Submarines: History - How They Work - Introduction

To function underwater, submarines are built a bit differently than surface ships that float on the water's surface. In order to travel underwater, submarines must function in agreement with some key laws of nature, including Archimedes' Principle and Boyles' Law.

Submarines are completely enclosed vessels with cylindrical shapes, narrowed ends and two hulls: the inner hull and the outer hull. The inner hull protects the crew from the immense water pressure of the ocean depths and insulates the sub from the freezing temperatures. This hull is called the pressure hull. The outer hull shapes the submarine's body. The ballast tanks, which control the sub's buoyancy, are located between the inner and outer hulls.

To stay in control and stable, a submerged submarine must maintain a condition called trim. This means its weight must be perfectly balanced throughout the whole ship. It cannot be too light or too heavy aft or too light or too heavy forward. The submarine's crew must continually work to keep the submarine trim because burning fuel and using supplies affect the sub's distribution. Tanks called trim tanks, one forward (front half of boat) and one aft (back half of boat), help keep trim by allowing water to be added or expelled from them as needed.

Once the submarine is underwater, it has two controls used for steering. The rudder controls side-to-side turning, or yaw, and diving planes, control the sub's rise and descent, or pitch. There are two sets of diving planes, the sail planes, which are located on the sail, and the stern planes, which are located at the stern (back) of the boat with the rudder and propeller. Some submarines, including the new Virginia class, make use of bow planes (diving planes located at the bow, or front of the boat) rather than sail planes.

As you will notice on the above diagram of a submarine, it has a tall sail that rises out of the submarine's hull. Inside this fin-shaped sail is the conning tower ("conn" means to direct the steering of a vessel). The periscope and radio and radar antennas are usually extended through the conning tower. In the past, many of the controls used to operate submarine while on the surface were located here.

A periscope enables a submarine to see what is happening on the surface while remaining underwater. Only the end of the periscope must break the water. The periscope is made with mirrors and lenses that reflect and bend images down a long tube to the eye of a Sailor. A submarine operating at periscope depth is completely submerged, but at a depth where the periscope is still able to break the surface.

As advances in technology are made, the look and operation of submarines change. A major breakthrough in the new Virginia-class submarines is the use of Photonics Masts, eliminating the need for a conventional periscope. Instead of a Sailor on a Virginia-class boat using a series of mirrors and lens to view above the surface, several high-resolution, color cameras will send visual images to large screen displays in the ship's control room via fiber optics.