated reassessment of strategic policy that reaches far beyond nuclear issues, states that the UK is raising a self-imposed limit on its overall nuclear warhead stockpile, abandoning a previous cap of 225 warheads as well as the current reduction target of 180 by the mid-2020s, and replacing it with a new cap of 260 warheads. Just as importantly, the UK will no longer place a public limit on the proportion of that stockpile that is operational at any given time (which had previously been set at 120 warheads), nor will it give any public information on the number of warheads and missiles deployed on its ballistic missile submarines (which had previously been set at no more than 40 and 8 respectively).

This reverses the UK’s course of consistent post-Cold War nuclear reductions and runs counter to previous assurances that the programme to replace the UK’s existing nuclear deterrent would not add to the number of nuclear warheads in service. It is also in apparent contrast to the review’s emphasis on UK support for multilateral diplomacy, and will do much to negate a self-crafted diplomatic image of the UK as the most progressive of the world’s nuclear-armed powers.

These changes are presented as a reaction to a changed international security environment, and the government paints a picture of a world with growing international competition and increasing threats from Russia, China, North Korea and Iran. In its judgment, UK adversaries are increasing the variety and quantities of their nuclear capabilities, and see nuclear weapons as a means of coercion, deterrence and even warfighting. There is no formal move away from the central UK concept of a minimum, credible, assured nuclear deterrent, but the government’s decision indicates a belief that this minimum deterrent can grow as well as shrink, if that is what is required for it to remain credible. It also indicates that credible nuclear deterrence is more important to this government than its disarmament commitments.  

Analysts have in recent days proposed reasons other than national security for this policy shift, but none of these explanations alone explains the scale and detail of the change. Some observers have suggested that overlaps between the UK’s current and replacement warheads might have necessitated lifting the cap, but the UK could have indicated this was a temporary measure if it had wanted to, and in any case it would not be required for some time. The same is true for any mismatch between production and dismantlement rates that could theoretically bring the UK over this cap. It is fair to say that a larger stockpile could ease the logistics burden and allow more warheads to be held at a high state of readiness if desired.

Factors relating to the practical delivery and maintenance of the current and future UK nuclear stockpile may well have had a significant bearing, though it is difficult to say how significant these factors might be – the government does not mention any issues in the review and clearly wants to keep the focus on the threat picture as the only driver. Key among these programmatic matters is the state of the UK’s nuclear infrastructure and the status of the US W93 warhead programme. In the case of infrastructure, if the cap increase is to be meaningful, one must assume that the government considers it feasible to bring the stockpile to between 225 and 260 warheads and maintain it at that level – despite well-documented difficulties with the UK’s warhead assembly and disassembly infrastructure.

In the case of the W93, Secretary of State for Defence Ben Wallace’s lobbying of US Congressional committee members over approvals for the first stages of the W93 warhead gives a clear indication of the degree of UK dependence on that programme. There has been some media speculation that the stockpile increase is a US-focused statement of intent, to add greater weight to arguments that the UK is serious about its replacement warhead programme. This would not, however, change the fundamental question for US lawmakers of whether the US needs the W93 as much or as quickly as the UK needs a replacement for its own weapons. This leaves open the question of whether the UK might need to make some tangible concession that encourages Washington to act as London would like it to, much as it did to facilitate the sale of Trident D5 missiles to the UK in the 1980s.

Deterrence Requirements

More warheads does not automatically mean more deterrence, though it may increase the number of targets that a single deployed submarine can hold at risk, or increase the likelihood that a credible two-boat patrol at a time of crisis could be achieved. This means that the number of operational missiles and deployed warheads that the UK might deploy at any one time has increased, perhaps quite substantially: both the Vanguard-class and Dreadnought-class submarine can carry vastly in excess of the 40 warhead limit that the review has dispensed with.

Although the UK has ceased to publicly discuss a ‘sub-strategic’ role for its nuclear arsenal, this increased stockpile and greater flexibility could provide greater room for the use of low-yield variants of its nuclear warhead to be threatened in a conflict. Given the emphasis that the review places on adversary states’ aggressive doctrines, it is certainly possible – and equally troubling – that this consideration has come into play for the UK.

