"On every British nuclear submarine, there is a safe. Inside that safe is another safe. And inside that safe is a handwritten letter from the British Prime Minister, to be opened only if the country has been decimated by nuclear war."From a BBC radio documentary called "The Human Button" (click to download/listen). Should the sub commander retaliate if Britain is annihilated? Surrender? Sail to Australia or America and operate under that government's direction? The letter will provide the answer. Totally fascinating stuff.