| Introduction

On July 10, 2025, the joint declaration issued by British Prime Minister Keir Starmer and French President Emmanuel Macron at the Northwood military headquarters in northwest London marked a significant development in Europe's traditional discourse on nuclear deterrence. While reaffirming that each country's nuclear deterrent would remain independently maintained, the two leaders specified that their governments would pursue closer policy coordination and strategic consultation in response to the evolving European security environment.¹⁾ Specifically, the United Kingdom and France agreed to establish a Nuclear Steering Group (NSG) to coordinate their nuclear policies, thereby institutionalizing bilateral consultations on nuclear strategy, deterrence policy, capability development, and strategic messaging.

Building on the Northwood Declaration, the first NSG meeting was held in Paris in December 2025, during which a British delegation observed Poker, the quarterly nuclear deterrence exercise conducted by France's Strategic Air Forces, for the first time.²⁾ Although an Italian air-to-air refueling aircraft had partially participated in this exercise in 2022, this marked the first time France had opened the exercise to foreign officials. In March 2026, France unveiled its doctrine of forward deterrence (dissuasion avancée). While continuing to expand its nuclear warhead stockpile on the basis of the strict sufficiency principle, France announced that it would no longer disclose the size of that stockpile. Although control over its nuclear weapons would remain solely with France, without financial support from other states, Paris indicated the possibility of temporarily deploying strategic assets outside French territory. At the same time, France disclosed that it was engaged in nuclear-related discussions with eight European countries: the United Kingdom, Germany, Poland, the Netherlands, Belgium, Greece, Sweden, and Denmark.³⁾

In March 2026, German Chancellor Friedrich Merz, in a joint statement with President Macron, announced that France and Germany had established an NSG to discuss nuclear deterrence issues, encompassing the participation of German conventional forces in French nuclear exercises, joint visits by officials from both countries to strategic facilities, and the joint development of non-nuclear forces and capabilities with France and other European partners.⁴⁾ Subsequently, in July 2026, Chancellor Merz specified that German conventional forces would participate in French nuclear exercises before the end of 2026.⁵⁾ Polish Prime Minister Donald Tusk likewise stated that Poland was in consultations with France and its closest European allies on an "advanced nuclear deterrence program."⁶⁾

The external drivers of this shift are the growing Russian nuclear threat and the erosion of confidence in U.S. extended deterrence. As Russia's nuclear threat undermined the foundations of European security, credible nuclear protection and extended deterrence became indispensable, and this changing external environment provided the impetus for Europe's shift.⁷⁾ Beyond its violation of Ukraine's borders, Russia has heightened European threat perceptions through the increasingly offensive posture of its nuclear strategy, intensified nuclear threats and exercises, the use of dual-capable weapons, and nuclear sharing arrangements with Belarus. Meanwhile, the credibility of extended deterrence has been eroded by the United States' strategic pivot toward the Indo-Pacific and the resulting decline in the sufficiency of extended deterrence amid trilateral nuclear competition with Russia and China, as well as by the coercive alliance politics of the second Trump administration. Finally, underlying all of these developments has been Europe's own enduring aspiration for strategic autonomy.

In sum, at the core of Europe's security debate lies nuclear deterrence, widely regarded as the supreme guarantee of security, and the long-running debate over European deterrence has once again been reignited.⁸⁾ Discussions of European deterrence have persisted over time, varying only in intensity across different periods, and the Northwood Declaration between the United Kingdom and France, along with the interpretations it has generated, should likewise be understood within this broader context.⁹⁾ Most security specialists agree that, given Europe's relatively limited nuclear capabilities, European deterrence cannot substitute for U.S. extended deterrence in the near term; rather, the prevailing view holds that the former complements the latter.¹⁰⁾ What remains underdeveloped, however, is a rigorous theoretical account of how such complementarity might actually be achieved, along with corresponding policy recommendations.

