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
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
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.