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.