U.K. Nuclear Weapons: Beyond the Numbers

8097399089_a202c5d19a_o (1) (1)

Sometimes numbers only tell part of the story, even when talking about nuclear weapons. For instance, the United Kingdom recently announced that it was increasing the cap on its nuclear stockpile from 225 to 260 warheads. The move — outlined in its government’s highly anticipated review of security and defense policy, Global Britain in a Competitive Age: The Integrated Review of Security, Defence, Development and Foreign Policy — largely took nuclear policy experts by surprise and reversed decades of British reductions. The government explained that the decision to increase its nuclear stockpile for the first time in decades was due to a worsening strategic landscape and technological threats, particularly Russian advances in missile defense and hypersonic weapons. The fact that the United Kingdom decided to make this decision now should be a wakeup call to those concerned about the security of the West and the global nuclear order.

The decision to boost the number of warheads in its arsenal wasn’t the only major nuclear policy change that the United Kingdom included in the Integrated Review. The document explained that the United Kingdom would no longer provide specifics about its nuclear stockpile or the conditions under which it would consider nuclear weapons use. In other words, the United Kingdom has now fully committed to a doctrine of strategic ambiguity. This approach is similar in some respects to what the United States, NATO, Russia, and China have done. But the increase in the warhead stockpile and reliance on strategic ambiguity come at a cost to nuclear diplomacy, and it will be difficult for the United Kingdom to balance these changes with its commitment to being a responsible nuclear power.

The announcement of an increase in the warhead stockpile, in particular, could not have come at a worse time for nuclear diplomacy. In August 2021, the United Kingdom and 190 other states will gather for a meeting of the parties to the Nuclear Non-Proliferation Treaty, which includes a commitment to the “cessation of the nuclear arms race” and “general and complete disarmament.” It will be a challenge for the United Kingdom to demonstrate progress towards nuclear disarmament five months after it has announced an increase in its stockpile cap. The reliance on strategic ambiguity also potentially undermines the country’s efforts to promote nuclear transparency among the treaty’s signatories. Obviously there are other considerations for the United Kingdom’s nuclear doctrine than the Nuclear Non-Proliferation Treaty, but these changes could damage its credibility on disarmament matters. The United Kingdom, therefore, should take additional steps to demonstrate its commitment to transparency, including providing more information on its nuclear modernization plans and leading on risk reduction efforts in the context of the Nuclear Non-Proliferation Treaty.

Reasons for a Larger Stockpile: Security and Technology

In its strategic reviews published in 2010 and 2015, the United Kingdom set a cap of 225 warheads and committed to reducing its stockpile ceiling to 180 warheads by the mid-2020s. The new Integrated Review increases the country’s nuclear stockpile ceiling to 260 warheads, a potential increase of approximately 15 percent from the current stockpile and 45 percent from the previous target.

The U.K. decision reverses decades of progress towards nuclear disarmament. Since the height of the Cold War in the 1980s, the United Kingdom has been gradually reducing its arsenal from a peak of approximately 500 warheads. At the same time, the United States and Russia have been reducing their arsenals through a series of bilateral arms control agreements. The United Kingdom’s decision to build more nuclear weapons places it in the company of China, India, Pakistan, and North Korea, which had previously been the only countries increasing their nuclear stockpiles. This decision by the United Kingdom, therefore, is a worrying reversal and suggests that the global nuclear order and nuclear stability might be in trouble.

The government justified the warhead increase on the grounds of “the evolving security environment, including the developing range of technological and doctrinal threats.” This bears many similarities to the 2018 U.S. National Defense Strategy, which highlighted complexity and competition in geopolitics. The link between nuclear policy and the overall security context echoes statements made by other nuclear possessors and NATO. For example, the 2019 NATO London Declaration stated, “We are fully committed to the preservation and strengthening of effective arms control, disarmament, and non-proliferation, taking into account the prevailing security environment.” (The Integrated Review uses identical language.) The United Kingdom’s role in NATO gets particular pride-of-place in the review — “We will continue to be the leading European Ally within NATO” — suggesting that while the United Kingdom might have left the European Union, it remains deeply committed to European security. The United Kingdom is also more concerned about China than in the past, and the review points to “China’s increasing international assertiveness and the growing importance of the Indo-Pacific.” The Integrated Review’s message coincides with U.K. concerns about China’s intervention in Hong Kong in breach of the handover agreement, along with a 2020 ban on buying Huawei’s 5G technology because it poses a “national security threat.”