In terms of strategic deterrence, the principal UK criterion for judging effectiveness in the past has been its own ability to inflict unacceptable damage on an adversary – historically, Russia, and particularly Moscow – rather than the number or type of nuclear forces possessed by that adversary. The UK has for several years mentioned countries other than Russia as potential nuclear deterrence counterparts; the review seems to imply that these threats are significant enough to warrant a larger deployed arsenal to credibly hold all of the targets that it needs to at risk. Similarly, the potential for future ballistic missile defences to become more effective, or for nuclear deterrent effectiveness to be degraded in some other way, has clearly been a source of concern for the government, which this policy shift might aim to address.

The final piece of the puzzle is the UK’s credibility and resolve from a potential adversary’s perspective. This uplift in arsenal is intended to signal that resolve to adversaries and allies alike, and it may have some effect in that regard. However, it will also be set against more tangible measures of the UK’s commitment to defence in general – such as its procurement and use of conventional military capabilities, its actions in the cyber and space domains, and its resolve and activism on diplomatic issues in general. Here the proof will be in the UK’s actions, but an increase in the UK’s nuclear deterrent capabilities alongside a reduction elsewhere would be a mixed signal.

Deterrence Requirementsarms Control and Disarmament

Since the UK’s first Strategic Defence Review in 1998, successive governments have made much of the UK’s post-Cold War nuclear reductions, both at home and in international diplomatic forums, especially relating to the Nuclear Non-Proliferation Treaty. The UK has also, since the mid-2000s, positioned itself as a leader in research on verification of nuclear disarmament, and has worked with non-nuclear-weapon states such as Norway to lay the technological groundwork for future arms control agreements. The review asserts the UK’s commitment to nuclear disarmament but offers no new steps to offset the impact of its stockpile increase and sets out no vision for future arms control negotiations in which the UK might be a player.

A move to a cap of 260 warheads winds the clock back to the 1990s, in that it reverses the UK’s course of progressively lower targets for reductions and greater transparency around operational deployments. In terms of international disarmament diplomacy, the decision is unequivocally damaging to the UK’s reputation. It will incur strong criticism at the upcoming Nuclear Non-Proliferation Treaty review conference. It risks making the UK’s arms control verification research and its partnerships with non-nuclear-weapons states look like a fig leaf, a theoretical exploration of a future scenario towards which the UK has no intention of seriously working. It could make it more difficult for the UK government to generate international condemnation of China’s nuclear build-up and China’s lack of nuclear transparency. And it will make life harder for UK partners that have been trying to persuade other non-nuclear states to keep the faith in a gradual, step-by-step approach to nuclear disarmament, in the face of the new Treaty on the Prohibition of Nuclear Weapons, which seeks to delegitimise nuclear weapons and ultimately make their possession illegal under international law. These costs stand in stark contrast to the emphasis placed elsewhere in the review on the importance of multilateralism and of the UK’s international partnerships and alliances.

Need for Scrutiny

The Integrated Review arrives at a moment of considerable change and disruption in the UK’s nuclear warhead programme. The last year has seen the announcement of a decision to build a new warhead, revelations about the UK’s nuclear dependence on the US, and the renationalisation of the Atomic Weapons Establishment. These developments, set against the background of the coronavirus pandemic and Brexit negotiations, have passed with little parliamentary comment. MPs, whether they support or oppose nuclear deterrence, should take today’s developments as their cue to get serious about scrutinising the UK’s nuclear warhead programme, as a matter of sound policy and expenditure if nothing else. A failure to do so would send a clear signal to the government that it can roll back existing levels of transparency and reporting around the nuclear programme without political costs.

The views expressed in this Commentary are the authors', and do not represent those of RUSI or any other institution.


Tom Plant

Senior Associate Fellow

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Dr Matthew Harries

Former Director of Proliferation and Nuclear Policy

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