Accordingly, this paper examines the debate over European deterrence through the relatively new concept of multilayered extended deterrence, and specifically proposes two models: a supplement model and an overlapping model. Each model carries its own strengths and weaknesses, and this paper does not render any a priori judgment between them. Both models acknowledge that, in practical terms, the foundation of European deterrence continues to rest on U.S. deterrent capability, but they diverge in how they conceive of the mechanism by which the former reinforces the latter. This distinction is illustrated through an examination of the 2025 Northwood Declaration and its subsequent developments. Guarding against the tendency to interpret Europe's recent moves solely through the lens of prestige or self-reliance, this paper instead observes the European security community's efforts to identify pragmatic alternatives within the constraints of limited capability, and draws theoretical implications from that observation.

| The Significance and Limits of the Northwood Framework

Europe's nuclear deterrence discourse has long been dominated by a framework combining U.S. extended deterrence with the independent minimum deterrents of the United Kingdom and France, that is, "U.S. extended deterrence plus the separate minimum nuclear deterrents of the United Kingdom and France." The core elements constituting this European deterrence architecture were the U.S. collective defense commitment under NATO Article 5, the forward deployment of U.S. non-strategic nuclear weapons such as the B61-12 together with escalation control and flexible response enabled by the U.S. W76-2, nuclear sharing through NATO's Nuclear Planning Group (NPG) and the operation and training of dual-capable aircraft (DCA), and the separate minimum nuclear deterrents maintained independently by the United Kingdom and France.

Notably, one of the defining features of France's approach to nuclear deterrence since the Cold War has been the concept of dual deterrence. The underlying logic held that if Soviet leadership, in contemplating the use of nuclear weapons, had to reckon simultaneously with the possibility of nuclear retaliation not only from the United States but from France as well, the Soviet Union's strategic calculus would become considerably more complex, thereby strengthening deterrence overall. It could be argued that a partial experiment in multilayered deterrence, or multilayered extended deterrence, was already underway at this stage.¹¹⁾ Nevertheless, the extent to which the core interests of the United Kingdom, France, and the United States were actually linked remained unclear, and no substantive nuclear cooperation materialized at the level of European deterrence.

European nuclear deterrence discussions have now evolved into a considerably more complex equation: "U.S. extended deterrence plus the separate minimum nuclear deterrents of the United Kingdom and France, plus Anglo-French joint deterrence, plus limited extended deterrence extended by the United Kingdom and France to their European allies."¹²⁾ In other words, as U.S. extended deterrence has weakened, the European component of deterrence has begun to diversify and strengthen, and the joint Anglo-French deterrent together with the limited extended deterrence that the United Kingdom and France now offer to their European allies constitutes an open declaration of multilayered extended deterrence.

The first element of this expanding European deterrent is the institutionalization of nuclear cooperation between the United Kingdom and France, which might be termed a nuclear entente.¹³⁾ The Northwood Declaration directly carries forward the 1995 Chequers Declaration, in which the two countries stated that they could not envisage a situation in which the vital interests of one could be threatened without the vital interests of the other being equally threatened.¹⁴⁾ The two countries have also, since 1992, regularly shared mutual interests, threat perceptions, and strategy through the Joint Nuclear Commission, and they jointly conduct tests at France's Epure facility to ensure the reliability and safety of their respective nuclear warheads.¹⁵⁾ Nevertheless, the 1995 declaration never developed into cooperation substantive enough to be characterized as mutual extended deterrence. A telling illustration of this gap in information-sharing over operational areas came in February 2009, when the two countries' SSBNs collided in the Atlantic.

The Northwood Declaration, by contrast, seeks to give substance to Anglo-French nuclear cooperation. It remains difficult, at this early stage, to assess precisely what degree of coordination is being achieved across nuclear policy, capabilities, and operations, and given the sensitivity inherent in nuclear affairs, the extent of information-sharing is not readily assessable from publicly available sources. None of the indicators of deepening cooperation proposed by some specialists, such as reciprocal SSBN port calls, coordination of SSBN patrol areas, cooperation on nuclear modernization, or the sharing of nuclear targeting information, has yet been observed. As noted above, however, a British delegation did observe a French nuclear exercise for the first time. Should British forces in the future contribute assets such as escort fighters or aerial refueling aircraft to this exercise, it would constitute a positive indicator that Anglo-French nuclear cooperation is beginning to acquire real substance.