The review cites “disruptive technologies” as a threat to strategic stability and as justification for increasing the warhead ceiling. In particular, it points to a “full spectrum of threats emanating from Russia.” Otherwise, it is vague about which capabilities are particularly concerning. Following its release, Secretary of State for Defence Ben Wallace explained that in order for the United Kingdom to maintain a credible deterrent, it had to respond to advances in Russian capabilities, particularly in missile defense. A week later, the government released Defence in a Competitive Age, a “defense command paper,” that pointed to hypersonic weapons and “early warning radar and integrated air defence systems” as potentially challenging U.K. military operations.

There are indeed plenty of causes for concern both in the security environment and with regard to technological developments. In particular, advances in Russian missile defense may be concerning to countries with smaller nuclear arsenals, such as the United Kingdom. The S-500, which Russia announced will be introduced later in 2021, is expected to be capable of intercepting ballistic, cruise, and, potentially, hypersonic missiles. (To be clear, the S-500’s full capabilities are unknown, and some experts have suggested that Russia’s anti-access area denial capabilities are “woefully overhyped.”) Other concerns include the breakdown of the Intermediate-range Nuclear Forces Treaty, and Russian advances in dual-capable shorter-range systems like the 9M729, which the United States alleged was in violation of the Intermediate-range Nuclear Forces Treaty. Many of these concerns resonate with a 2019 inquiry by the House of Lords, which concluded that nuclear risks were rising because of inter-state competition, technological developments, and nuclear doctrines and declaratory policy. These arguments, of course, will not persuade all experts, but the Integrated Review’s explanation is nonetheless plausible.

Doubling Down on Strategic Ambiguity

The United Kingdom is doubling down on its nuclear doctrine of strategic ambiguity. The government has never provided the exact size of its nuclear arsenal, and the recent review states, “we will extend this long-standing policy of deliberate ambiguity and no longer give public figures for our operational stockpile, deployed warhead or deployed missile numbers.” Previously, the country clarified the maximum number of warheads per submarine. The review also slightly changed the country’s declaratory policy to encompass a wider range of threats, stating that the United Kingdom will not use nuclear weapons against non-nuclear states party to and in full compliance with the Nuclear Non-Proliferation Treaty, but it reserves the right to review this in light of future threats from chemical or biological weapons, or emerging technologies. Like the warhead increase, this slight change in declaratory policy to include “emerging technologies” was justified on the grounds of a worsening security environment and technological advances by Russia and, to a lesser extent, China.

The goal of strategic ambiguity for the United Kingdom is to inspire caution in an adversary in a crisis and to deter nuclear use. Arguably, China and Russia have been practicing strategic ambiguity for years while also modernizing their nuclear arsenals. The United States and United Kingdom are catching up, with the aim to convince decision-makers in Moscow and Beijing that the risks of miscalculation are too high to pursue regional adventurism or aggression.

The British decision renewed an ongoing international debate as to whether strategic ambiguity is stabilizing or de-stabilizing, which was particularly evident at the time of the U.S. 2018 Nuclear Posture Review. Supporters of strategic ambiguity, including many U.S. allies (e.g., Australia), argue that strategic ambiguity deters Russia or China from using “conventional military force to impose their will, without having to worry about a nuclear riposte from the US, so long as they themselves remained below the nuclear threshold.” Complicating adversaries’ strategic calculus through doctrinal ambiguity, so the thinking goes, strengthens deterrence.

Conversely, opponents of strategic ambiguity fear that it increases the risks of misperception and misunderstanding, particularly during a crisis, and will “increase the risk of nuclear escalation and undermine global security.” And for others, such as MP Tobias Elwood, chair of the House of Commons Defence Select Committee, it is an insufficient response to growing threats, such as from China. For now, strategic ambiguity is an understandable response to geopolitical uncertainty, whereby the United Kingdom wants maximum flexibility to respond to as wide a range of threats as necessary.

