Can France and the UK Replace the US Nuclear Guarantee in Europe?

The United States is no longer the credible ally it once was. Threats of war against Denmark to seize Greenland, calls for Spain to be expelled from NATO, talk of asking Putin to invade European countries that failed to spend enough on defence, the inclusion of the EU as an enemy to be confronted in the 2025 National Security Strategy, which also states that the United States would interfere in the domestic elections of European countries by supporting the “Patriots”, as we saw Elon Musk do at AfD rallies. The United States has not only ceased to be the reliable ally it once was; it has become, perhaps not an enemy, but certainly a security and stability problem for all Europeans.

Of all the dimensions of security affected by this loss of trust, the most important is probably nuclear deterrence. Since the Cold War, Europe’s nuclear architecture has rested on three unequal pillars: the United States, the United Kingdom and France. Yet only Washington has built a genuine architecture of extended deterrence in Europe, through nuclear sharing, dual-key arrangements and NATO’s Nuclear Planning Group.

The question is therefore straightforward: if the US guarantee ceases to be credible, can France and the United Kingdom replace it, wholly or partially, and provide Europe with an autonomous nuclear deterrent? This is a question I examine in greater detail in a recent article in Comparative Strategy, comparing the evolution of French and British nuclear doctrines and their implications for European security.

The answer is uneven. The United Kingdom possesses a credible nuclear force, but its doctrine is fully integrated into NATO and has in recent years reinforced an explicitly “NATO First” policy. Its contribution to European extended deterrence takes place exclusively within this organisation, while its system also retains a structural technological dependence on the United States, particularly through the Trident missiles.

There is also a decisive material limitation. The British nuclear force is exclusively submarine-based and lacks an airborne nuclear component. This makes it impossible to reproduce outside NATO arrangements similar to US nuclear sharing. Consequently, with its current capabilities, extended deterrence led or backed by the United Kingdom outside NATO is not only politically unlikely, but technically unfeasible.

France is in a different position. Its deterrent is built around strategic autonomy and is neither technologically nor doctrinally dependent on the United States. In addition to its submarine force, it maintains an airborne nuclear component, giving it options that are unavailable to the United Kingdom. Technically, France could contemplate deploying nuclear-capable aircraft on allied territory or establishing some form of nuclear-sharing arrangement.

There is also a doctrinal difference. For decades, France has recognised a European dimension to its vital interests and, particularly under Emmanuel Macron’s presidency, has shown a growing willingness to discuss the role of its deterrent in European security. Yet this doctrinal latitude and these technical capabilities do not yet constitute a credible extended deterrence guarantee. France has established neither formal nuclear guarantees for other European states, nor joint planning mechanisms, nor institutionalised consultation structures. The European dimension of its deterrent remains subordinated to vital interests defined sovereignly by France.

Therefore, a Franco-British guarantee, whether parallel or coordinated, cannot in its current configuration constitute credible extended deterrence for third European states. French capabilities offer possibilities that British capabilities do not, but a genuine European deterrent would require a multinational and institutionalised architecture, a coordinated doctrine, joint planning, transparent commitments and collective decision-making mechanisms.

Disclaimer: Views expressed are of the author(s) and do not necessarily reflect the views of The Statecraft Institute.