On 25 June, the United Kingdom announced at the NATO summit in The Hague that it would purchase 12 F-35A fighter jets from the U.S. due to their ability to carry American nuclear bombs. In mid-July, for the first time in over 15 years, the U.S. probably redeployed such weapons on British territory. This is indicated by the flight of special transport aircraft from the largest nuclear warhead storage site in the U.S. (Kirtland, New Mexico) to the Lakenheath airbase in eastern England. American aircraft capable of carrying these weapons are stationed there.

The British announcement means that, for the first time since the Cold War, the number of countries with aircraft certified to carry American nuclear weapons will increase. In light of their apparent deployment in the UK, it can also be assumed that in the first time in decades, both the number of U.S. nuclear warheads in Europe and their deployment locations have increased. Until recently, it was estimated that a total of around 100 U.S. nuclear bombs were stationed at six bases in Belgium, the Netherlands, Germany, Italy, and Turkey. As with these countries, which participate in nuclear-sharing, the UK will only be able to use American nuclear weapons if the U.S. president approves it during a conflict. The United Kingdom also has its own nuclear arsenal (around 260 warheads), albeit significantly smaller than that of the United States (some 3,700 warheads), while close in size to that of France (around 290 warheads).

A (Partial) Return to the Past

 The U.S. first deployed nuclear weapons in the UK in the mid-1950s. A few years later, the two countries signed agreements allowing the British military to use some of them. The U.S. withdrew the nuclear warheads intended for UK forces in the early 1990s, while the last ones assigned to American units left the UK later, most likely from Lakenheath in 2008.

The British government declares the purchase of the F-35A a contribution to NATO’s nuclear mission. Under it, NATO members jointly plan and exercise the use of U.S. nuclear weapons stationed in Europe. All allies can also provide conventional support, such as escort, to aircraft carrying nuclear weapons. Such a joint nuclear operation could be launched if agreed upon by the entire Alliance (with the exception of France, which does not participate in NATO’s nuclear planning).

The UK’s return to nuclear-sharing may entail the deployment of more U.S. nuclear warheads in addition to those already likely to have been transferred. British F-35A aircraft are due to be deployed to the Marham base in a few years, rather than to Lakenheath, which is 25 km away. The nuclear bombs that have been apparently deployed to Lakenheath are likely assigned for use by U.S. Air Force F-35A aircraft stationed there (the base also hosts F-15E, which are nuclear-capable as well, but the U.S. is planning to withdraw them). The U.S. has been preparing this base for the potential return of nuclear weapons since 2022 by modernising special vaults in hardened hangars and expanding other infrastructure. Similar investments would be needed to station nuclear weapons in Marham, which hosted British W177 nuclear bombs, which were withdrawn from service in 1998. Nevertheless, it cannot be ruled out that British F-35As will serve as a reserve force to carry the bombs from Lakenheath if the U.S. aircraft were destroyed or otherwise unavailable. In any case, there will be significantly fewer U.S. nuclear weapons in the UK than during the Cold War. During most of that period the U.S. maintained at least several hundred nuclear warheads of various types there (not only gravity bombs but also artillery shells and warheads for short- and medium-range missiles and other systems). At that time, NATO planners foresaw the use of large nuclear forces in Europe to try to stop an invasion by the numerically superior Warsaw Pact forces.

Transatlantic, More Flexible, and Cheaper Deterrence

 The British purchase of the F-35A is intended to strengthen deterrence against Russia, especially against the limited use of nuclear weapons to coerce NATO to stop fighting. Such Russian concepts were cited as arguments for increasing the UK’s contribution to the Alliance’s nuclear mission in the Strategic Defence Review (SDR) published by the UK Ministry of Defence on 2 June. The stealthy F-35As carrying relatively low-yield nuclear bombs would be a more adequate means of response to such an attack than submarine-launched intercontinental ballistic missiles. Such missiles are currently the only system for delivering the UK’s own nuclear warheads. They are primarily intended for mass nuclear retaliation, which increases concerns that even the use of one or a few of them will be interpreted by an enemy as the beginning of a larger strike and provoke further escalation.