Especially notable is the fact that the combined nuclear arsenals of the United Kingdom and France, at more than 500 warheads, now rival China's current nuclear stockpile. China's ongoing nuclear buildup has already begun to exert a tangible effect on U.S. operational planning and deterrence posture. The organic combination of British and French nuclear forces is likewise bound to be perceived by Russia as a challenge to its own nuclear calculus.¹⁶⁾ In July 2025, then Russian Deputy Foreign Minister Sergey Ryabkov remarked that, now that such cooperation had been formalized and placed on a stable and solid foundation, Russia would factor it into its military planning and not merely regard it as a political matter.¹⁷⁾ This suggests that Russia is closely monitoring Anglo-French nuclear cooperation and has little choice but to weigh the two countries strategically as a single, combined consideration.

The second element of the expanding European deterrent is the joint extension of British and French nuclear deterrence activities, that is, the provision of extended deterrence by the United Kingdom and France to Europe as a whole. In the Northwood Declaration, France and the United Kingdom included language stating that they agreed that no extreme threat to Europe could occur without eliciting a response from both countries.¹⁸⁾

France, in fact, has long invoked concepts such as concerted deterrence to reinforce the legitimacy of its nuclear status and to expand its nuclear role within Europe. President Macron himself proposed a strategic dialogue on French extended deterrence for Europe in both 2020 and 2025.¹⁹⁾ Macron's 2026 concept of forward deterrence, articulated within the context of NATO's nuclear mission, was intended to complicate adversaries' strategic calculations and add strategic depth through the dispersal of Rafale bombers.²⁰⁾ For its part, the United Kingdom reinforced the European dimension of nuclear deterrence in this declaration by explicitly stating that its nuclear forces exist to respond to extreme threats to Europe. To date, no concrete manifestations have been observed of protecting European allies' conventional forces, training to track Russian anti-submarine warfare assets, or building a European nuclear command-and-control architecture, at least not prior to the point at which British and French SSBNs would enter deep water. Nevertheless, France's forward deterrence doctrine is steadily taking shape, and discussions of nuclear cooperation are clearly gaining momentum across Europe, as evidenced by Germany's announced plans to participate in this exercise with conventional forces going forward.

The Northwood framework is not without its limitations, however. First, there is a longstanding line of criticism holding that the Northwood Declaration, much like the 1995 Chequers Declaration before it, amounts to little more than a political statement whose actual effect on deterrence on the European continent will prove minimal. In 1995 as well, the United Kingdom and France declared that they would strengthen their mutual deterrent and that this cooperation would contribute to deterrence across Europe as a whole, yet over the following thirty years, substantive change or contribution proved negligible. Concerns persist that the present declaration, too, may amount to nothing more than a political statement unaccompanied by strategic action. Doubts remain, in particular, as to whether French leaders who succeed Macron will carry forward the spirit of Northwood, given that France's staunch advocates of strategic autonomy can be expected to resist any move toward integration with a U.S.-led nuclear command structure.

Second, the expansion of the British and French nuclear role may fail to satisfy either of the two opposing constituencies within Europe, namely those with a "nuclear allergy" and the nuclear enthusiasts. From a nonproliferation standpoint, France's expanding warhead stockpile, its decision to stop disclosing the size of that stockpile, and the possibility that it may develop new tactical nuclear warheads are all developments that nuclear arms control advocates can hardly welcome, just as they remain wary of Russia's response through its own nuclear modernization. Nuclear-averse constituencies, for their part, can be expected to strongly oppose the entry of French or British nuclear-armed aircraft into their own territory. Nuclear enthusiasts, meanwhile, are likely to continue harboring doubts about the will and capability behind extended deterrence, given that the very origins of France's force de frappe lay in a fundamental distrust of U.S. extended deterrence. Neither the United Kingdom nor France possesses non-strategic nuclear weapons of its own, and the non-strategic nuclear weapons deployed on British soil remain U.S. assets tied to NATO missions. The strategic ambiguity that continues to characterize French nuclear strategy likewise falls short of providing European nuclear enthusiasts with sufficient reassurance.

