Somewhere in the deep, dark ocean, a British submarine is always on patrol. Silent, secret, able to stay underwater for months at a time, it carries Trident nuclear missiles that can fly thousand miles to their targets and kill millions of people at once. The captain has the key to a safe to be opened in the event of war, if all communication with Britain has been lost. Inside is a letter from the Prime Minister of the day, giving orders as to when the missiles should be fired.
Source: Trident: What the future holds for the UK’s nuclear submarines | Home News | News | The Independent