Can Europe Build Its Own Nuclear Umbrella?

Why the surge of interest in a European nuclear force?

The administration of U.S. President Donald Trump, after only a few weeks in office, has raised serious doubts among its European allies about America’s commitment to their security and the NATO alliance. Recent leaks confirm the antagonism leading members of the administration feel toward Europe. This has led Europeans to seriously worry about whether Washington will continue to extend nuclear deterrence—sometimes referred to as a nuclear “umbrella”—to the continent. Some leaders have begun to discuss their nuclear options.

Allied doubts about U.S. extended deterrence commitments are an inherent feature of the relationship, not just a Trump effect. In the 1950s, the belief that a U.S. president would never sacrifice “New York for Paris” became a justification for France’s pursuit of a nuclear weapons capability independent of the United States. What’s more, selective releases of intelligence throughout Russia’s full-scale invasion of Ukraine indicate that, despite its threats, Moscow has not yet taken any concrete actions to increase the risks of nuclear war. It has not, for instance, moved nuclear weapons out of storage or raised the alert level of its nuclear forces, contrary to Russian President Vladimir Putin’s claims. Consequently, not all Europeans agree that there is a greater need than in the past to bolster European nuclear options to deter Russian threats.

But Germany’s chancellor-in-waiting, Friedrich Merz, expressed interest in a potential nuclear-sharing arrangement with France and the UK—the only two European nuclear powers. Polish Prime Minister Donald Tusk has said that Poland “is talking seriously” with Paris about being protected by the French nuclear arsenal and even floated the idea of Poland acquiring its own nuclear weapons. In response, French President Emmanuel Macron said in March that he would open strategic debate with European allies on the possibility of assigning France’s nuclear mission to the protection of others on the continent from Russian threats. These proposals are often framed in European debates as a “second insurance policy” or “nuclear safety net”—worth pursuing as a hedge, even if the United States does not abandon extended deterrence on the continent.

What is the United States’s extended nuclear deterrence policy in Europe?

The commitment to use nuclear weapons to defend allies is a key feature of U.S. declaratory nuclear policy. The 2022 Nuclear Posture Review highlights that “as long as nuclear weapons exist, the fundamental role of nuclear weapons is to deter nuclear attack on the United States, our Allies, and partners.” As a result, the U.S. nuclear force is expansive—and expensive—with around 5,044 warheads total. Its nuclear triad—which includes a sea leg (submarines), an air leg (bombers), and a land leg (intercontinental ballistic missiles, or ICBMs)—is the second-largest in the world, and Washington justifies its size partly on extended deterrence commitments to allies.

The United States also maintains an ability to “scale” nuclear attacks by having several options in yield and delivery vehicles—from large “strategic” weapons that can destroy entire cities to smaller “non-strategic” (also called “tactical”) weapons designed for battlefield use. This is a key parameter of its “tailored” strategy to deter both large-scale and limited nuclear attacks from a range of adversaries. In Europe, U.S. extended deterrence is institutionalized through NATO. Within the alliance, the United States maintains about 100 B-61 nuclear gravity bombs (for which Washington retains sole use authority) on the territories of Belgium, Germany, Italy, the Netherlands, and Türkiye as part of the Dual-Capable Aircraft (DCA) mission. However, some analysts believe that the credibility of NATO’s nuclear component relies more on Washington’s “strategic” weapons—U.S.-based ICBMs and submarine-launched ballistic missiles—in addition to its massive conventional forces—than on the DCA mission, which mainly fulfills a signaling and ally reassurance role.

NATO created a nuclear planning group in an effort to allow for more transparency on nuclear issues within the alliance and to discuss and consult with Washington and London on relevant nuclear issues (France has chosen not to participate in the group). Outside of the countries that host U.S. B-61s, NATO also provides space for nonnuclear countries to support nuclear operations without being formally part of them.

What are France’s and the UK’s nuclear policies?

France and the UK maintain comparatively limited nuclear forces. Both countries operate on the assumption that weaker nuclear powers can credibly deter major powers such as Russia so long as they maintain the capability to inflict “unacceptable” damages on their adversaries. This at least partly explains why the number of nuclear weapons in their arsenals has remained relatively stable despite the fluctuations in great powers’ arsenals.

France fields an air leg, which consists of strategic Rafales and Mirages armed with nuclear cruise missiles, and a sea leg, which includes four nuclear-powered submarines armed with ballistic missiles (SSBNs). It is estimated to have 290 nuclear warheads. The UK has what is known as a nuclear monad, with four SSBNs, and it possesses around 225 nuclear warheads total.

France and the UK have narrower concepts of deterrence than the United States, and their more limited options theoretically lead to a higher threshold for nuclear use. Paris considers that its nuclear weapons are meant to deter an attack on the country’s most vital interests, which it considers to include a “European dimension.” The UK similarly only considers using nuclear weapons in situations of extreme self-defense, which from London’s perspective can include defending NATO allies.

Since 1962, London has explicitly tied its nuclear capability to the defense of the NATO alliance, although it retains the sole authority to decide when to use nuclear weapons. France, on the other hand, has kept its nuclear forces separate from NATO to maintain its “freedom of assessment and decision-making” on this matter. While France’s nuclear force is entirely independent, the UK relies in part on the United States for the maintenance of its missiles and elements of the nuclear warheads. Although the Trump administration hasn’t made any comments on this subject yet, some defense analysts in the UK worry that if Washington stops sharing materials and technical expertise, London may struggle to replenish its reserves. In response to these fears, British Prime Minister Keir Starmer’s government has recently stressed that Washington remains a “reliable ally” and that this nuclear cooperation “has been and continues to be a considerable mutual benefit to both nations.” Unlike France, the UK has not publicly entertained European nuclear “umbrella” scenarios.