Third, critics have argued that, should the additional deterrent capabilities now being pursued by the United Kingdom and France actually materialize, the result could be a further destabilization of the strategic environment. Such strategic instability could stem from uncoordinated deterrence operational planning and execution, potentially triggering unintended escalation and drawing in extraregional nuclear powers.²¹⁾ The European NSG, now being established in parallel with NATO's Nuclear Planning Group (NPG), risks either interfering with the latter's operational planning and execution or diverting forces away from those earmarked for NATO's deterrence missions. The fact that joint Anglo-French extended deterrence toward Europe is currently being tested alongside each country's own separate extended deterrence commitments only compounds concerns over an uncoordinated deterrence architecture.²²⁾ Russia, for its part, can be expected to respond to the expanding British and French nuclear role by further strengthening its own offensive nuclear posture, undermining stability in the broader arms competition. Finally, such European self-help measures risk signaling alliance fragmentation, a perception that could paradoxically lead adversaries to doubt the credibility of U.S. extended deterrence rather than reinforce it.²³⁾

Fourth, as many observers have pointed out, the capacity of the United Kingdom and France to provide extended deterrence for Europe remains inherently limited. Most of their strategic nuclear forces are delivered by SLBMs and are aimed at Russian countervalue targets, making them ill-suited as conventional instruments of extended deterrence. France possesses roughly fifty ASMP-A (Air-Sol Moyenne Portée, Amélioré) nuclear cruise missiles, strategic weapons with yields of 100 to 300 kilotons. Even granting the possibility of a lower-yield detonation below 10 kilotons for tactical purposes if required, such capability would pose little credible threat to a Russia that fields between 1,000 and 2,000 tactical nuclear weapons. In particular, France's continued reliance on strategic ambiguity as the basis of its nuclear strategy likewise fails to provide its allies with sufficient assurance. Beyond this, the extended deterrence capabilities of both countries remain constrained in other respects as well, including early warning, missile defense, and nuclear command and control.

| The Northwood Framework through the Lens of Multilayered Extended Deterrence

Despite the limitations enumerated above, Europe's ongoing experiment should not be dismissed simply as the product of self-reliant aspirations or as a provisional and unrealistic form of hedging. It represents a course of action that European states, having long relied on U.S. extended deterrence, might naturally explore and pursue amid a shifting international and nuclear order, and the process by which it is unfolding is highly pragmatic. This paper examines these efforts to strengthen European deterrence through the lens of multilayered extended deterrence. Indeed, some of the limitations identified above stem in part from the very nature of multilayered extended deterrence itself.

To begin, multilayered extended deterrence may be defined as the provision, by one state, of additional means and methods of deterrence to another state that is already receiving such deterrence from a separate provider. In the European context, multilayered extended deterrence takes the form of either supplementing the U.S. role, that is, partially replacing it, or overlapping with it. Under the first, supplement model, European states would assume responsibility for the middle or lower rungs of the escalation ladder in the event of nuclear conflict, with nuclear cooperation between the United States and Europe taking on a sequential or complementary character. European states would, in effect, occupy the lower-intensity rungs of the escalation ladder where U.S. capability is comparatively thin, serving as a stopgap that supplements U.S. extended deterrence. Under the second model, the effectiveness of multilayered extended deterrence rests on a mechanism whereby the activation of one deterrence system triggers another, with the mere possibility of such triggering itself registering as a threat in the mind of a potential adversary. Under this model, the activation of European deterrence would simultaneously invoke the activation of U.S. extended deterrence, and conversely, the activation of U.S. extended deterrence would in turn draw in European deterrence. In other words, this model emphasizes the overlapping and simultaneous character of nuclear cooperation. For example, were French Rafale bombers armed with nuclear cruise missiles to deploy to an air base in a particular NATO member state during a European nuclear crisis, Russia would have little choice but to reckon with the overlapping activation of two extended deterrence systems at once, adding further complexity to its strategic calculations. Here, European deterrence functions as a catalytic instrument. Both models, it should be noted, operate in ways that remain tied back to the ultimate source of extended deterrence, namely U.S. nuclear deterrence, and the boundary between the two models is not always sharply drawn.

Each of these two models carries its own vulnerabilities. In the case of the supplement model, there is a real risk of generating unintended, and potentially perverse, incentives for both the potential adversary and the state providing extended deterrence. The model carries considerable potential to trigger, or to be misread as triggering, the risk of strategic decoupling. If, for example, European deterrence comes to be perceived as activating first on the European battlefield, with U.S. extended deterrence following only afterward, this sequencing could further erode credibility unless it is carefully synchronized with NATO's nuclear command-and-control architecture, as it currently is. What Russia ultimately watches most closely is not the expansion of the British and French nuclear role as such, but rather what that expansion implies for the likelihood of U.S. involvement. In March 2025, a spokesperson for the Russian Foreign Ministry characterized France's forward-deployment doctrine as amounting to a substantial strengthening and expansion of NATO's nuclear forces.²⁴⁾ This suggests that, for the time being, Europe's multilayered deterrence efforts are being understood by at least this potential adversary as bound up with NATO, though this perception is by no means fixed and could shift.

