Revisiting Deterrence: Towards a French Nuclear Umbrella Over Europe?

CSDS POLICY BRIEF • 6/2025

By Elie Perot

20.3.2025

Key issues

• As the crisis of trust across the Atlantic deepens, European allies are now openly considering alternatives to the American nuclear umbrella, based notably on France’s deterrent.
• To enhance the protection offered by French nuclear deterrence to European allies, adjustments can be made over the short- and long-terms.
• The strengthening of the French nuclear umbrella over Europe should be part of a broader reinforcement of the continent’s “strategic deterrence” vis-à-vis Russia.

Introduction

After just two months in office, the second Trump administration has opened a major rift within the transatlantic relationship. The crisis of trust across the Atlantic has reached such levels that European political leaders are openly considering alternatives to the American nuclear umbrella, considered for the last 75 years as their ultimate security guarantee. Most notably, the likely next chancellor of Germany, the Christian-Democrat Friedrich Merz, argued last February that his country needed to ‘have discussions with both the British and the French – the two European nuclear powers – about whether nuclear sharing, or at least nuclear security from the UK and France, could also apply to [the Germans]’.

French president Emmanuel Macron responded to this “historic call”, as he termed it himself, in a televised address on 5 March, indicating his decision ‘to open the strategic debate on the protection by [France’s] deterrent of [its] allies on the European continent’. It is clear, however, that the French nuclear deterrent will not be shared, in a strict sense, with the rest of Europe. As Macron also stressed in his address, French nuclear deterrence is ‘complete, sovereign, French from start to finish’ and, ‘whatever happens, its decision has always been and will remain in the hands of the President of the Republic, commander-in-chief of the [French] armed forces’.

Given these conditions, this CSDS Policy Brief explores what steps could be envisaged to strengthen the protection offered by French nuclear forces to Europe.

In the short-term, the language of French doctrine could move more explicitly towards the logic of extended deterrence vis-à-vis European allies. Operationally, French airborne nuclear exercises could increasingly involve other European armed forces. Politically, France could also move closer to NATO on nuclear issues. In the long-term, should trust in the American umbrella fail to be re-established, more far-reaching changes could be made to French nuclear deterrence. One may envisage the possibility to host, temporarily or permanently, French airborne nuclear forces in other European countries. France’s escalation doctrine could also become more gradual, so as to gain credibility in the eyes of European allies. At any rate, the strengthening of the French nuclear umbrella over Europe would have to be part of a broader reinforcement of the continent’s “strategic deterrence” vis-à-vis Russia, involving not only the United Kingdom’s (UK) own nuclear forces but also additional high-end conventional contributions from other European nations.

In the short-term

Ever since the establishment of its force de frappe during the Cold War, France has considered that its nuclear deterrent played a protective role on a continental scale, beyond French national borders. This idea has been repeated, more or less forcefully, by successive French presidents, who have sole authority to determine the country’s nuclear doctrine. In recent times, the European role of the French nuclear forces was underlined in 2015 by former French President François Hollande under the form of a rhetorical question: ‘France has real, heartfelt solidarity with its European partners. So who could believe that an aggression threatening Europe’s survival would have no consequence?’. President Macron, for his part, positively affirmed in his 2020 speech at the Ecole de Guerre that ‘France’s vital interests now have a European dimension’.

All French presidents, including Macron, have been reluctant, however, to veer away from the traditional French conception of a nuclear doctrine circumscribed by the country’s “vital interests” (that is, in the French nuclear lexicon, interests that, if challenged, could warrant the use of nuclear weapons), even if these vital interests have been explicitly defined within a continental perspective. In the eyes of the French authorities, this is a question of credibility: the idea is that France can credibly threaten to use nuclear weapons only if its vital interests are at stake. But this somewhat inward-looking way for France to conceive of its nuclear doctrine has sometimes left its European partners – especially those who are not France’s direct geographical neighbours – uncertain about whether Paris would use nuclear weapons in their defence.

