On a sunny morning in 1966 two US Air Force planes collided and dropped four nuclear bombs near the village of Palomares in southern Spain. There was no nuclear blast, but plutonium was scattered over a wide area - and Spain is now asking the US to finish the clean-up. The US government calls nukes that go astray "Broken Arrows" and on 17 January 1966, Palomares got four of them. Overhead, at 31,0