Long, hard and full of seamen.
A boat that goes underwater. Better known as U-Boat (in der Kriegsmarine), or SSK (diesel-electric powered patrol submarine) or SSBN (nuclear-powered ballistic missile submarine) or SSN (nuclear-powered attack submarine). This last would probably be called a Nuclear U-Boat by Ze Germans.
Usually belongs to a Navy and fires torpedoes, Tomahawk cruise missiles and anti-ship missiles at the enemy. Without them even knowing it was there. These are attack submarines (SSN). We have several of these beasts, although numbers are stealthily diminishing as pollies spend less and less money on them - and make fewer and fewer press releases about them. The latest Astute class are several years behind schedule.
Usually belongs to a Navy (probably American, British or French) and delivers ballistic missiles full of Instant Sunshine to a hapless enemy that pissed you right off. These are nuclear-powered ballistic missile submarines (SSBN). We have 4 of these monsters, each armed with 16 Trident D-5 missiles.
The Royal Navy's subs are based in Faslane and Plymouth. The former has a horde of the great unwashed outside its gates and the latter is full of drunken matelots. All of the RN's subs are nuclear powered, so adding to their scariness; they gave up on SSKs years ago which some view as a mistake of galactic proportions.
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!) They should, but ignorance is bliss, as they say. And the sub drivers are very happy with this, as they go about their humdrum tasks - with huge inland target lists at their elbow...