Germany’s next chancellor, Friedrich Merz, set European pigeons flying in circles when he suggested last month that given rising mistrust in President Trump’s commitment to NATO, he wanted to talk to France and Britain about extending nuclear deterrence over Germany.
Warning that a “profound change of American geopolitics” had put Poland, as well as Ukraine, in an “objectively more difficult situation,” Prime Minister Donald Tusk of Poland suggested the same, while hinting that Poland, with its long history of Russian occupation, might eventually develop its own bomb.
Then Poland’s president, Andrzej Duda, said this week that it was time for the United States to consider redeploying some of its nuclear weapons from Western Europe to Poland. “I think it’s not only that the time has come, but that it would be safer if those weapons were already here,” Mr. Duda told the Financial Times.
The uproar was immediate, given the sensitivity and complications of the nuclear issue and the whole concept of extended deterrence — the willingness of a nuclear-armed country to use its nuclear weapons in defense of a nonnuclear ally. That commitment is at the heart of NATO’s Article Five, promising collective defense, and hinges on the massive American nuclear arsenal.
Mr. Trump and his officials say they remain committed to extending the American nuclear umbrella over Europe, the vital deterrent to any serious Russian aggression, and to the alliance itself. But his evident hostility toward Europe has so unnerved America’s traditional European allies that it has provoked strong doubts that they can depend on the United States.
There are fears that talking too much about a European replacement, let alone trying to construct one, would only encourage Mr. Trump to withdraw his pledge. Even so, European allies are now engaged in the most serious debate in generations about what Europe’s nuclear defense should be.
Like many things when it comes to European defense, replacing the American commitment would not be easy.
Today France and Britain are the only two Western powers in Europe who possess nuclear weapons. For others, like Germany, to join the nuclear club would be expensive, require leaving the Nuclear Nonproliferation Treaty and could seem more threatening to Moscow, raising risks rather than lowering them.
But together, the French and British have only about 500 warheads compared with some 3,700 in the American arsenal, with another 1,300 or so waiting to be deactivated. The Americans also have what is known as the “triad” — nuclear weapons on land-based missiles, bombers and submarines.
The French have no land-based missiles but do have nuclear-equipped bombers and submarines, while the British have only submarines.
And only the French nuclear arsenal is truly independent of the United States, technically and politically. France has always refused to join NATO’s nuclear planning group, keeping sole authority on the use of its weapons in the hands of the French president, currently Emmanuel Macron.
The British deterrent depends on American Trident II missiles, launching mechanisms and maintenance, raising at least the question of whether the British government has full authority to launch these weapons.
French doctrine has always been kept a bit vague, part of the uncertainty that is the heart of deterrence. “We have a pretty good idea what the French will not do, but not such a clear understanding of what they are willing to do,” said Claudia Major, head of trans-Atlantic security studies for the German Marshall Fund.
Since 2020, Mr. Macron has sometimes spoken of France’s vital national interests as having “a European dimension,” without specifying what that is. Earlier this month, he announced a “strategic debate on using our deterrence to protect our allies on the European continent.”
“But how far does that ‘European dimension’ go?” Ms. Major asked. “The French won’t define it and of course don’t want Russia to know.”
The security of neighboring Germany and perhaps Poland would likely qualify as vital French national interests, said Erik Jones, director of the Robert Schuman Center at the European University Institute.
But it is far from clear that a quick conventional Russian attack on Estonia or Lithuania would prompt a French nuclear threat or response. “The vital interests of France do not reach that far,” he said.
The French nuclear deterrent is not meant to provide an American-style extended deterrence on the cheap, said Camille Grand, a former French and NATO defense official. But it does provide another degree of uncertainty for Moscow that complements and even strengthens NATO nuclear policy, he said.
Since both France and Britain are European, their national interests are more likely to stretch to the European neighborhood than is the case for the distant United States, Mr. Grand argued.
Then there is the question of the next French president. Should it be Marine Le Pen, the head of the far-right National Rally, she might have a narrower view of French interests. That could undermine the credibility of an extended French nuclear deterrent in the same way that Europeans have become anxious over Mr. Trump’s commitment.
Still, with both bombers and submarines, France maintains an “escalation ladder,” with the ability to threaten use without doing so. For example, in February 2022, after the Russian invasion of Ukraine, France put a third nuclear submarine out to sea, “a quiet but explicit message that the Russians saw,” Mr. Grand said.
As Mr. Merz and the Polish leaders suggested, France might also consider “nuclear sharing,” as the Americans now do. There are five European countries — Germany, Italy, Belgium, the Netherlands and Turkey — that currently host American B61 nuclear bombs and have their own airplanes to deliver them.
Poland would like to be a sixth. While French nuclear-capable bombers have been refueled by Italy, for instance, for France to decide to place some of its nuclear weapons and bombers in other countries would be a break with its current doctrine. In any case, France and its president would retain total control over their use.
Submarines by themselves do not provide an escalation ladder, because they are supposed to remain hidden, and either fire missiles or don’t. That is one reason British officials are considering restoring the air leg of their deterrent. Ideally, the British would also benefit from another nuclear-capable submarine, so more than one can be at sea. But the expense is enormous.
And there is no way to share a submarine with another country, the way an air-launched bomb or missile can be shared.
In the end, the core of NATO’s nuclear deterrent remains the United States, said Ivo Daalder, a former U.S. ambassador to NATO.
The question for him is less the number of warheads than the credibility of the deterrence. “How to make a deterrent versus Russia credible when you’re an ocean away and convince allies you’re willing to make the ultimate sacrifice for them?” he asked. “Unfortunately, Trump answers those questions without even raising them.”
Given all the uncertainty, Germany might have to go nuclear itself, said Thorsten Benner, director of the Global Public Policy Institute. “So far talk of a German bomb has been limited to fringe types, but now it becomes more mainstream,” he said. But he prefers discussing nuclear sharing with France, with French bombers on German bases.
Matthew Kroenig, a former defense department official who directs the Scowcroft Center for Strategy and Security at the Atlantic Council, thinks the debate has been beneficial to get Europeans to take defense more seriously.
“NATO allies should do a lot more of the nuts and bolts of conventional defense, but some high-end stuff like nuclear deterrence — only the United States can provide,” he said.
Ms. Major has another concern, widely shared. “The more we do for defense the better for us,” she said. “But does it send the wrong signal and have the unintended consequence of America leaving? It’s the decoupling argument that we fear so much.”
