For deterrence to work, not only capabilities but also the credibility of the deterrent matters. Today, uncertainty over U.S. commitment to Europe threatens the continent’s security in ways it has not faced for decades. France and the United Kingdom are Europe’s only nuclear powers, yet their willingness to extend that protection to allies remains questionable. This article compares their doctrines with that of the United States to show where Europe’s nuclear safety net may fray.
Unsurprisingly, Donald Trump continues to dominate international headlines, sending regular waves of discomfort and uncertainty through U.S. alliances, particularly NATO. While some U.S. officials seek to reassure their allies, [1] [2] and many experts agree it would be unwise or even a strategic mistake for the U.S. to leave NATO, thus making it unlikely, [3] such arguments miss the point. Trump’s record shows him to be a transactional leader, driven by personal impulses and a taste for political drama. [4] [5] It would not be out of character for him to decide to leave NATO or, if not legally possible, at least reduce the real U.S. contribution while staying a member in name only. [6] Reports suggest that in 2018, he came close to doing exactly that, stopped only by the so-called “adults in the room” within the U.S. foreign policy establishment. [7] [8]
With likely no more “adult-in-the-room” figures in his circle, the threat is real, even though recent head-of-state meetings and the NATO summit went smoothly. Europe seems to have received that memo by now, with increased defense spending in nearly all countries to boost NATO’s conventional capabilities. [9] Despite some proposals, actual nuclear plans seem less advanced. [10] [11] Much of the discussion fixates on technology, budgets, and physical constraints when assessing alternatives to the American nuclear umbrella. This text instead addresses possible doctrinal and policy issues that could arise if the United States withdrew its nuclear guarantee would leave only the United Kingdom and France as NATO’s and Europe’s nuclear powers.
Nuclear Arsenals
Any assessment of nuclear doctrine must start with the hardware itself, since policy and capability shape each other. The UK, estimates suggest, has about 225 nuclear warheads. It is the only recognized nuclear weapon state relying on a single delivery system: the U.S.-supplied Trident II D5 submarine-launched ballistic missile (SLBM), with a range exceeding 10,000 km. The UK possesses around 48 of these missiles, deployable on four Vanguard-class nuclear-powered ballistic missile submarines (SSBNs), each with 16 missile launch tubes. [12] [13] Recently announced purchases of F-35s with a dual-capability license, giving them the option to carry U.S. nuclear gravity bombs, could hint at a planned aerial option in upcoming years. [14]
France operates four Le Triomphant-class SSBNs, each armed with up to 16 variants of M51 SLBMs, estimated to have a range of at least 6,000 km. Estimates suggest France has a maximum of 48 of said missiles. Unlike the UK, France has an air-delivered nuclear component. It fields roughly 20 ground-based Rafale B F3-R and 20 carrier-based Rafale M F3-R aircraft, all capable of delivering ASMPA nuclear cruise missiles (range ~500 km), about 50 of which are in the stockpile. France is estimated to possess just under 300 nuclear warheads. [12] [15]
As a true global superpower, the American nuclear arsenal far surpasses the arsenals of France and the UK in quantity and quality. The United States fields a complete nuclear triad, meaning air-, ground-, and sea-based launchers. Its total inventory consists of around 5,177 warheads of various kinds, some deployed, some in reserve, and some retired awaiting dismantlement. [16] Notably, around 200 of these are tactical B61 bombs, with 100 assigned to NATO allies and deliverable by dual-capable fighter jets. [17] [18]
Nuclear Basics
In all three countries, final authority rests with the civilian leader, either the president or the prime minister. [13] [19] [20] The United States stand out by publishing a detailed Nuclear Posture Review (NPR) every few years, now as a significant part of a National Defense Strategy. In contrast, the UK and France communicate their doctrine less formally, usually within varying defense or strategic documents. France also regularly conveys strategic positions through presidential speeches. Overall, American doctrine is presented in a more comprehensive and formal format, while the UK and France dedicate less space to it within their broader defense or foreign policy documents.
What Role Do Nuclear Weapons Play?
