A submarine is a vessel, or ship, that can go underwater. Submarines are called subs for short. Military forces and scientists use submarines to travel deep under the ocean.
Armies and navies around the world, usually of powerful countries, use submarines to patrol ocean waters and to attack enemy ships during wartime.
Military submarines
Military submarines are usually very large. They may carry more than 100 people. They also carry such weapons as missiles and torpedoes. Submarines used for scientific purposes are usually smaller that military-grade ones. 
Such submarines may have metallic arms that extend from the body, as well as cameras, to help researchers find new information about life.
Ballast tanks
A submarine has huge tanks, called ballast tanks, that allow it to dive and to surface. The tanks fill with water to give the submarine the weight it needs to sink. When the submarine is ready to surface, the ballast tanks release the water and get filled with air. This lightens the vessel enough for it to float.
For power, submarines use engines, batteries, nuclear power sources, or a combination of these. Propellers push submarines through the water.
Complex equipment
A submarine’s crew uses complex equipment to find the way through deep, dark oceans. To find enemy submarines or other targets, both military and scientific submarines may use sonar. Sonar equipment locates objects by picking up sound waves. Other onboard equipment provides clean air and fresh water to the crew.
A Dutch inventor named Cornelis Drebbel built the first working submarine in 1620. It was a leather-covered rowboat that could reach a depth of 15 feet (4.5 meters).
The U.S. inventor David Bushnell built a submarine that he ran in 1776 during the American Revolution. In 1800 the famous U.S. inventor Robert Fulton built the Nautilus. This was a small submarine that could attach explosives to ships.
Other inventors experimented with gas-, steam-, and battery-powered submarines. By the early 1900s submarines had both a diesel engine (a type of internal-combustion engine) and battery-powered electric motors. The diesel engine ran the submarine on the surface. The electric motors ran it underwater.
Militaries used these diesel-electric submarines in World War I (1914–18) and World War II (1939–45).
USS Nautilus
The U.S. Navy introduced the first nuclear-powered submarine in 1954.
It was named the USS Nautilus. She is also known for being the first submarine, nuclear-powered or diesel-powered, to complete a submerged transit of the North Pole on 3 August 1958.
H.L. Hunley
It was the first submarine in history to successfully sink an enemy ship. Made out of 40 feet of bulletproof iron, the H.L. Hunley was a Confederate submarine with a crew of eight. But despite its claim to fame, it was a dangerous vessel to be inside.
In a career of just eight months during the Civil War, between July 1863 and February 1864, the sub sank three times, killing nearly 30 men—including its inventor. (It was recovered twice.) Its final sinking, shortly after it plunged a live torpedo into the hull of the Union warship USS Housatonic, has long mystified maritime and military historians.
Dinara Hettiarachchi
Grade 8
Ananda College
Colombo