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How could the UK augment its nuclear forces?

The use of nuclear weapons by an adversary is unfortunately no longer a distant fantasy but a real consideration for British defence and foreign policy officials. Russian nuclear rhetoric is becoming increasingly loose, and the People’s Republic of China (PRC) continues to expand and modernise its nuclear arsenal. The United Kingdom (UK) is also deepening relations with non-nuclear partners beyond the Euro-Atlantic area – such as Australia and Japan – to the extent that it may need to extend deterrence. In a very different era, how could the UK augment its nuclear forces? The recently announced Defence Nuclear Enterprise Command Paper goes some way in answering this; the Council on Geostrategy asked 11 experts in this week’s Big Ask to find out more.

David Blagden, University of Exeter

Augmentation of the UK’s nuclear arsenal could mean one of at least three things. There is a case for all of them, albeit with varying levels of urgency and downside cost.  

First, merely sustaining the current continuous at sea deterrent (CASD) posture is reportedly placing tremendous strain on the Navy. As such, UK nuclear forces need ‘augmenting’ just to preserve existing credibility. Resources are needed to recruit and retain the people necessary to keep the Vanguard class ballistic missile submarines (SSBNs) at sea, to ensure no further delays in bringing their Dreadnought class successors into service – already a decade later than planned – and to ensure protection of deployed/deploying SSBNs against advancing anti-submarine capabilities.

Augmenting UK nuclear posture may also entail reverting to an explicit doctrinal statement of Trident’s ‘sub-strategic’ potential. This was UK policy in the 1990s, but subsequently slipped out of official usage even as the W76/Holbrook warhead’s capacity for variable-yield and precision employment has reportedly increased. This may help to dissuade adversaries from counterforce nuclear strikes on UK/NATO targets in conditions where they estimated an Asia-focused United States (US) was distracted/disinterested while the UK/France were unlikely to escalate to a world-ending countervalue exchange. Similarly, UK nuclear command-and-control may benefit from augmentation via some variant of TACAMO capability – beyond the ‘Letter of Last Resort’ – to better ensure survivable deterrence while controlling escalation in a multipolar world of both nuclear and conventional precision-strike capabilities.

Most contentiously, new nuclear weapons and/or delivery systems might be added to Britain’s arsenal. For one, it may be worth hedging – via an easily regenerable latent-but-not-yet-fielded tactical weapons programme – against lessened US commitment, leaving NATO with an escalatory gap which a risk-acceptant adversary felt it could exploit for battlefield gain. Furthermore, as technological progress renders the oceans less ‘opaque’, it is time to start thinking about how the UK’s wholly SSBN-based nuclear force can be hardened and/or diversified to ensure its survivability as submarine-hunting advances.

Gabriel Elefteriu, Council on Geostrategy

Britain should restore air-delivered tactical nuclear strike capability. The UK is the only nuclear weapon state operating a single deterrent system (Trident). The last British tactical nuclear weapon, the WE 177 bomb, was withdrawn in 1998. Its planned replacement, the Tactical Air-to-Surface Missile (TASM), was cancelled in the aftermath of the Soviet Union’s collapse when sources from the Ministry of Defence declared that ‘to have proceeded with a second new nuclear system in the present international climate would have been “ridiculous”’. That logic has expired given Russia’s war against Ukraine and its behaviour towards NATO.

A return to the bad old days of an active Russian threat in Europe now warrants a resurrection of the nuclear calculations which we had in place before – and which kept us safe. The time has come for Britain to introduce an air-launched tactical nuclear missile. This would give the UK more flexibility on the escalation ladder and provide a versatile capability to attack heavy battlefield or naval targets in response to any similar Russian actions. By contrast, Trident, despite its ability to be configured for a sub-strategic role, is essentially a ‘last-ditch’ weapon reserved for – and one which would likely trigger – total nuclear exchanges.

The problem is money. One solution could be Germany, where the nuclear debate has revived as experts look for a back-up to the US deterrent which includes tactical nuclear options. At present the only remotely-viable course in this scenario would be to switch to a French umbrella, with Germany financing a larger force de frappe. But Britain also has a nuclear card to play, militarily and politically. The prospective new UK Labour government is already favourable to a defence pact with Berlin; this could include cooperation on an air-launched nuclear weapon, compatible with both British and future German F35 Lightning II combat aircraft, but Britain would of course need to acquire the ‘A’ variant first.

