Most submarines use sonar to track other vessels

When were submarines first used in war?

By early 18th century , many inventors had made designs of vessels that could travel on the surface of water as well as under it. The American revolution (1775-1783) was the first war that witnessed military deployment of such boats.

The `Turtle', also known as the ' American Turtle', was the world's first submersible vessel designed to affix explosives under British warships -but its attempts were unsuccessful. Later, submarines were also used during the American civil war (1861-1865).

Submarines equipped with torpedoes became a major factor during the two world wars. About 40 countries operate submarines at present.

How does it submerge?

One of the most important features of a submarine's design is the bal last tanks. These tanks can be filled with water or air depending on whether the vessel wants to travel underwater or float on the surface.The tanks are filled with air when the submarine is on the surface.

To submerge, the air is released and the tanks are filled with sea water, which makes the vessel heavier.Submarines maintain a stock of compressed air while travelling underwater. This air is used for life support and filling the ballast tanks.

How is a submarine propelled?

Most of today's diesel submarines work like hybrid vehicles. A typical diesel submarine has two diesel engines. One is used to propel the vehicle when it is on the surface andthe other to charge its batteries. These vehicles can only go underwater after fully charging their batteries.

After going underwater, they are propelled by batterypowered electric motors. Because of battery-powered propulsion, the diesel submarine can stay underwater for a limited period. A nuclear-powered submarine is not based on a combustion en gine. Unlike diesel subs, a nuclear sub doesn't need air to burn fuel and hence can remain underwater for much longer periods.

How is underwater navigation performed?

Typically , submarines don't have windows and hence the crew cannot see outside. When a submarine is near the surface, it uses a periscope for a view of the outside. Most submarines travel much deeper than periscope depth and navigation is done with the help of computers. Like any other conventional ship, a submarine navigator is also dependent on regular ocean navigation charts. The movement of the vessel is strictly monitored by computers. These vessels are also equipped with antennae that can connect to the GPS when they are near the surface.Submarines use Sonar (Sound Navigation and Ranging) to detect target ships. While using active sonar, the submarine transmits a sound pulse and calculates the time it takes to reach the target and be reflected back.Passive Sonar listens for sounds coming from other vessels.

How is the submarine's environment controlled to support life?

To have a healthy environment for humans, a submarine must maintain Earth-like air quality , supply fresh water and maintain a suitable temperature. Most submarines are equipped with oxygen generators and water purifiers. These use sea water to generate oxygen as well as produce fresh water. Carbon dioxide and moisture are periodically removed to keep the environment healthy .