The Price of Ambiguity

Alas, the increased nuclear stockpile and the doctrine of strategic ambiguity will undermine the United Kingdom’s nuclear diplomacy. The move will open the country up to charges of hypocrisy. Future British delegations to international nonproliferation and disarmament negotiations should expect to be asked why other countries should make progress on these issues when the United Kingdom is building up its own nuclear arsenal. While this may seem relatively inconsequential compared to deterring Russian nuclear forces, it will make it harder for the United Kingdom to advance its interests in other areas that it cares about, especially within the Nuclear Non-Proliferation Treaty.

The United Kingdom has historically demonstrated more restraint and transparency compared to the other officially recognized nuclear weapons states under the Nuclear Non-Proliferation Treaty (i.e., China, France, Russia, and the United States). Under a Labour government, Foreign Secretary Margaret Beckett indicated in 2007 that the United Kingdom could be a “disarmament laboratory,” and the country has indeed led research into disarmament verification, inspiring even larger efforts such as the International Partnership for Nuclear Disarmament Verification. Three years later, this time during a Conservative government, Foreign Secretary William Hague committed to a “more open policy” on Britain’s nuclear weapons and announced that the stockpile would not exceed 225 warheads. More recently, in 2019, the United Kingdom held a workshop to discuss its nuclear implementation report to the Nuclear Non-Proliferation Treaty, which included clarification of its nuclear doctrine and terminology. It was the only nuclear weapons state to take such a move, and as one of three non-governmental participants at the workshop, I can confirm it was a truly frank and open dialogue. The British delegation showed much more transparency than its counterparts.

With the United Kingdom’s decision to increase its nuclear stockpile and become more ambiguous on nuclear matters, much of that progress and credibility may be called into question. Additionally, this could reinforce narratives from supporters of the Treaty on the Prohibition of Nuclear Weapons, who are dissatisfied with the slowing pace of disarmament and pressuring the United Kingdom and other NATO members to join the treaty. Moreover, it will exacerbate concerns that nuclear possessors are moving in the wrong direction. This has been a particularly difficult and polarizing debate during recent meetings of the parties to the Nuclear Non-Proliferation Treaty. Some analysts have already argued that the stockpile increase is incompatible with the United Kingdom’s commitment to nuclear disarmament under the treaty, and it could also increase distrust within the “P5 process,” meetings of the five recognized nuclear weapon states to discuss opportunities for progress towards nuclear disarmament. The U.K. review will to some extent make it harder for President Joe Biden’s administration to tell a positive story about arms control and disarmament following the five-year extension of New START. It seems unlikely, therefore, that the United Kingdom would accept these potentially significant diplomatic costs, particularly in terms of its relationship with the new Biden Administration, if the strategic and security justifications were “all a ruse.”

U.K. Nuclear Policy After the Integrated Review

There are two relatively modest measures that the United Kingdom can pursue in an attempt to rebuild some of its credibility going into the Nuclear Non-Proliferation Treaty Review Conference — clarifying its nuclear modernization plans, and pursuing risk-reduction measures in the context of the P5 process. These are realistic steps that the country could take at relatively low cost that would preserve its security interests and give British diplomats some leverage in future disarmament and nonproliferation talks.

First, the government could provide more information about its nuclear modernization plans. In 2016, the House of Commons voted to maintain the United Kingdom’s nuclear deterrent, and the current Vanguard-class submarines will be replaced with the Dreadnought class, which will become available in the 2030s. The government is also planning to replace its current Trident warhead, the Holbrooke, which is similar to the American W76 warhead, with a replacement warhead that might not be available until the 2040s. If the United Kingdom does increase its stockpile in the meantime, these warheads will likely come from a stockpile that are not “operationally available,” such as those previously assigned for decommissioning or going through re-assembly and thus not counted towards the current overall stockpile.