A doctrinal adjustment that France could consider in the short-term would be to move closer towards a logic of extended deterrence while preserving the credibility logic of the reference to “vital interests”. How to square this circle? One way to do so would be for the French President to state that France’s vital interests include ‘the protection of its European allies’ – to use the expression that Macron himself employed in his recent television address. Another possible way would consist in explicitly recognising that the vital interests of France and its European allies are intertwined. The model here would be the Franco-British Declaration of Chequers, adopted in 1995, which states that France and the UK ‘do not see situations arising in which the vital interests of either France or the United Kingdom could be threatened without the vital interests of the other also being threatened’ – a point reaffirmed in the 2010 Franco-British Lancaster House Treaty and the 2023 UK-France Joint Leaders’ Declaration. Of course, nothing would prevent the two different formulas just mentioned to be used in conjunction, or from being the object of a joint declaration rather than only a unilateral statement by the French president.

In his 2020 speech, President Macron also opened the possibility for European partners to ‘be associated with the exercises of French deterrence forces’, so as to create a common ‘strategic culture’ – an offer he recently reiterated in an interview with the French newspaper Le Figaro. It is difficult to assess to which extent Europeans have exactly responded to this offer. But in a parliamentary hearing in 2023, the chief of the French air and space force staff indicated that ‘as part of the Poker operations, [European partners] sometimes take part in simulated enemy operations, as was the case recently with an Italian refuelling tanker’ – “Poker” being the name of the regular training exercise of the airborne leg of the French nuclear forces, simulating a nuclear strike.

What additional steps could be taken in this regard? First of all, more European countries may now be interested in joining such exercises by the French Strategic Air Forces (FAS – Forces Aériennes Stratégiques), and France should still encourage them. In addition, France and its partners could also consider expanding the role that participating European forces may play in the Poker exercises, including in a combat role and as part of the “Blue team”. This would certainly raise for France delicate issues of confidentiality. But it is by playing a conventional role in support of French nuclear airborne operations – that is, by providing not only air-to-air refuelling or intelligence support, but also, potentially, by helping to suppress and destroy enemy air defences, thereby opening up corridors for a nuclear strike – that European conventional forces would be most useful, in operational terms, to a reinforcement of French nuclear deterrence. Finally, the geographical scope of Poker exercises could be expanded. To date, these exercises take place over French territory and adjacent seas. A political signal would be sent if European countries were ready to not only associate their forces to Poker exercises but also to welcome part of these exercises within their airspace.

Finally, from a political standpoint, it may be important for France to give some guarantees that, on the one hand, a reinforced European role for French nuclear forces would not be meant to undermine the transatlantic alliance – an ulterior motive that France is sometimes suspected to harbour – and that, on the other hand, Europeans would be consulted on how a French umbrella would be deployed over them. One way to achieve this would be for Paris to move closer to the information sharing and decision-making processes on everything nuclear within NATO, for instance by joining as an observer the NATO Nuclear Planning Group (NPG) and its subordinated bodies. Alternatively, one could also set up an ad hoc framework outside NATO that would serve, mutatis mutandis, the same purposes as the NPG among Europeans.

In the long-term

The measures mentioned above could relatively easily be implemented in the forthcoming months or years, in response to the growing uncertainties arising over the United States’ (US) umbrella under the second Trump presidency. More far-reaching adaptations of French nuclear forces could also be envisaged over the long-term though, especially if the transatlantic split were to be confirmed even after the end of the current US administration.

