A Boat/Ship that is capable of sailing under water, Although a German term, It is correct becouse it stands for 'Underwater Boat' which it is.
Long, hard and full of seamen.
Usually belongs to a Navy and deliveres Ballistic Missiles full of Instant sunshine to a hapless enemy that pissed you right off. These are Ballistic Subs. We have 4 of these monsters.
The Royal Navys subs are based in Faslane and Plymouth, the former has a hoard of the great unwashed outside its gates and the latter is full of drunken matelots. All of the RNs subs are nuclear powered, so adding to their scaryness.
They are EXTREMELY expensive but are the navy's version of a big stick ... as long as you have a navy ... (the Afghans/iraqis dont give a fuck about subs!)