The hull is the outer shell or the metal skin of the submarine
Types of Hulls -
Submarines have 2 or more hulls - the superstructure, which is the visible external hull you see, and the inner pressure hull, which contains all the primary equipment and houses the crew.
The space between the superstructure and the pressure hull is where the main ballast tanks are located, as well as line lockers, access/weapons hatches, etc.
The pressure hull is where the crew lives and works (and keeps on working...).
The primary reason there are 2 hulls is that the pressure hull, while optimally designed for maximum sea pressure resistance, isn't designed for optimum speed and maneuverability underwater.
The superstructure, built over the pressure hull, streamlines the boat and compensates for this, making modern boats extremely fast and maneuverable underwater.
The best analogy is a thermos bottle, which has an outer shell (the superstructure) that protects and insulates the inner thermal bottle (the pressure hull).
The Russians are known to use a double-layered superstructure on their larger boats
Ballast Tanks -
A ballast tank is a tank or compartment either at the bottom of a ship or on the sides, which is filled with liquids for stability of the ship.
Ballast tanks are located between the inner and outer hull of a submarine. When a submarine needs to submerge it fills these tanks with sea water. This changes the buoyancy of the submarine. Special ballast tanks, located forward and aft, are known as “trim tanks.” They are filled with air or water allowing the bow or stern of the submarine to rise and sink.
Engines -
The earliest known submarines were propelled by human foot petals. According to New World Encyclopedia, “The first mechanically driven submarine was the 1863 French Plongeur, which used compressed air.” Later came battery power for running submerged and diesel power for running on the surface and charging it’s batteries. This type of submarine is known as diesel electric. The diesel motors do not drive the propellers but power electric motors that do. Submarines built since the 1950′s have nuclear power. Nuclearpowered submarines, from World Nuclear Association, can stay submerged for extremely long periods of time. Everything the crew needs is provided by the nuclear reactor. Air fresh water and electricity.
Conning Tower -
Also known as the “sail” or “tower,” this is the control center of the submarine. A periscope is located in the conning tower so the submarine can remain completely submerged and still visually see what is on the surface. All of the submarine’s operating systems are controlled and monitored from the conning tower. Hydroplanes -
Located on the bow and stern of a submarine are the hydroplanes.
These work like the flaps on an airplane. As the submarine is propelled through the water the hydroplanes can be adjusted to make the submarine dive or surface.
The vertical fin is the rudder, which turns the submarine right or left. Weapons -
Modern submarines carry with them a wide range of weapons, from Shima Demon.
They have conventional torpedo's , missiles, anti ship missiles, mines, cruise missiles and nuclear missiles.
The power of destruction empowered in a nuclear submarine is hard to believe. Navigation -
Submarines cannot visually see where they are going while submerged. They depend upon a lot of electronic equipment to accomplish this task.
Submarines use GPS satellites, as in GPS 101 by Richard Lewis, SONAR, inertial guidance. GPS satellites can pin point a submarine’s exact location anywhere in the world.
SONAR, from How Stuff Works, uses sound pulses sent out into the surrounding sea and listens for echoes reflecting back indicating any obstructions. The inertial guidance system uses gyroscopes that can tell direction and distance traveled but only for about 10 days. Life Support -
In the past, submarines had to surface regularly to renew their air supply and charge their batteries. Today’s nuclear submarines convert sea water, by electrolysis, to make oxygen and scrub carbon dioxide from stale air.
They also make fresh water from sea water using electricity. Nuclear submarines have large stores of food supplies on board so they can remain submerged for several months at a time.