The model that the United Kingdom is most likely pursuing is, in all probability, the supplement model. Britain has participated in NATO's nuclear planning since 1962, and its nuclear forces are already substantially subsumed within NATO's nuclear policy framework.²⁵⁾ A week before the Northwood Declaration, London announced the purchase of twelve F-35A DCA aircraft from the United States and signaled its intention to return to the NATO nuclear-sharing program it had withdrawn from in 1998. This points to a British contribution to European deterrence that will be pursued from within the broader framework of NATO extended deterrence rather than outside it. The United Kingdom can be expected to seek to close, through European deterrence, whatever gap emerges in NATO extended deterrence as a result of eroding U.S. credibility, while working to tightly bind the Northwood framework to that of NATO and to draw France into this same structure. To minimize disruption to NATO operations, Britain is likely to oppose the independent development of European early warning, missile defense, or nuclear command-and-control systems, and will remain wary of any unilateral European action that could deepen decoupling from the United States or send the wrong signal to a potential adversary.

The overlapping model, by contrast, does not require the same degree of fine-grained operational coordination with NATO, but it carries the risk of inadvertently undermining U.S. efforts at escalation control. Given the real constraints on its extended deterrence capabilities, France is likely to pursue multilayered extended deterrence primarily in the form of strategic overlap. The concept of dispersing French Rafale bombers to pre-designated European states in tandem with NATO's nuclear mission during a European nuclear crisis is itself an expression of the overlapping model. France may come to regard itself as exposing even its own homeland to Russian nuclear threat on behalf of its European allies, and the Northwood framework as a signaling mechanism that binds the fates of the United Kingdom and NATO together. In an actual limited nuclear war, however, France's airborne nuclear forces would, as currently constituted, offer little practical effect beyond a warning shot delivered through preemptive nuclear use.

If anything, this could generate unintended escalation that runs counter to NATO's own planning. Immediately following France's announcement of its forward deterrence doctrine in March 2026, a spokesperson for the Russian Foreign Ministry warned that the French measure would prove profoundly destabilizing. In April 2026, Russian Deputy Foreign Minister Alexander Grushko went further, suggesting that any European state agreeing to host France's nuclear-capable strategic bombers could itself become a target of Russian attack.²⁶⁾ This Russian response points to the possibility that Europe's own strategic instability could deepen as a result.

| Theoretical and Policy Implications

Europe's ongoing experiment with multilayered extended deterrence carries significant theoretical implications for South Korea. The South Korean government and its broader security community should closely track how this experiment continues to unfold and undertake careful study of both its possibilities and its limits. In particular, close observation and analysis will be required of the specific contours of future Anglo-French nuclear coordination, the extent to which the France-led NSG proves compatible with NATO's NPG, the trajectory of British and French nuclear modernization programs, and any resulting shifts in the nuclear strategies of both countries. Because the ultimate success of this experiment hinges on the attitudes of the United States and Russia, the reactions of Washington and Moscow likewise warrant continued attention. To date, the Trump administration's stance has ranged from positive to passive, while Moscow's response has been consistently negative. What is clear, in any case, is that Europe has raised a strategic question that neither the providers nor the recipients of extended deterrence can easily dismiss or ignore.

South Korea has, until now, relied entirely on U.S. extended deterrence to counter the North Korean nuclear threat, and amid today's shifting strategic environment, it is now exploring ways to expand its own strategic autonomy and build alternative security cooperation frameworks. Within the Indo-Pacific, however, there exists no middle power nuclear state positioned to provide South Korea with multilayered extended deterrence of the kind Europe is now experimenting with. Seeking additional extended deterrence commitments from the United Kingdom or France would amount to an excessive geographic overreach, and neither country would have much incentive to take on such a role. That said, the United Kingdom has recently, through the lens of "strategic stability," expanded its engagement with Indo-Pacific and Korean Peninsula issues, with the Foreign, Commonwealth and Development Office (FCDO) at the center of efforts to explore a role that could help fill gaps left by the United States. In France as well, nuclear security researchers at institutions such as the Institut français des relations internationales (IFRI) have been expanding contact with Korean security specialists. While such security cooperation is not aimed at providing multilayered extended deterrence as such, it could nonetheless serve as a foundation for more advanced deterrence cooperation down the road, and as a useful channel for information exchange in the meantime.

