Military bunkers in the UK are being upgraded so they can be used to store US nuclear weapons again after 14 years of standing empty, according to US defence budget documents. In the Biden administration’s 2023 defence budget request, the UK was added to the list of countries where infrastructure investment is under way at “special weapons” storage sites, alongside Belgium, Germany, Italy, the Netherlands and Turkey – all countries where the US stores an estimated 100 B61 nuclear bombs. Hans Kristensen, the director of the nuclear information project at the Federation of American Scientists (FAS), who first reported on the budget item, said he believed the British site being upgraded is the US airbase at RAF Lakenheath, 100 km north-east of London. The US withdrew its B61 munitions from Lakenheath in 2008, marking the end of more than half a century of maintaining a US nuclear stockpile in the UK. At the time of the withdrawal, the gravity bombs were widely seen as militarily obsolete and hopes were higher for further disarmament by the nuclear weapons powers. That optimism has since been dashed, against the backdrop of Vladimir Putin’s invasion of Ukraine, his regime’s nuclear threats against Nato, and extensive nuclear weapon modernisation programmes pursued by both the US and Russia. As part of the US plan, the B61 has been given a new lease of life with a guidance system, the B61-12 variant, due to go into full production in May. The 2023 budget request says that Nato “is wrapping up a 13-year, $384m infrastructure investment program at storage sites in Belgium, Germany, Italy, the Netherlands, the UK, and Turkey to upgrade security measures, communication systems, and facilities”. In the 1990s, RAF Lakenheath had 33 underground storage vaults, where 110 B61 bombs were stored, according to the FAS. Since their withdrawal the vaults have been mothballed. Kristensen said he believes the vaults are now being upgraded so the new B61-12 bombs can be stored there, if needed. The Biden administration has been careful not to make any moves that might be seen as escalatory in the nuclear arena in response to Putin’s announcement he would put Russia’s nuclear forces on higher alert a few days after his invasion of Ukraine. The US has cancelled scheduled tests of its intercontinental ballistic missiles, for example. For the same reason, Kristensen said he doubted the Biden administration is planning to increase the US nuclear stockpile in Europe. When the new B61-12 bombs are delivered, expected next year, they will replace older models already there. Instead, he thought the Lakenheath upgrade is intended to provided more flexibility to move the nuclear weapons around Europe. “One of the things they have talked about is protecting the deterrent against Russia’s improved cruise missiles capabilities,” Kristensen said. “So they could be trying to beef up the readiness of more sites without them necessarily receiving nukes, so that they have the options to move things around in a contingency if they need to.” Britain has become keen to take a more assertive role when it comes to its own nuclear deterrent, and last year announced it would increase its own stockpile of Trident nuclear warheads by 40% to 260, the first such increase since the end of the cold war. Whitehall sources say the UK has “a clearer appreciation” of its role as a nuclear weapons state in a renewed era of state competition with Russia and China. The UK Ministry of Defence did not comment on the upgrade mentioned in the US budget. One British official said: “We won’t provide anything on this as it relates to the storage of nuclear weapons.” But the news comes just four months after the arrival in Lakenheath of the first of a new generation of nuclear-capable US combat aircraft, the F-35A Lightning II, the first such deployment in Europe. Daryl Kimball, the executive director of the Arms Control Association, said the upgrade of the UK storage facilities is “an early sign that the US and Nato are preparing to engage in a protracted and maybe heightened standoff with Putin’s Russia”. “The administration should provide some clarity about the military necessity and goals of possibly bringing nuclear weapons back to the UK,” Kimball added. The developments in Europe are part of a broader retreat from arms control. The Biden administration’s nuclear posture review, which has been sent to Congress but not yet declassified, is reported not to contain the changes the president pledged during his campaign. In 2020, he said he would formally declare the sole purpose of nuclear weapons to be deterrence of a nuclear attack against the United States or its allies. But the review leaves open the option of using nuclear arms to respond to non-nuclear threats as well. The nuclear disarmament group CND said the “quiet announcement” by the US amounted to more militarisation at a time of growing risk and would add to the risks faced by the British public. Kate Hudson, the general secretary of CND, said she feared it could lead to US warheads being redeployed in the UK. “Nuclear weapons don’t make us safe – they make us a target,” she added.