Deterrence decoupled: Rethinking Europe’s future without a U.S. nuclear umbrella

RU

At present, it remains unclear whether President Donald Trump genuinely intends to withdraw the United States from NATO. However, his administration’s stance on European security does little to inspire confidence that the U.S. would honor its alliance commitments if European NATO members were attacked.

Should the United States withdraw — either formally or informally — this would have significant ramifications for European deterrence, including at the nuclear level. The United States possesses NATO’s largest, most diverse, and most capable nuclear arsenal. Since the early Cold War, it has used this arsenal not only to deter attacks on the U.S. homeland, but also to extend nuclear deterrence over Europe and protect non-nuclear NATO states.

Without the United States, this extended deterrence framework collapses, creating major deterrence gaps. Russia, recognizing its nuclear superiority in Europe at both the strategic and non-strategic levels, could see such a moment as its opportunity to exert coercive leverage — or even take offensive action against NATO.

To prevent such a scenario and to deter Russia from pursuing conventional aggression enabled by its nuclear arsenal, NATO must find ways to compensate for the loss of U.S. extended deterrence. This article examines three potential options: a nuclear umbrella, nuclear sharing, and nuclear proliferation.

France's nuclear umbrella

French President Emmanuel Macron has proposed extending France’s nuclear umbrella over European Union member states, invoking the need to protect what he calls “vital European interests.” In essence, his offer aims to fill the extended deterrence gap left by a potential U.S. withdrawal by using France’s nuclear arsenal, without significantly altering the state and function of France’s current “Force de frappe.”

The main issue with this proposal is that, unlike the American nuclear deterrent, France’s arsenal is not designed for this role.

Compared to the U.S. nuclear force, the French arsenal is significantly smaller and is far less diverse. While the United States operationally deploys over 1,500 nuclear warheads on a broad range of delivery systems, France’s estimated 290 warheads are primarily assigned to M51.2 submarine-launched intercontinental ballistic missiles, with the remainder carried by air-launched ASMPA-R cruise missiles.

Additionally, the U.S. deterrent includes both high-yield and dedicated low-yield nuclear options on a range of air and sea-based platforms, allowing for a flexible response across the strategic and non-strategic levels. In contrast, France’s nuclear doctrine does not recognize a distinct non-strategic nuclear level, treating any nuclear use as strategic in nature. Its arsenal is assumed to consist exclusively of high-yield warheads, though exact yields remain classified.

For purposes of homeland defense, this relatively small and one-dimensional nuclear arsenal has served France well. It provides Paris with a secured second-strike capability rather than what has been referred to as “escalation dominance” – the ability to outcompete the adversary at every escalation level. However, this approach has clear limitations in the context of extended deterrence.

While the United States can offer its allies the ability to fight and potentially win a nuclear conflict at all levels, France can only promise retaliation on their behalf. This may be somewhat credible for Germany, Belgium, and other countries that are geographically close to France, as an existential threat to their security would likely threaten France existentially as well. As such, strategic nuclear use on their behalf is at least somewhat credible.

However, this logic breaks down when applied to more distant allies such as the Baltic states, Poland, or Romania. Would a French president genuinely risk inviting nuclear retaliation against France if Estonia were overrun? Decision-makers in Tallinn would likely question the credibility of such a security guarantee — and with good reason.

Nuclear sharing

To enhance the credibility of extended deterrence, European nuclear weapon states — most notably France, but potentially also the United Kingdom — could forward deploy some of their nuclear weapons to allied European countries.

This approach may resemble the U.S. nuclear sharing arrangement formalized in 1957. Under that system, NATO member states West Germany, the Netherlands, Belgium, Italy, and Turkey hosted forward-deployed U.S. nuclear weapons, which were integrated into their military platforms while ultimate launch authority remained with Washington. However, host nations with American nuclear weapons on their soil were included in consultations through the NATO Nuclear Planning Group, established in 1966.

A similar framework could emerge in Europe following a hypothetical U.S. withdrawal. For instance, France could forward deploy some of its air-launched ASMPA-R nuclear cruise missiles to NATO allies, either alongside French-operated Rafale fighter jets or by integrating them with allied aircraft such as the Eurofighter.