It is also worth examining whether the Conventional-Nuclear Integration currently being pursued by South Korea and the United States is oriented toward a supplement model or an overlapping model. Most current discussion points toward the supplement model, but it is worth also considering the possibility of an overlapping orientation, in which South Korea's use of conventional strategic weapons would serve to reinforce, rather than substitute for, the effect of U.S. involvement. At the same time, the ROK-U.S. alliance should place greater emphasis on strategic alignment rather than on strategic autonomy. What North Korea and South Korea's other potential adversaries will ultimately attend to is not South Korea's own independent deterrent capability, but the credibility of U.S. extended deterrence itself. South Korea should take care to ensure that its growing self-reliant capabilities are not perceived, by either the provider or the target of extended deterrence, as a sign of decoupling from the United States, and should instead work to achieve precisely the opposite effect. Finally, the expansion of South Korea's security horizons should be designed not to exclude the United States but to draw it further in. Whether in trilateral ROK-U.S.-Japan security cooperation, middle-power solidarity, or Global South strategy, these initiatives should be designed in ways that more firmly bind U.S. will and capability to the region, rather than loosen them.

1. GOV.UK, "Statement by the United Kingdom and the French Republic on Nuclear Policy and Cooperation," July 10, 2025, https://www.gov.uk/government/news/northwood-declaration-10-july-2025-uk-france-joint-nuclear-statement (accessed June 18, 2026).
2. République Française, "New UK-France Nuclear Steering Group Meets in Paris," December 22, 2025, https://uk.diplomatie.gouv.fr/en/new-uk-france-nuclear-steering-group-meets-paris (accessed July 18, 2026).
3. Michel Rose, "France to Boost Nuclear Arsenal, Involve European Allies in Deterrence," Reuters, https://www.reuters.com/world/europe/macron-says-france-will-increase-size-its-nuclear-arsenal-2026-03-02/ (accessed July 18, 2026).
4. République Française, "Strengthening Franco-German Cooperation in the Field of Deterrence," March 3, 2026, https://uk.diplomatie.gouv.fr/en/strengthening-franco-german-cooperation-field-deterrence (accessed July 18, 2026).
5. Daniel Niemann and Claudia Ciobanu, "Germany and France Initiate Nuclear Cooperation As Europe Seeks Greater Security Independence," AP, July 18, 2026, https://apnews.com/article/germany-france-nato-nuclear-exercise-macron-merz-2d03bccc2cc3519902597fa3691dc475 (accessed July 18, 2026).
6. Rose, 2026.
7. For example, France's 2025 National Strategic Review identified Russia as "the most direct threat, both now and for years to come, to the interests of France and its partners and allies, and to the stability of the European continent and the Euro-Atlantic region." The French Republic, National Strategic Review 2025 (July 2025) https://www.sgdsn.gouv.fr/files/files/Publications/20250713_NP_SGDSN_RNS2025_EN_0.pdf (accessed July 2, 2026); NATO has likewise stated that Russia's 2022 invasion of Ukraine poses the most serious threat to Euro-Atlantic security in decades. NATO, "Deterrence and Defence," June 25, 2026, https://www.nato.int/en/what-we-do/deterrence-and-defence/deterrence-and-defence (accessed July 18, 2026).
8. Bruno Tertrais, "Red Herring & Black Swan: A Bomb for Europe?" Berlin Policy Journal (October 30, 2018), https://berlinpolicyjournal.com/red-herring-black-swan-a-bomb-for-europe (accessed July 19, 2026); Barbara Kunz and Ulrich Kühn, "German Musings About a Franco-German or German Bomb," in Ulrich Kühn (ed.), Germany and Nuclear Weapons in the 21st Century (Routledge, 2024), 112-35; Michal Onderco and Ulrich Kühn, "Organizing Nuclear Policies in Europe: Of Bricoleur Plurality, Architect Absence, and Spoiler Disruption," International Politics 62 (2025): 947-58.