But major questions remain about the future of the U.K. arsenal, with implications for the independence and credibility of the deterrent. The government states that the United Kingdom’s nuclear deterrent is “operationally independent”, but historically the United Kingdom has relied on cooperation with the United States for capabilities such as Trident missiles and warhead technology, such as the W76. Moreover, a new Common Missile Compartment is being developed in conjunction with the United States. Exceptional research by Tom Plant and Matthew Harries at the Royal United Services Institute has raised questions about this relationship between U.K. and U.S. nuclear programs and highlighted ongoing challenges with British nuclear infrastructure.

The status of the replacement warhead is particularly muddled, with one official saying it will be a “joint project, in design terms” with the United States, along with reports of Wallace lobbying Congress to fund the W93. The day before the Integrated Review was released, the government finally provided more information about the independence of the replacement warhead project:

We are working with our U.S. counterparts to ensure the UK replacement warhead remains compatible with the Trident missile. The UK Replacement Warhead will be designed, developed and manufactured in the UK. It will be housed in the Mk7 aeroshell, as will the U.S. W93 warhead, but the requirements, design and manufacture of the warheads are sovereign to each nation. This is consistent with our obligations under the Treaty on the Non-Proliferation of Nuclear Weapons.

This is an important first step in clarifying the relationship between the W93 and the replacement warhead. The release of the Integrated Review presents an opportunity for Parliament to ask additional questions about the replacement warhead, and for the government to answer them and try to rectify the muddled messaging to date. To start with: What are the requirements for the replacement warhead? And how much will it cost? To be clear, the government should not reveal sensitive information about warhead design, nor should it reveal stockpile numbers. Instead, it should provide assurances to Parliament that the U.K. deterrent is indeed independent and credible.

Second, the United Kingdom will need to focus on opportunities to reduce risks of misperception within a doctrine of strategic ambiguity. For example, the five nuclear-weapon states have been slow to restate that “a nuclear war cannot be won and must never be fought.” If they are unable to jointly agree to this language, the United Kingdom could make a unilateral statement to a similar effect or with the United States and France, another partner on nuclear weapons issues. Another option would be offering concrete proposals for crisis communication channels, or for mitigating the risks that new technologies and doctrines of ambiguity present to nuclear stability, either within the P5 process or in the Creating an Environment for Nuclear Disarmament working group. This might include a cyber “no-first use” agreement among the recognized nuclear weapon states, expanding the “cyber hotline,” or a proposal on limiting space-based threats. Ultimately, the United Kingdom should be seeking concrete and practical tools to ensure that strategic ambiguity does not lead to strategic misperception. Ideally, all nuclear possessors would pursue such tools, as Russia and China also practice strategic ambiguity but don’t seem to come under the same scrutiny or criticism for doing so.

A Nuclear Wakeup Call

As a response to the worsening global security environment and technological advances, such as those made by Russia and China, it makes sense for the United Kingdom — with a relatively small nuclear arsenal to begin with — to increase the size of its nuclear stockpile and rely more heavily on strategic ambiguity. Nonetheless, it comes at an unfortunate time for the international nuclear order and British nuclear diplomacy. The government will have to work across Whitehall to try to rebuild the United Kingdom’s credibility as a leader in transparency and disarmament going into the 2021 Nuclear Non-Proliferation Treaty Review Conference. This will not be an easy task.

Nothing can likely save the conference from the polarization that has defined it in recent years. The United Kingdom’s new stockpile ceiling will not be the thing that leads to failure at the upcoming gathering. But it certainly doesn’t help. What really matters here is that the United Kingdom, a leader in nuclear disarmament among the nuclear possessors, perceives the security environment to have become so much worse that it chose to increase its nuclear stockpile amidst growing pressure to disarm. It perceives the technological landscape to be increasingly dangerous, and would jeopardize its leadership on nuclear transparency in response. These are worrying trends indeed that should be a wakeup call to the changing nature of strategic threats. A change in the stockpile should say more about the security landscape than it does about U.K. nuclear warheads, but that remains a difficult story to sell.



Heather Williams, Ph.D., is a Stanton Nuclear Security Fellow at the Massachusetts Institute of Technology. She is visiting from King’s College London, where she is a lecturer in the Centre for Security Studies and Defence Studies Department. Her research focuses on arms control and emerging technology, the global nuclear order, and social media and nuclear escalation.

Image: U.K. Ministry of Defence (Photo by Stu Hill)