In the Navy, most waterborne transportation is informally known as a ship. The exception being a submarine, which is usually referred to as a boat.
The USS Pennsylvania appears to be an Ohio-class ballistic missile submarine, which is one of the two main types of the Ohio-class, the other being a cruise missile submarine. The Ohio-class weighs approximated 17,000 tons, is 560 feet long, 42 feet high and 35 feet wide; they typically have a crew compliment of 15 officers and 140 enlisted sailors. The ballistic missile variant can carry up to 24 Trident II submarine-launched ballistic missiles, each missile can carry anywhere from 1 to 14 independently targeted warheads with a yield varying from 90 to 475 kilotons. The cruise missile variant can carry up to 154 Tomahawk cruise missiles, each missile armed with a conventional 1,000 pound yield warhead. Both the cruise and ballistic missile variants are also armed with four Mark 48 torpedo tubes, which in addition to torpedo's can also launch Harpoon surface to air anti-ship missiles.
Six part webisodes 'FTWD: Dead in the Water' and tells the story of the ill fated submarine 'USS Pennsylvania' and it's crew.