9. Commentary on the Northwood Declaration has already appeared widely elsewhere. Léonie Allard, "Reading Between the Lines of the New France-UK Nuclear Entente," Atlantic Council, July 16, 2025, https://www.atlanticcouncil.org/blogs/new-atlanticist/reading-between-the-lines-of-the-new-france-uk-nuclear-entente/ (accessed July 18, 2026); The International Institute for Strategic Studies, "The Northwood Declaration: UK-France Nuclear Cooperation and a New European Strategic Backstop," Strategic Comments (August 2025); Timothée Albessard, "The Franco-British Northwood Declaration: A New Model of Nuclear Partnership and Deterrence?" The Japan Institute of International Affairs, July 24, 2025, https://www.jiia.or.jp/eng/report/2025/07/column/2025/07/security-fy2025-01.html (accessed July 2, 2026); Bruno Tertrais, "Le parachute de secours: contours d'une dissuasion franco-britannique," (Summer 2025), https://politiqueinternationale.com/revue/revue-n-188/article/le-parachute-de-secours-contours-dune-dissuasion-franco-britannique (accessed July 2, 2026).
10. Tertrais, 2025.
11. Lawrence Freedman, The Evolution of Nuclear Strategy (New York: Palgrave Macmillan, 2003), 271-314.
12. This complex configuration is also reflected in the range of discourses and policy options unfolding within the United Kingdom and France themselves. See Bee Yun Jo, "Between Alliance and Autonomy, Again: The Limits of Europe's Strategic Autonomy Debate under Trump 2.0," National Strategy Vol. 31 No. 3 (2025): 37-66.
13. Allard, 2025.
14. République Française, "Déclaration conjointe franco britannique sur la coopération nucléaire entre les deux pays, Londres le 30 octobre 1995," 30 octobre 1995, https://www.vie-publique.fr/discours/132220-declaration-conjointe-franco-britannique-sur-la-cooperation-nucleaire-en (accessed July 18, 2026).
15. "The French/UK Joint Facility EPURE," n.d., https://www-teutates.cea.fr/uk/joint-facility-epure.html (accessed July 18, 2026).
16. The International Institute for Strategic Studies, 2025.
17. TASS, "Russia to Consider UK-France Nuclear Partnership in Military Planning: Senior Diplomat," July 11, 2025, https://tass.com/politics/1988021 (accessed July 2, 2026).
18. GOV.UK, 2025.
19. Élysée, "Address to the French People," March 5, 2025, https://www.elysee.fr/en/emmanuel-macron/2025/03/05/address-to-the-french-people (accessed July 18, 2026).
20. Wannes Verstraete, "Dissuasion Avancée: Macron's Realistic Complement to NATO Nuclear Deterrence," Egmont Policy Brief 403 (March 2026).
21. Pranay Vaddi and Vipin Narang, "Why We Extend Deterrence," Strategic Simplicity (blog), March 2, 2025, https://strategicsimplicity.substack.com/p/why-we-extend-deterrence (accessed July 18, 2026).
22. Examples include the Poland-France Nancy Treaty of May 2025, the UK-Germany Kensington Treaty of July 2025, and the joint conclusions of the France-Germany Defense and Security Council of August 2025.
23. Framing the relationship between alliance assurance and extended deterrence in these terms is a relatively new undertaking, and one that calls for further empirical research.
24. Reuters, 2026.
25. The Government of the United Kingdom, "UK to Purchase F-35As and Join NATO Nuclear Mission As Government Steps Up National Security and Delivers Defence Dividend," June 24, 2025, https://www.gov.uk/government/news/uk-to-purchase-f-35as-and-join-nato-nuclear-mission-as-government-steps-up-national-security-and-delivers-defence-dividend (accessed July 2, 2026).
26. Mark Trevelyan, "Russia Warns European States Against Hosting French Nuclear Bomber Planes," Reuters, April 24, 2026, https://www.reuters.com/business/aerospace-defense/russia-warns-european-states-against-hosting-french-nuclear-bomber-planes-2026-04-23 (accessed July 18, 2026).

※ The opinions expressed in 'Sejong Focus' are those of the author and do not represent the official views of Sejong Institute.