The outlined differences can be explained by the role nuclear weapons play in the three countries. As a global superpower, the United States field the largest arsenal, used for power projection and to provide extended deterrence to allies in Europe and Asia. [19] Therefore, a formal and comprehensive articulation can be expected. The political consensus on maintaining nuclear weapons is stable, [21] but their role in the deterrence framework, called integrated deterrence, is connected to conventional capabilities, particularly deterrence by denial efforts, such as missile defense. [22]
For the UK, nuclear weapons are a tool of sovereignty, but they usually refer to NATO when addressing their role. While described as operationally independent, the UK’s nuclear capabilities are technologically tied to the United States. They are seen as the ultimate deterrent within the broader framework, with less emphasis on deterrence by denial. [23] In historic tradition, nuclear weapons are also viewed as a factor ensuring Britain’s continued global reach, dating back to Churchill. [24] This theme continues: for example, the 2021 Johnson strategic document titled “Global Britain in a competitive age,” again puts increased emphasis on nuclear weapons, including an announced increase in the warhead cap and a new policy of not communicating specific capabilities. [25] However, before this shift and the invasion of Ukraine in 2022, nuclear weapons were viewed more controversially, and their necessity was questioned. A representative example is Labour’s former leader, Jeremy Corbyn, who publicly stated in 2015 that he would not use nuclear weapons and opposed replacing the system. [26]
In France, the role of nuclear weapons is even more profound. They are considered the ultimate deterrent, and other forms of deterrence are viewed with skepticism. Notably, nuclear capabilities are closely associated with national sovereignty and pride. As a result, France’s nuclear forces are operationally independent, domestically produced, and France does not participate in NATO’s Nuclear Planning Group (NPG). This pride and strategic independence explain why the role of nuclear weapons is rarely questioned in France. [27]
Approaches to Disarmament
Approaches to arms control and non-proliferation are very similar. The United States, UK, and France are members and reaffirm their commitment to the Non-Proliferation Treaty (NPT), supporting the finalization and entry into force of the Comprehensive Nuclear-Test-Ban Treaty and the Fissile Material Cutoff Treaty. At the same time, they all reject the Treaty on the Prohibition of Nuclear Weapons, viewing it as undermining existing agreements. [19] [28] [29] France holds the least optimistic view of disarmament prospects, [27] [30] while Britain has recently shifted to a more cautious stance. [23] The United States takes a slightly more positive approach in the Biden 2022 NPR, also compared to the Trump 2018 NPR. [19] [31]
How Could Nuclear Weapons Be Used?
All three rely on survivability and a robust second-strike capability. Still, the UK and France emphasize having a minimum credible deterrent, or a nuclear arsenal of strict sufficiency, as reflected in the low number of warheads and the emphasis on the purely defensive nature of their arsenals. This low-profile posture contributes to their relative skepticism toward disarmament. For both countries, the use of nuclear weapons is strategic by nature, and they rule out their use for tactical purposes. [27] Both maintain a continuous at-sea deterrent, meaning that at least one submarine is always on patrol to ensure a second-strike capability for strategic deterrence. [23] [27] Therefore, they do not possess tactical nuclear weapons, which constrains the options for laddered responses and escalation management. France maintains the unique right to use its strategic aerial component to issue a “final warning” before existential escalation, [30] but beyond that, the communicative role that nuclear weapons can play is limited for both nations.
The United States, on the other hand, with its nuclear triad and both strategic and tactical nuclear weapons, have the most flexibility. Its arsenal offers various options, such as limited strikes and precise nuclear signaling. Based on that, it has developed so-called tailored strategies for different scenarios and adversaries. [19]
When and Against Whom?
A rejection of a No First Use policy is a further commonality among the three, reserving them the right to use nuclear weapons even if not attacked with them first. Despite this, the United States and the UK offer negative security assurances (NSAs), stating they will not use or threaten the use of nuclear weapons against non-nuclear state NPT members in compliance with the treaty. Since 2021, the UK has left itself the option to review these NSAs if threatened with weapons of mass destruction or other threats with equal destructive potential. [25] [29] France used similar language, [32] but under President Macron, such assurances have vanished from the speeches and strategic documents. [30] [33] [34]
The United States and the UK state that nuclear weapons would be used only under “extreme circumstances,” while maintaining deliberate ambiguity about what exactly constitutes such circumstances. [19] [23] What appears regularly for France is the notion of “vital interests.” If these were threatened or under attack, a nuclear strike could follow, though no further explanation of these interests is ever provided. [30] [33] [35] This ambiguity is meant to complicate adversaries’ strategic calculations. But ultimately, despite more or less clear statements on the use of nuclear weapons, for all three countries, the final decision lies within the full authority of the presidents and the prime minister; therefore, depending on the person currently in office
Who Is Protected?
