Joe Biden is sending adjustable, highly accurate tactical nuclear weapons to Europe as part of an £8.5billion upgrade which will send a clear signal to Vladimir Putin. The Pentagon has insisted the move is unconnected to the Russian President’s nuclear threats. But the announcement nevertheless came hours after Putin’s latest belligerent speech.The ‘dial-a-yield’ B61-12 thermonuclear bombs are so-called because their payloads can be switched between 0.3, 1.5, 10 and 50 kilotons.By comparison, the bomb which was dropped on Hiroshima in 1945 had a yield of roughly 15 kilotons.Measuring 12 feet in length, they are equipped with tailkits enabling them to deliver via plane, either as ‘dumb’ gravity bombs, or with an accuracy of 30 metres via ‘guided drop’ mode. Joe Biden’s move is not a response to Vladimir Putin’s threats, insists the Pentagon (Image: GETTY) Liz Truss resigned as UK Prime Minister last week (Image: GETTY)The deployment is connected to a $10billion (£8.5billion) upgrade of the US nuclear arsenal, specifically to its B61-class unguided nuclear bombs, first rolled out in 1968. At the moment, 100 B61s are stored at bases across Europe, including Germany and Italy.The weapons, which can be dropped using B-2 stealth bombers, F-15s, F-35s and Tornadoes, have had “all of the bomb’s nuclear and non-nuclear components” either replaced or refurbished, the US energy department confirmed.The process is due to get underway in December, having been brought forward in the spring, suggesting the US was responding the several nuclear threats made by Putin since the start of the war, with allies informed in September.JUST IN: Putin hails ‘close friend’ Xi and supports claim to Taiwan Russian President Vladimir Putin speaks at the Valdai International Discussion Club yesterday (Image: GETTY)Nevertheless, the Pentagon insisted the process ‘was in no way linked to current events in Ukraine and was not sped up in any way’, pointing out that the modernisation of B61s had been “underway for years”.Separately, the US yesterday unveiled its National Defence Strategy, the first in four years, and its Nuclear Posture Review.The document confirmed a programme to build a new submarine-launched cruise missile, announced when Donald Trump was resident, had been cancelled.DON’T MISSHSBC issues alert as widow scammed out of £100,000 [ANALYSIS]Pensioners could get ‘7% risk-free income in retirement’ [INSIGHT]500,000 people hit with ‘acute’ pension pain after ‘turbulent 10 days’ [UPDATE] Vladimir Putin views the annual Grom nuclear drills (Image: GETTY) Sergei Shoigu accused Ukraine of plotting to explode a dirty bomb – without offering evidence (Image: GETTY)However, US defence secretary Lloyd Austin said: “I don’t think this sends any message to Putin. He understands what our capability is.”Mr Austin added: “We are certainly concerned about escalation, we have been so from the very beginning of this conflict. It would be the first time that a nuclear weapon has been used in over 70 years.”On Wednesday, Putin watched the “Grom” exercises by Russia’s strategic nuclear forces, drills which involved intercontinental ballistic missiles, long-range bombers and submarines. Russia’s nuclear arsenal mapped (Image: Express)During a lengthy rant yesterday, in which he railed about ‘western elites’, Putin said the world was in its most dangerous phase since the end of World War 2, and also accused former Prime Minister Liz Truss of threatening his country with nuclear attack.He added: ‘Someone should have corrected her. Washington could have said they have nothing to do with that.’We are facing a historic milestone.’ Lloyd Austin, the US Defense Secretary (Image: GETTY)’Ahead of us is possibly the most dangerous, unpredictable and at the same time crucial decade since the end of the Second World War.’Putin’s defence minister, Sergei Shoigu, also triggered alarm at the weekend after claiming, without evidence, that Ukraine was planning to detonate a ‘dirty bomb’ laced with nuclear material within its own territory.Tobias Ellwood, chairman of Parliament’s defence committee, responded by telling Express.co.uk Putin’s remarks were likely to be a means of paving the way for Moscow itself to explode such a device and blame Kyiv in an attempt to justify military escalation.