Yet, the relative inflexibility of France’s nuclear doctrine may not be entirely warranted by the structure of its nuclear arsenal. France has a total of 290 operational nuclear warheads. 240 of these are mounted on the M-51 submarine-launched ballistic missiles operated by France’s Strategic Oceanic Forces (FOST – Force Océanique Stratégique), while 50 nuclear warheads equip the ASMP-A cruise missiles of the French nuclear air force – 40 for the FAS and 10 for the Force Aéronavale Nucléaire (FANu – Nuclear Air Force), the airborne force that can be deployed, if required, from the Charles de Gaulle aircraft carrier. It is reasonable to suggest that tactical considerations imply a certain rigidity of use when it comes to the sea-based French nuclear capabilities, since the firing of just one of the 16 M-51s from the single Triomphant-class submarine that is normally on patrol would be detected by an enemy, who might then try to destroy that submarine to prevent further missile launches. Even then, though, the time elapsed between the detection of a missile launch and the possibility of actually intercepting the French submarine would give the latter some possibility of re-diluting at sea, within a radius increasing with each passing minute. Moreover, in the event of an acute international crisis, France would likely take the preventive step of sending another ballistic missile submarine on patrol, as was the case shortly after the start of Russia’s invasion of Ukraine in February 2022. As far as France’s air-based nuclear capabilities are concerned, however, there is little evidence to suggest that their use needs to be as inflexible as officially envisaged in French nuclear doctrine. In practice, what is to prevent the France’s arsenal of 50 nuclear-tipped cruise missiles from being used in different waves, each involving a limited number of nuclear strikes?

The strategic debate in France has often avoided directly addressing such considerations, perhaps because they tend to put into question the axiom of the “nuclear revolution” on which much of French nuclear thinking is based. Instead, the argument put forward in response has been that a French umbrella derives its credibility from the fact that France is geographically situated on the European continent and should therefore be more willing to protect the rest of Europe with its nuclear weapons. While this view certainly has some merits, such an essentially political argument may not be sufficiently convincing to European allies and potential adversaries, and it may thus still prove necessary for France to also consider changes to its doctrine and capabilities in order to provide further reassurance and deterrence.

In this perspective, France could eventually adopt a more gradual escalation doctrine, offering for more options between a last warning and a full-blown nuclear strike, thereby aligning itself more closely with what the French nuclear arsenal is arguably already capable of doing in practical terms. As regards capabilities, it would not be impossible, in time, for France to expand its airborne nuclear arsenal, notably by bringing into service a few dozens more ASN4G missiles than has been envisaged to date and, correlatively, by modestly increasing its total nuclear stockpile. In fact, such an expansion may already be in the pipeline. Earlier this week, President Macron announced that Luxeuil airbase in eastern France would be modernised to be able to host within a decade the “next two squadrons” of the FAS. Should these two nuclear squadrons come on top of the two that are already in service (a point that is not yet entirely confirmed at the moment of writing), this would mean the doubling of the size of the FAS and, therefore, possibly of the number of nuclear missiles these forces operate.

Conclusion: the broader European landscape

An important hurdle on the way towards a stronger European role for France’s nuclear forces – whichever form the latter may take – is that it would create an asymmetry between France and its European allies. Over the past 75 years, Europeans have accepted this asymmetry, if not always happily, vis-à-vis their US protector, who has the advantage of being both geographically distant and undeniably more powerful than any European country taken individually. France is, by contrast, a European country itself, and therefore geographically close, and does not stand head and shoulders above all its European partners (except in the case of its nuclear weapons). Moreover, the prevailing norm in relations between European countries is one of equality, thus ruling out the decisive, individual leadership of any one of them. In consequence, for it to be accepted, a stronger European role for French nuclear deterrence would need to strive to minimise as much as possible the asymmetry that it would necessarily create between France and its European allies.

A French nuclear umbrella over Europe should thus be conceived as part of broader sharing of responsibilities, risks and leadership to ensure the continent’s “strategic deterrence” vis-à-vis Russia. This implies, firstly, involving the UK as much as possible. A strengthened role for the French nuclear deterrent in protecting Europe should indeed be devised as part of a joint initiative with the British. This would not only offer a mechanism for increased cooperation and coordination between London and Paris but would also inspire greater confidence from the other Europeans, who would likely prefer not to have to deal with a single nuclear interlocutor on the continent. Secondly, other European nations could step up their efforts to acquire high-end capabilities with strategic effect – in particular long-range strike capabilities, such as conventionally-armed cruise missiles, or advanced air and missile defence systems, so as to create an integrated and multi-layered air defence over the continent, as foreseen for instance under the German-led European Sky Shield Initiative. This would ensure that the future defence of the continent against Russia would be a truly common European effort, with each nation contributing according to its own means and capabilities.

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