What might a French-led European nuclear mission look like?

The sheer size and diversity of the U.S. nuclear arsenal precludes a one-for-one replacement by the Europeans. France does not have nearly as many nuclear options as the United States, and it may not be able to build more in the near term, given that it dismantled the fissile material production facilities needed to increase its arsenal.

Integrating European allies in its nuclear deterrent is not straightforward for Paris. Both the far-right and the far-left in France have strongly opposed any “Europeanization” of France’s nuclear forces. The French president also does not want to share or delegate his power to decide when France’s vital interests are at risk. Paris believes it would not need to make any changes to its current posture to formally cover broader European interests—Macron argues that deterring against the overtaking of a European ally is de facto one of Paris’s vital interests—but it recognizes that this may not be enough to reassure its neighbors. So what options are on the table?  The integration of French nuclear forces into NATO’s nuclear planning group has so far been a no-go for the French establishment—at least so long as the United States remains in NATO. What is more, from the French perspective, NATO nuclear doctrine has a lower threshold for nuclear use than France’s, given that it contemplates repeated limited nuclear strikes. As a result, Paris is reluctant to link its alert levels to NATO’s—something that officials fear would happen if France became involved in the nuclear planning group.

But France has other reassurance options aside from building more capabilities or giving up sovereign decisionmaking. It could, for instance, rotate a portion of its strategic aircraft around a group of European countries. Another option could be to include nonnuclear allies in closer nuclear cooperation between France and the UK. For example, French nuclear expert and Deputy Director of the Foundation for Strategic Research Bruno Tertrais has argued that both countries could establish a joint nuclear submarine force—while still retaining full control over their own national nuclear capabilities—and coordinate their patrols. There are already efforts to create more exchanges on nuclear policy and mutual interests between London and Paris, and this collaboration is likely to intensify in the coming years. Nonnuclear states could participate in this arrangement through some form of conventional support that would involve them indirectly in the French nuclear mission. They could, for instance, provide escort aircraft for France’s nuclear fleet or join a task force with the eventual successor to the Charles de Gaulle aircraft carrier.

This type of conventional support of the French nuclear forces could help reassure allies and allow them to become more familiar with France’s nuclear forces. At the same time, this would offer a path for them to indirectly finance an increased scale of operations—for example, more frequent strategic signaling to Russia through temporary deployments to the Baltics. Such indirect allied support might also alleviate domestic fears over any potential loss in independence, which remains a crucial element of France’s strategic DNA.

Would French extended nuclear deterrence guarantees reassure European frontline states?

Macron and his predecessors have repeatedly stated that France’s vital interests have a “European dimension.” The notion of vital interests is kept vague on purpose to discourage adversaries from attacking right below the nuclear threshold and to give enough leeway for the president to decide when the country’s vital interests are in danger. The French president also seems confident that Europe can deter large-scale attacks without the need for U.S. nuclear security guarantees. He has stated, “We have credibility because today, among the European countries that are members of NATO, there are two fully European nuclear powers.”

France’s tendency to take unilateral decisions and to openly voice views that go against European and NATO consensus have at times damaged its reputation as a trustworthy European ally. The 2027 French elections, in which anti-European forces could win out, are also looming large in allies’ minds. Nevertheless, most believe that France would feel directly threatened by a full-scale invasion or destruction of another European country, especially a neighbor, because of the high level of economic interdependence that has resulted from European integration.

But questions arise over how French and British nuclear planners view lower-level threats to European countries, especially those further away. In a situation in which Paris and London would be both unable and unwilling to climb up the nuclear escalation ladder with Moscow (with a much larger and more flexible arsenal than both countries combined), only a strong conventional military presence would allow Europe to defend these states and deter further escalation down the line. In this context, the potential drawdown or departure of the U.S. conventional military personnel from Europe presents an acute and immediate concern. Thus, to effectively deter Russian aggression, designing a European nuclear umbrella is not enough—Europeans must focus on reinforcing their conventional forces.

What would be the implications of nuclear proliferation in Europe?  

All European states are party to the major nonproliferation treaty and would likely move to withdraw if they were to pursue nuclear weapons. A state may be allowed to withdraw from the treaty—after giving three months’ notice—if the UN Security Council concurs with its judgment that “extraordinary events . . . have jeopardized the supreme interests of its country.” The proliferating state might still be breaking other laws or commitments, depending on the technical character of its nuclear programs. For instance, it could be breaking peaceful uses commitments to suppliers of its nuclear fuel or reactor technology, which could trigger punitive international responses.

Aside from considerations of international law, the proliferating state must remember that building nuclear weapons takes years and requires expensive materials, facilities, and expert knowledge. Building a few nuclear explosives will not give it a survivable nuclear force—for that, it would need enough weapons that could be hidden or launched before an adversary such as Russia could destroy them. During the intermediate period, the country would be highly vulnerable to sabotage, assassinations of key personnel, and other forms of attack aimed at disabling its nuclear program.

Would Washington, Paris, or London protect a European country on the path to proliferation? For decades, preventing European nuclear proliferation has been an explicit objective of U.S. extended deterrence. Trump’s nominees have recently entertained different ideas about the desirability of “friendly” proliferation but have not commented on whether or how the United States would protect “friends” in the process of acquiring their own nuclear weapons. Paris and London are unlikely to support such efforts.

The temptation for vulnerable countries to speculate about “going nuclear” is understandable. The details about how this could be done and what the likely risks and costs would be—compared with alternative defense and diplomatic strategies—remain to be seriously addressed.