The US Air Force is examining the feasibility of a nuclear-powered version of an unmanned aircraft. The USAF hopes that such a vehicle will be able to “loiter” in the air for months without refuelling, striking at will when a target comes into its sights.

But the idea is bound to raise serious concerns about the wisdom of flying radioactive material in a combat aircraft. If shot down, for instance, would an anti-aircraft gunner in effect be detonating a dirty bomb?

It raises political questions, too. Having Unmanned Aerial Vehicles (UAVs) almost constantly flying over a region would amount to a new form of military intimidation, especially if they were armed, says Ian Bellamy, an arms control expert at Lancaster University in Britain.