Euan Graham, Australian Strategic Policy Institute

From an Indo-Pacific perspective, a strategic need for the UK to factor deterrence of the PRC into its future nuclear posture is becoming increasingly clear. However, the key question is: can the UK achieve this solely through an expansion of its existing CASD, or will its patrol posture also need to change? 

If the Trident missiles have sufficient range, Britain could technically cover targets in the PRC from their current patrol areas in the North Atlantic. However, an obvious complication in the deterrence calculation is if these missiles then have to overfly Russia. A predictable Atlantic northerly orientation could also be easier for the PRC to counter through missile defence. There may be military utility in exploring Indian Ocean patrols for British SSBNs in order to complicate the defensive problem for the PRC, thereby helping to maintain effective deterrence into the long-term, as the PRC’s defensive as well as offensive capabilities grow in sophistication. 

There could also be value in reassuring a de facto UK ally, such as Australia, which currently relies exclusively on the US for extended deterrence. Indian Ocean deterrence patrols would also help underpin the strategic rationale for forward deploying a UK nuclear-powered attack submarine in Western Australia, to help safeguard the nuclear-armed boats among other tasks. Against this, however, it would also complicate the diplomacy of all three AUKUS countries if AUKUS begins to blur into the architecture of extended nuclear deterrence, potentially undermining Canberra’s emphasis on AUKUS as supplying a purely conventional form of deterrence. 

These are thorny problems which are likely to demand frank and open discussions among the UK, US and Australian governments in the classified realm. But that debate should also extend to a broader public conversation on the costs and benefits of the UK expanding its nuclear deterrent posture beyond the traditional focus area of the Euro-Atlantic.

Harry Halem, Yorktown Institute

The UK’s nuclear capability can be seen as a form of geopolitical ‘insurance’ in a volatile international environment. Yet as that environment deteriorates, with the Eurasian rimland descending into a period of military contestation, and the transatlantic relationship under stress, it is worth expanding and modifying the UK’s nuclear arsenal, with a particular focus on non-strategic nuclear weapons and an expanded CSAD.

The central objective of the UK’s strategy should remain the persistence of its ‘special relationship’ with the US, which allows British policymakers unrivalled access to decisionmaking in the world’s most consequential capital. This requires credible military forces and a coherent British strategy across Eurasia and globally – a reflex the British policy establishment lost from the late 1970s onwards. Nuclear weapons are an integral part of this strategic matrix, since they allow the UK to remain relevant at the apex of crisis, while also ensuring London retains some security independence in an existential confrontation.

Russian nuclear expansion and the odds of Russian aggression beyond Ukraine within the decade make a survivable UK second-strike capability crucial, as well as a more capable low-level arsenal. Furthermore, robust British nuclear capabilities will ensure London retains a direct line to Washington during European crises; the US will shift its strategic posture from Europe regardless of the results in November, but its interests in European stability will continue. 

The UK’s CASD is at the edge of its operational capacity. Measures to accelerate the procurement of the Dreadnought class SSBN would reduce fleet strain. Additionally, non-strategic weapons would provide British air and naval forces with the ability to influence the European balance independent of large-scale land-force deployments.

Beatrice Heuser, University of Glasgow

Since the 1960s, Britain has assigned its nuclear forces to NATO, ready to defend its continental allies with its nuclear weapons. Crucially, it might still be willing to do so even if an American president hesitates on committing to European security. This has been demonstrated in multiple NATO exercises and should increase deterrence, as having several decision-making centres means even if one is unwilling to cross the nuclear threshold, the other may.

So as not to be confronted with an all-or-nothing choice, one needs, at least, a second system for a last warning shot, in the hope that an enemy will back off realising they have miscalculated one’s determination to defend oneself. France has two systems but has never promised to defend its allies – French doctrine holds that extended deterrence is not credible. However, with only one system – submarine-based Trident missiles which when fired will give away the position of the submarine, even if that is from below the water – the UK is reduced to using it both for first use (the last warning shot) and to keep higher-yield forces to deter nuclear retaliation against Britain and/or its adversaries. 

The UK should acquire a second nuclear weapons system, comparable to the French Rafale aircraft with ASMP air-launched precision-guided missiles.

The British should not, for example, acquire a second system in the form of F35A Lightning II aircraft with American free-fall bombs which would be kept under American guardianship on British soil. First, the bombs themselves would remain under US control, so their use would still depend on US consent. Secondly, they are less precise than the ASMP missile, and they would require the aircraft transporting them to fly into enemy airspace to release them.