From a credibility standpoint, such a deployment would be particularly effective if it occurred in one or more frontline states. Forward-deployed French nuclear weapons in the Baltic region, for example, could provide a «warning shot» capability, signaling to an advancing adversary that further aggression could provoke a large-scale nuclear response. Additionally, they could provide a limited nuclear warfighting option to dislodge or repel enemy forces in the event that conventional defense measures failed.

This type of arrangement faces two major challenges — one political, the other material.

Politically, command and control over forward-deployed nuclear weapons would likely be contentious. Host states might demand a say in how and when these weapons are used, particularly if they assume some or all of the deployment costs. However, London and Paris would be unlikely to cede shared authority over their use. Furthermore, even if a compromise were reached, its durability would remain uncertain, as it could be overturned by future leadership — an issue that also applies to France’s broader nuclear umbrella proposal.

Additionally, it is unclear whether there would be alliance-wide consensus on forward deployment, particularly in frontline states, as it could fundamentally alter deterrence dynamics with Russia. Nevertheless, if multilateral agreement proved elusive, such deployments could still occur bilaterally.

Materially, it is uncertain whether France and the United Kingdom even possess enough warheads to simultaneously maintain a secure second-strike capability and forward deploy a sufficient number of nuclear weapons to ensure the credibility of any nuclear sharing arrangement. Expanding warhead stockpiles is possible, but such a step would be time-consuming and financially demanding. The same applies to the development of new warhead types, such as a French low-yield option for the ASMPA-R.

Moreover, the United Kingdom currently relies exclusively on submarine-launched intercontinental ballistic missiles, which are unsuitable for forward deployment. To contribute to a nuclear sharing arrangement, London would first need to develop an alternative delivery system that could be based on allied territory — an air-launched cruise missile, for example.

Nuclear proliferation

If neither the nuclear umbrella option nor a nuclear sharing arrangement is deemed satisfactory by European non-nuclear weapon states, and if strengthening nuclear deterrence on the continent is considered necessary, then the only remaining option would be for these states to acquire nuclear weapons themselves.

However, such a decision would present significant technical challenges and could carry serious political and military consequences.

While the technology behind nuclear weapons development is well understood, including in Europe, the infrastructure required to produce nuclear weapons— particularly the capacity to generate fissile material, whether highly enriched uranium or weapons-grade plutonium — is not necessarily available in European non-nuclear weapon states.

Some countries, such as Norway, Poland, and Germany, either do not currently deploy nuclear infrastructure or else have largely dismantled what they once had. Others, such as Sweden and Finland, maintain civilian nuclear programs, but these are deliberately designed to prevent easy diversion for military purposes. While repurposing these programs for weapons development would not be impossible, it would take time and could be technically complex, as certain key capabilities — such as plutonium reprocessing — are not currently in place and would need to be developed from scratch.

Importantly, concealing the launch of a nuclear weapons program would be extremely difficult, if not impossible. The International Atomic Energy Agency (IAEA) continuously monitors civilian nuclear infrastructure worldwide, including in Europe, to ensure that non-nuclear weapon states do not secretly pursue nuclear weapons development.

As a result, any attempt at proliferation would likely be detected, potentially leading to strong economic and political pushback in the form of sanctions. Additionally, Russia would likely view such an effort as a direct threat and might take preemptive military action — such as missile strikes — against the proliferating state’s nuclear infrastructure before it could produce a robust nuclear arsenal. This means that the short-term security risks for the proliferating state would likely be severe, even if acquiring nuclear weapons could eventually serve as a long-term guarantor of sovereignty and independence.

Finally, there would likely be adverse political consequences. One or several European states pursuing nuclear weapons would almost certainly signal the collapse of the global nuclear non-proliferation regime, potentially triggering further nuclear proliferation in regions such as Asia and the Middle East — developments that would have far-reaching implications, including for European security.

What this discussion demonstrates is that while European states have options to respond to a potential U.S. withdrawal from NATO, there are no silver bullets or quick fixes in the nuclear domain that are capable of immediately compensating for the loss of the U.S. nuclear deterrent in Europe. Different options come with their own set of technical, political, and military challenges.