In reply to damhan-allaidh:
Surely an explanation of what our navy does is very simple... either:
The marine division of our armed forces. Their duties include:
Patroling the coastal waters of Britain and her territories,
maintaining "the law of the sea" - anti drug and piracy operations
Humanitarian relief - e.g. Tsunami, Haiti etc
Off shore offensive support, missile platforms and floating hospitals, air craft carriers (if we have any left) - e.g. Libya
Maintaining Supply lines to other armed forces
Nuclear deterrent - Trident
The last line of defense - Will launch nukes at our enemies after the government has been annihilated (and Radio 4 stops broadcasting)
Or in other words Tinkers, Tailors, Soldiers and spies