Losing the U.S. Nuclear Umbrella: Can Europe Compensate for a U.S. Exit?

As the United States withdraws from Europe, NATO may lose a large part of its nuclear arsenal.

Picture: U.S. Department of Defense

The first weeks of the Trump administration have put the United States and Europe on a confrontational path. If the United States were to withdraw from NATO or formally declare that it would no longer protect Europe, European NATO states would lose access to the U.S. nuclear arsenal for extended deterrence.

In this post, I examine the implications the U.S. nuclear arsenal disappearing from the European continent would have for its security architecture.

The U.S. nuclear arsenal

The United States currently provides the bulk of NATO’s strategic and non-strategic (or “tactical”) nuclear capabilities. It is estimated to deploy around 1,700 nuclear warheads.

This includes (warhead yield in brackets):

• ICBMs: 200 W78 (335 kT) and 200 W87 (300 kT) warheads on silo-based LGM-130G Minuteman III intercontinental ballistic missiles.

• SLBMs: 384 W88 (455 kT), 561 W76-1 (90 kT), and 25 W76-2 (8 kT) warheads on UGM-133A Trident II D5/LE submarine-launched ballistic missiles.

• ALCMs: 200 W80-1 (5-150 kT) warheads on AGM-86 air-launched cruise missiles.

• Gravity Bombs: 100 B61 (50-170 kT) and B83 (1-1,200 kT) nuclear gravity bombs for delivery by designated B-2A Spirit bombers.

Additionally, the U.S. forward deploys around 100 B61 (50-170 kT) nuclear gravity bombs in Europe, with 60 earmarked for delivery by NATO ‘dual-capable aircraft’ from Belgium, Germany, Italy, the Netherlands, and Turkey.

If the United States were to leave NATO or simply declare its unwillingness to support NATO member states, NATO would lose access to this nuclear arsenal.

Nuclear missions

The U.S. nuclear arsenal serves two functions that European nuclear forces cannot fully replicate at present: damage limitation and nuclear warfighting below the strategic level.

Damage limitation

Damage limitation involves preemptive nuclear strikes against an adversary's nuclear forces, command and control infrastructure, and delivery systems to reduce their ability to launch a full-scale attack. Such operations require advanced intelligence, surveillance, and reconnaissance (ISR) capabilities, a sufficiently large arsenal to saturate enemy targets, and highly accurate delivery systems to maximize the kill probability of individual warheads.

While not officially acknowledged—though the U.S. occasionally hints at it more explicitly—the American nuclear arsenal is, in many respects, optimized for damage limitation strikes, particularly compared to the French and British nuclear deterrents.

The latter are insufficient, especially in size. France and the UK together deploy approximately 515 nuclear warheads, which would likely be inadequate to target Russia's land-based nuclear forces for damage limitation purposes. Moreover, France and the United Kingdom lag significantly behind the United States in terms of anti-submarine warfare capabilities. Consequently, Russia's submarine-launched nuclear weapons would likely continue to be able to operate relatively unopposed, even if a damage limitation strike would significantly degrade its land-based nuclear arsenal.

Nuclear warfighting

Nuclear warfighting below the strategic level involves the controlled use of nuclear weapons in regional or local contingencies, typically employing low-yield warheads with selective targeting options. The goal is to achieve military and political objectives in a nuclear conflict without triggering full-scale nuclear war.

Currently, only the United States appears to be doctrinally preparing for nuclear conflict at these lower levels of the escalation ladder, while also maintaining a sufficiently diverse arsenal of delivery vehicles and warheads to support such operations.

While France has stated that the nuclear ASMP-A air-launched cruise missile serves a different purpose than its strategic SLBM arsenal—meant to deliver a final warning before potential escalation to a full-scale strategic nuclear response—, Paris does not doctrinally distinguish between strategic and non-strategic nuclear weapons. In fact, France’s nuclear doctrine does not acknowledge a ‘non-strategic’ phase in nuclear conflict in the first place.

In contrast, the United Kingdom recognizes a ‘sub-strategic’ role for its nuclear arsenal, in principle preserving the option for a limited nuclear strike. The main issue, however, is the limited arsenal depth of low-yield warheads and versatility of the British nuclear arsenal, which arguably restricts its ability to provide a sufficient range and scale of non-strategic nuclear options for nuclear warfighting. While the United Kingdom has reportedly gained access to a low-yield version of its ‘Holbrook’ nuclear warhead, its availability is likely very limited.

As such, without the U.S. nuclear arsenal, NATO would likely lose its ability to effectively compete with Russia on the sub-strategic nuclear level.

Implications for NATO’s deterrence posture

Traditionally, the United States maintained a damage limitation capability as part of a Cold War-era extended nuclear deterrence consensus. This approach discouraged European allies from developing their own nuclear weapons by credibly signaling that, if necessary, the U.S. could preemptively target the Soviet nuclear arsenal before it could be launched—including against European cities.

European nuclear powers, particularly France, have stated their willingness, in principle, to extend their nuclear deterrent to other European states as U.S. extended deterrence becomes increasingly uncertain. However, unlike the U.S. nuclear umbrella, the French deterrent lacks a credible damage limitation capability. In essence, France is offering retaliation on behalf of its allies once their existence as sovereign entities faces an immediate existential threat.

This pledge may be somewhat credible for states near France, such as Germany, Belgium, or the Netherlands, where an existential threat to their capitals would likely also threaten Paris. However, it is a much harder sell for countries like Finland or the Baltic states, which are geographically distant from France’s borders.

For both France and the UK, acquiring a nuclear damage limitation capability in the short or medium term is unrealistic—and likely undesirable. To be clear, the extent to which losing access to a credible nuclear damage limitation or warfighting capability would weaken NATO’s overall deterrence posture is a question that remains hotly debated. While answering it is beyond the scope of this post, what is clear is that it would reshape Europe’s extended deterrence architecture.

The implications of losing access to American nuclear warfighting capabilities are perhaps more straightforward.

Analysts frequently debate whether a non-strategic nuclear arsenal is necessary to deter an adversary’s non-strategic nuclear forces, and resolving this debate is again beyond what this post is aiming for. However, it is clear that unlike European nuclear-powers, Russia places significant emphasis on non-strategic nuclear options, both in doctrine and procurement priorities.

In my view, a scenario in which Russia retains multiple options for managing escalation at the sub-strategic nuclear level while European NATO states have very limited ways of responding could create dangerous ‘deterrence gaps’. If Russia believes it can outmaneuver its European adversaries by escalating to non-strategic nuclear use while European nuclear weapon states lack viable response options, it may be tempted to exploit this asymmetry. Russian publications on the subject suggest that this kind of thinking is not just hypothetical.

To address this, European nuclear weapon states may need to invest more in their own non-strategic nuclear options and adapt their doctrines accordingly, especially if the U.S. nuclear arsenal were to vanish from the continent. At present, however, both France and the United Kingdom appear to lack the motivation to take such steps.