One of the most pressing questions today is how the three states view their arsenals in relation to their allies. All insist that ultimate control lies with them, but there are still differences. The United States uses very strong wording that clearly demonstrates its nuclear arsenal is part of extended deterrence. It frequently references its allies, particularly NATO, and places “the vital interests of the United States or its Allies and partners” on the same level, the ultimate gesture being NATO’s nuclear sharing. [19] The British position is equally clear, stating that their nuclear capabilities are “assigned to the defence of NATO,” establishing a consistent and well-defined link to its allies, specifically NATO members. [23]
France is far less clear in this regard. It was long absent from NATO’s military structure and never joined its NPG, although NATO states that France contributes to the alliance’s nuclear deterrent. [36] Interestingly, French documents and speeches usually refer not to NATO, but to the “Atlantic Alliance,” underlining the general sense of a less deep connection with NATO that persists in France. There is also a long history of French presidents linking France’s “vital interests” to Europe, though the intensity of this connection has varied over time. [35] Macron reinforced the idea in 2020, stating, “Let’s be clear: France’s vital interests now have a European dimension.” [30] While that logic is intuitive, a destroyed Europe around France would affect it too at its core, it’s unlikely that such statements will reassure France’s allies. Clearly, Ukraine is a geographically European country, so geography does not appear to be a decisive factor for Macron. Whether it is then an EU membership, or being a European NATO member, or simply having the Euro as the country’s currency, what touches the European dimension of France’s “vital interests,” remains open to debate. Additionally, while “vital interests” may include a European dimension today, such interests can evolve over time.
Conclusion
Doctrinal differences among the three states are not substantial, unsurprising given their shared alignment with the political West and ongoing nuclear cooperation, albeit more bilateral than trilateral. [37] Yet in a scenario where U.S. extended deterrence, long plagued by credibility doubts, is at its weakest, this overlap is a somewhat reassuring starting point.
Unlike the UK, which clearly states its nuclear capabilities serve NATO and its members, and thus all of threatened Europe, France’s ambiguity about the European scope of its “vital interests,” paired with its emphasis on national pride and independence, presents a challenge. While ambiguity can aid deterrence, it offers little reassurance to allies. France has yet to take part in formal nuclear planning or coordination, such as the NPG. Although France has offered to begin strategic talks, European partners have not embraced them, nor has France pressed the issue. [33]
This is not an insurmountable obstacle. Many proposals for Europe’s nuclear future have existed for years. Some are more plausible, such as a joint British-French deterrent, potentially funded by other European states, or separate arsenals with shared support. Others, like an EU deterrent with France ceding its weapons to the EU, remain far-fetched. [38]
Any such arrangement would require France to accept that its nationalistic stance and nuclear ambiguity cannot remain unchanged. If the United States were to fully withdraw, other European nations would be unlikely to accept the status quo. What now seems unlikely, nuclear proliferation by Poland or Germany, could gain momentum. If France wants to prevent this, as it expectedly would, it must send clear signals to its European partners. At a minimum, strategic talks should start now. Better still would be concrete steps that, while requiring commitment, are entirely feasible, like stationing dual-capable aircraft abroad, or pushing for a European Carrier Strike Group to support its carrier-based nuclear force. [39]
Even then, this would fall short of matching the credibility and commitment of U.S. nuclear sharing. The UK appears ready to expand its role in the nuclear domain. [14] [23] The question is whether France is prepared to do the same. Now is the time to show that there is more than just noise coming from Paris.
Article reviewed by Dávid Dinič and Veronika Zwiefelhofer Čáslavová
Cover picture: 2025 The Hague NATO summit. Source: Wikimedia Commons
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