Tomas Jermalavicius, International Centre for Defence Studies, Estonia

The importance of NATO being a nuclear alliance and the UK as a nuclear power is not lost on the Baltic states. Estonia in particular draws comfort from the fact that all three nuclear powers of the alliance – France, the UK and the US – are militarily present on its soil. 

Nuclear deterrence provided by the UK, US and France is of major importance to frontline allies facing an existential threat posed by an aggressive Russia. Consequently, everything the UK (or France, or the US) does to ensure capability, credibility, and survivability of its nuclear forces should be viewed favourably in the Baltic capitals. Enhancing the available nuclear arsenal or expanding the range of means of delivery should be seen as sending a serious message to Moscow that its nuclear blackmail directed against the alliance is bound to backfire, and that decision-makers in London (or Paris, or Washington) also have an improved range of options available to them.

On the other hand, the Baltic states observe with some consternation how the UK’s conventional capabilities – especially in the land warfare domain – experience cuts which make them less credible in a protracted attrition war scenario where mass, reserves, and reconstitution capacity matter a lot. Every pound directed towards enhancing and sustaining the UK’s nuclear capability means a pound not spent on conventional warfighting and defence industrial capabilities. It is doubtful London can achieve a proper balance without increasing defence spending to 3% of GDP, or even more. In nuclear deterrence the Baltic states believe, but on conventional capabilities they rely, and that dampens their enthusiasm for more nuclear warheads if it comes at the expense of the UK’s ability to put boots on the ground and shells into artillery barrels.

Łukasz Kulesa, Polish Institute of International Affairs

It can be argued that the UK has already made the strategic decision to augment its nuclear forces, with the construction of the Dreadnought class SSBNs, development of a new nuclear warhead, and the large and recently announced investment in nuclear-related industrial capabilities which was designated a ‘national endeavour’. The 2021 Integrated Review included the decision to aim for an overall stockpile of ‘no more than 260 warheads’ in sharp contrast to previous plans to reduce the numbers.

At the same time, it is difficult to envisage a realistic scenario of expanding British nuclear forces further, especially by developing any additional sea-based or air-launched weapons and warheads. The political, financial and technological costs would be prohibitive – even if some argue that adding a ‘second leg’ to the British posture would be useful, e.g. for redundancy and signalling purposes.

Instead, the UK should look to maximise the deterrence effect of its existing nuclear capabilities. The credibility of the UK deterrent, declared to the defence of NATO, is important for Poland as well. The news about failed missile tests are not helpful in this regard, even when accepting that the latest test anomaly was ‘event specific’. Britain could signal more forcefully its ability to exert the power of its SSBN fleet in a crisis, for example by operating them in new maritime areas. Augmenting the UK’s role in NATO nuclear sharing should also be considered. This may include a deployment of American NATO-assigned nuclear bombs on British soil, or reviewing the role of UK forces in providing conventional support to NATO’s nuclear operations.

Jenny Mathers, Aberystwyth University

Vladimir Putin has made it a regular practice to threaten, either implicitly or explicitly, to use his country’s nuclear weapons if various red lines are crossed by the Euro-Atlantic democracies in their support for Ukraine – most recently, if NATO member states were to do as Emmanuel Macron, President of France, has suggested and fight alongside Ukrainian forces. 

Such threats cannot be entirely dismissed, but we should bear several things in mind when interpreting Putin’s nuclear sabre rattling. First, nuclear weapons have been a cornerstone of Putin’s public rhetoric since his very first term as president. He has used them to assert Russia’s position as a great power and to claim the attention, and the respect, of the international community, and especially that of the West. 

Second, many of the red lines identified by Moscow and defended with nuclear rhetoric (the delivery of Western artillery, air defence systems and tanks to Ukraine, as well as Finland and Sweden joining NATO) have been crossed without the use of Russian nuclear weapons. 

Third, the use of nuclear weapons is unlikely to bring Russia any advantages on the battlefield. Instead, the value of nuclear weapons for Putin lies in the threat of their use, rather than the execution. All of this suggests that Moscow’s threat to European security comes not from Russia’s nuclear weapons but from its conventional forces, which Putin has shown himself all-too willing to use. As a result, Western countries, including the UK, would be wise to focus their energies and resources on their own conventional capabilities rather than a new round of nuclear weapons production. 

