Nuclear weapons have not been used in anger since the United States dropped atomic bombs on Hiroshima and Nagasaki in August 1945. Yet even after the Cold War, the Bomb is still the greatest threat facing humankind. As President Bill Clinton's first secretary of defence, Les Aspin, put it: 'The Cold War is over, the Soviet Union is no more. But the post-Cold War world is decidedly not post-nuclear...