18-07-2025
As US support for NATO wobbles, France and UK strengthen nuclear ties
Last week, British Prime Minister Sir Keir Starmer and French President Emmanuel Macron signed the 'Northwood Declaration' committing themselves to 'deepen their nuclear cooperation and coordination.' They announced that 'a U.K.-France Nuclear Steering Group will be established to provide political direction for this work. It will … coordinate across nuclear policy, capabilities, and operations.'
The agreement reflects growing apprehension on the part of both leaders that America's commitment to NATO is no longer as strong as it once was, at the very time that Vladimir Putin's Russia poses the greatest security threat to Europe since the Cold War.
This fear is explicitly reflected in their respective updated national security strategies. Britain issued its 'Strategic Defence Review' on June 2 and France released its national strategic review on Bastille Day, July 14. Both documents have almost identical language when discussing the Russian threat, both stress the importance of their 'independent' nuclear deterrents to European security and both mention their growing cooperation and reference the Northwood Declaration.
This is not the first time London and Paris have committed themselves to work more closely on strategic nuclear matters. As the U.K. review notes, 'The 1995 Chequers Declaration stated that there is no situation in which a threat to a vital interest of one is not a threat to both.'
In reality, in the three decades since that earlier declaration, not all that much changed in the strategic nuclear ties between France and the U.K., despite some progress in the 2010 Lancaster House agreements. The reason is that there are fundamental differences between the nature of the two deterrents that are difficult to overcome.
The British nuclear deterrent has been closely tied to that of the U.S. since the 1950s. A 1958 mutual defense treaty between the two countries (updated in 2014 and extended indefinitely in 2024) provides for the transfer of classified nuclear information, fissile material and technology from the U.S. to the U.K. and for Britain to use American testing infrastructure.
But the history here is complicated. In December 1962, Secretary of Defense Robert McNamara, who in June of that year had called independent nuclear capabilities 'dangerous, expensive, prone to obsolescence and lacking in credibility as a deterrent,' canceled the air-to-surface nuclear Skybolt missile that Britain had planned to purchase from the U.S. Within days of the cancellation, and fearing that Washington wanted to undermine Britain's deterrent, Prime Minister Harold Macmillan reached an understanding with President John F. Kennedy that British nuclear forces would be based on American submarine-launched ballistic missiles that would carry British nuclear warheads.
At that time, Macmillan asserted Britain's freedom to act on its own 'where Her Majesty's Government may decide that supreme national interests are at stake.' Nevertheless, given Britain's dependence on America for so many aspects of its nuclear program, it is not at all clear just how independent London's strategic deterrent really is, even when its 'supreme interests are at stake.' Britain remains constrained by the 1958 treaty should it wish to 'communicate classified information or transfer or permit access to or use of materials, or equipment … to any nation' without U.S. permission. That places significant limits on potential nuclear cooperation with France.
France has no such limitations. French nuclear development has a significantly different history. The French deterrent has always been truly independent, to the degree that for decades Paris pursued a 'tous azimuts' or 'in any direction' strategy that, in theory, trained its strategic nuclear deterrent as much against the U.S. as against the Soviet Union. Unlike Britain's deterrent, which is explicitly committed to the defense of NATO, the French nuclear deterrent addresses threats to France itself, though that includes those territories in the Pacific, Indian Ocean and the Caribbean that are considered part of the French state.
In light of uncertainty regarding President Trump's commitment to Article 5 of the NATO Treaty, Macron has dropped ever-broader hints that France might extend its nuclear umbrella beyond its borders, thereby more closely aligning its strategy with that of the U.K. Notably, Macron and German Chancellor Friedrich Merz have announced the creation of a Franco-German security council, which appears to be the first step toward the creation of an extended French nuclear umbrella, though Macron has made it clear that final decision authority would remain with France. Merz has also sought a similar relationship with Britain that goes beyond London's more general commitment to NATO.
In that regard, it is significant that both Britain and France deployed their nuclear submarines in response to Moscow's implicit (and on occasion explicit) threats to employ tactical nuclear weapons against Ukraine. It is arguable that the Kremlin took note of these deployments and as a result toned down its nuclear saber-rattling.
Still, neither country is truly prepared to go it alone in the strategic nuclear realm without American support. Their forces are simply too small relative to those of Russia or, for that matter, China.
Britain and France are clearly moving closer toward real strategic nuclear coordination, despite the limitation of the 1958 treaty between Washington and London. The Northwood Declaration may indeed yield greater results than previous avowals of cooperation. Their joint deterrents may prove compelling, as they appear to have been in support of Ukraine.
Nevertheless, it is America's strategic nuclear deterrent, not those of London and Paris, that continues to undergird NATO. It is therefore crucial that Washington's commitment to support the alliance with its nuclear umbrella remain as strong as it has been since it was first extended in the early decades of the Cold War.
Dov S. Zakheim is a senior adviser at the Center for Strategic and International Studies and vice chairman of the board for the Foreign Policy Research Institute. He was undersecretary of Defense (comptroller) and chief financial officer for the Department of Defense from 2001 to 2004 and a deputy undersecretary of Defense from 1985 to 1987.