As in the past, the UK most likely sees participation in nuclear-sharing with the U.S. as a relatively inexpensive way to strengthen nuclear deterrence. The purchase of 12 F-35As will also take less time than the production of new nuclear bombs or missiles by the UK. Work on the next generation of ballistic missile submarines and new nuclear warheads for these missiles is already a heavy burden on the UK’s budget and nuclear enterprise. This is not changed by the fact that both the submarines and warheads will partly rely on U.S. technology. In addition, the U.S. leases ballistic missiles to the UK and services them. Under a 1962 agreement, this support is conditional on the missiles being available for use in accordance with NATO plans (although this does not deprive the British prime minister of the exclusive right to decide on their use).

The return to nuclear-sharing is also consistent with the longstanding British view of nuclear cooperation with the United States as a means of strengthening transatlantic ties. The SDR called for the United Kingdom to take the lead in increasing European support for American nuclear deterrence, as it is increasingly under strain, given not only Russia’s aggressive policy and expansion of its already large nuclear arsenal but also China’s rapid build-up of nuclear forces. Nonetheless, the British government does not publicly question the reliability of the U.S. as an ally, nor did it when the UK acquired its own nuclear weapons in the 1950s. This distinguishes the United Kingdom from France, which justified its nuclear programme exactly by doubts about the U.S. credibility and today openly articulates its concerns about possible American withdrawal from Europe. Nevertheless, France and the United Kingdom announced in July that they would cooperate in strengthening nuclear deterrence in Europe as a supplement to U.S. efforts.

Implications for Poland

 The United Kingdom’s return to nuclear-sharing and the presumed deployment of U.S. nuclear bombs on its territory will strengthen NATO nuclear capabilities. The more U.S. nuclear warheads and aircraft capable of delivering them in Europe, the more difficult it would be for Russia to try to destroy these forces. The effectiveness of NATO’s nuclear mission is becoming even more important given the growing risk of the availability of U.S. nuclear forces for operations in Europe being limited in the event of a war in the Indo-Pacific.

The strengthening of U.S.-British nuclear cooperation also indicates the that the Donald Trump administration is interested in strengthening NATO’s nuclear deterrence, despite its signals of an upcoming reduction of American conventional forces in Europe. Without U.S. government consent, neither the UK’s purchase of F-35A aircraft and its announced return to NATO’s nuclear mission, nor the deployment of U.S. nuclear weapons in Great Britain would have been possible. As a result, there is a growing likelihood that allied participation in nuclear-sharing will grow further, which would also be in line with Trump’s calls for the Europeans to  take greater responsibility for their own security.

However, it is uncertain whether the U.S. will agree to include Poland in nuclear-sharing. Not only would this be more complicated than in the case of the United Kingdom, which had already participated in the programme and has necessary agreements in place, it also retained some nuclear bomb storage facilities. More importantly, there are still concerns among NATO members, including in the U.S. administration, that the deployment of nuclear weapons in the eastern part of NATO would leave them too vulnerable to attack and escalate tensions with Russia (even though Russia has been intensifying its hostile actions anyway and all nuclear bases in Europe are vulnerable to missile attack). A more realistic way for Poland to join nuclear-sharing therefore remains the certification of the ordered F-35A aircraft to carry U.S. nuclear weapons, but without stationing the bombs at Polish bases. In that case, Polish F-35As would have to take nuclear weapons from Western Europe, if necessary, unless they were moved to Poland during a crisis (the U.S. is developing special containers for bombs for such deployments). The permanent stationing of U.S. bombs in Poland would allow them to strike targets in the Russian mainland more quickly and easily. Due to the range of the F-35A, a similar mission by the British Air Force would require either midair-refuelling by allies or making stopovers at allied airfields.