The whereabouts of Britain's nuclear-armed submarines are one of the nation's most closely guarded secrets. One of the four Vanguard-Class submarines that carry Britain's nuclear deterrent continuously patrols the seas, ready to fire Trident missiles on the Prime Minister's command. Only four people aboard know its route, and its location is kept secret for the length of its deployment. It stays silent as it makes its slow, stealthy passage deep beneath the waves, receiving only incoming