This article is more than 2 years old

This article is more than 2 years old

The US is to spend billions of dollars upgrading 150 nuclear bombs positioned in Europe, although the weapons may be useless as a deterrent and a potentially catastrophic security liability, according to a new report by arms experts.

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A third of the B61 bombs in Europe under joint US and Nato control are thought to be kept at Incirlik base in Turkey, 70 miles from the Syrian border, which has been the subject of serious concerns.

The threat to the base posed by Islamic State militants was considered serious enough in March 2016 to evacuate the families of military officers.

During a coup attempt four months later, Turkish authorities locked down the base and cut its electricity. The Turkish commanding officer at Incirlik was arrested for his alleged role in the plot.

A report on the future of the B61 bombs by arms control advocacy group the Nuclear Threat Initiative (NTI) , made available to the Guardian, said the 2016 events show “just how quickly assumptions about the safety and security of US nuclear weapons stored abroad can change”.

Since then, US-Turkish relations have soured further, largely over Washington’s support for Kurd forces in Syria. The national security adviser, HR McMaster, and secretary of state, Rex Tillerson, have made trips to Turkey this week to try to heal the rift.

There have been reports that the bombs have been quietly moved out because of safety concerns, but that has not been confirmed.

The remaining B61 bombs are stored at five other locations in four countries: Italy, the Netherlands, Belgium and Germany, according to the Federation of American Scientists, which tracks the weapons. The NTI report said it “should be assumed that they are targets for terrorism and theft”.

The bombs are the remnants of a much larger cold war nuclear arsenal in Europe, and critics have said they serve no military purpose, as the nuclear deterrent against Russia relies largely on the overwhelming US strategic missile arsenal.

Using the B61s in any conflict would involve an agreement between the US and the host country in consultation with other Nato members.

“It is hard to envision the circumstances under which a US president would initiate nuclear use for the first time in more than 70 years with a Nato [dual-capable aircraft] flown by non-US pilots delivering a US B61 bomb,” said the NTI report, titled Building a Safe, Secure and Credible Nato Nuclear Posture.

Since the cold war, the B61 has played a symbolic role, as reassurance for some Nato members of US commitment to defending Europe. They are also considered potential bargaining chips against Russia’s much greater arsenal of nearly 2,000 tactical nuclear weapons.

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However, the NTI report argues they are also serious liabilities, because of the threat of terrorism or accident, and because they could become targets in the early stages of any conflict with Russia.

“Forward-deployed US nuclear weapons in Europe increase the risk of accidents, blunders, or catastrophic terrorism and invite pre-emption. Given these added risks, it is past time to revisit whether these forward-based weapons are essential for military deterrence and political reassurance,” the Obama administration energy secretary Ernest Moniz and the former Democratic senator Sam Nunn, both NTI co-chairmen, argue in the preface to the report.

The Obama administration considered withdrawing the B61s from Europe as part of the president’s nuclear disarmament initiative but the idea lost support as relations with Russia deteriorated. Instead, the administration approved a Pentagon programme to upgrade the bombs over the next decade with a tailfin assembly to make them more accurate.

The plan has been embraced by the Trump administration’s nuclear posture review, despite the fact that the estimated cost of the 460 new model B61-12 bombs – including 310 in the US – has doubled in recent years to $10bn, a part of a huge increase of overall defence spending.