Eoin McNamara, Finnish Institute of International Affairs

Yes, on pragmatic grounds. This answer might disappoint some arms control and disarmament advocates, but this is the sobering situation which Russian aggression has imposed on free and open countries. 

The PRC is also expanding its nuclear arsenal, with Beijing perceiving this as essential in its rise as a peer competitor of the US. The spectre of Donald Trump’s return to the US presidency in 2025 creates many difficult questions for security in Europe. 

Prior to Russia’s escalated aggression in Ukraine in 2022, a focus on conventional deterrence dominated defence debates in Finland and Sweden. Having now joined NATO, both states have added an emphasis on better understanding NATO’s extended nuclear deterrence posture. Events in Ukraine bring this extra layer of deterrence into sharp focus. While Finnish or Swedish conventional military strength could seriously damage Russia were it to encroach, the Russian army could commit many grievous atrocities in the process – just as it has done in Ukraine. 

The US is the main backstop for NATO’s extended nuclear deterrence, but if American leadership on this is paralysed by Trump, more responsibility will fall to the UK and France to uphold NATO’s full-spectrum of deterrence. It is therefore vital that Britain’s nuclear forces are strong and ready for this contingency. This is not a sign that global arms control and disarmament are permanently doomed, but that such initiatives are only realistic if nuclear powers agree to multilateral reductions. This looks a distant prospect  currently. 

James Rogers, Council on Geostrategy

In the Strategic Defence and Security Review of 2010, the nuclear payload of Britain’s CASD was reduced to just 8 Trident II D5 missiles equipped with only 40 warheads. Britain has taken Kenneth Waltz’s thinking on nuclear deterrence – ‘More is not better if less is enough’ – to extremis. To date, it has been right, for even if some missiles fail to launch or their warheads are shot down or fail to detonate, His Majesty’s (HM) Government still has the means to devastate any conceivable opponent.

This bare bones approach is probably sufficient to deter attacks on British territory well into the 21st century, but it is probably not enough should the UK decide to take on a greater burden in protecting its NATO allies, especially if the US becomes less willing or able to do so.

The current Vanguard class submarines were designed to carry 16 missiles, armed with 192 warheads between them. The new Dreadnought class SSBNs, which will replace the Vanguard class SSBNs from 2030, will be able to carry 12 missiles armed with eight warheads each (96 in total). If it has not already – the 2021 Integrated Review determined the UK would no longer specify its operational payload – HM Government should boost the number of warheads available and enhance readiness to fire.

In addition, to deter effectively attacks against its allies, the UK ought to ensure it can escalate using its conventional forces. The reinforcement mechanisms – i.e., response forces – between UK troops deployed in Estonia, Poland and elsewhere and the British powerbase should be augmented. Here, HM Government could boost the Joint Expeditionary Force by drawing in Poland to facilitate the speedy reinforcement of the Baltic states should Russia threaten to attack. By strengthening the connection between the ‘tripwire’ and the ‘trap’, Britain would bolster its ability to deter aggressors.

Peter Watkins*, King’s College London

The Defence Nuclear Enterprise Command Paper published earlier this week restated the familiar contours of the UK’s ‘independent, minimum, credible nuclear deterrent’: four submarines with Trident II D5 ballistic missiles delivering CASD. This construct – extant since the early 1990s and being renewed to endure until the 2060s – is informed by a strategic assessment whose key judgments go back to the late 1970s. While the Soviet Union has gone, the UK and NATO now face a weaker but more dangerous Russia as well as an increasingly powerful PRC (with a growing entente between the two).  

While HM Government is working to make the construct more resilient for a deteriorating geopolitical environment, how credible will it be to continue to rely on only one system to deter increasingly plausible contingencies such as threats of tactical or sub-strategic nuclear weapons use by an adversary? Responding with Trident could compromise our secure second-strike capability. We need to consider augmenting Trident with a separate sub-strategic capability such as we had until it was withdrawn – in a different world – in the late 1990s. One option would be to acquire the nuclear capable ‘A’ variant of the F35 Lightning II combat aircraft and fit it with a weapon carrying a new or modified warhead. This would be expensive – and put more pressure on an already stretched nuclear enterprise. But it would give future British governments additional credible options in a crisis – and so enhance the deterrence of nuclear threats to the UK and our allies.

*Author writes in a strictly personal capacity

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