Warmatrix

Submarines are ships that can travel under water. In war, they act as stealth attackers.
To breathe under water, diving bells have been used since ancient times. The first military submarine was the Turtle, built as early as 1775 CE by the American David Bushnell. It was hand-powered and used screws for propulsion. Though quite revolutionary in concept, it proved unable to sink an enemy ship. For decades submarine technology did not progress significantly. During the 19th century CE inventors started to build progressively better machines, using compressed air, steam power and later gasoline and kerosine for propulsion. The real breakthrough was in the 1880's CE with the introduction of the electric battery, though it took about two decades to take hold. Early 20th century submarines used diesel power on the surface and batteries when submerged.
Further improvements were necessary before the submarine became more than a curiosity, but these came rapidly: torpedoes as early as 1866 CE; periscopes in 1888 CE; diesel electric propulsion around the turn of the century; ASDIC around 1920 CE; sonar from the 1930's CE onward. Submarines seldom use active sonar or radar; instead they rely on passive systems that do not betray their presence to other listeners. Despite all the improvements in propulsion, weaponry and sensory systems, life aboard a submarine was and still is taxing for its crews. They work and live in cramped quarters for prolonged periods.
Submarines were and still are used as stealthy spies, messengers, personnel carriers, supply ships or mine layers. In combat their traditional role is to sneak up on enemy ships and sink them using torpedoes. Sometimes they surface and engage ships using a cannon, usually to save torpedoes, of which they can carry a limited number. Submarines seldom attack other submarines, because they evade each other easily.
In World War I submarines made their first notable contribution to war, with German U-boats sinking more than 5,000 enemy ships. Many senior naval officers had ignored them until that point, yet were forced to rethink the value of their large but expensive battleships. The German strategy was repeated in World War II, where U-boats, both alone and hunting in 'wolfpacks', nearly strangled Britain's strategic supply lines, until countermeasures were stepped up. A combination of sailing in convoys escorted by warships, better detection equipment, depth charges and attacks from anti-submarine aircraft contained the threat. Submarines played an important part in the Pacific theater too, on both the Japanese and American side.
A typical World War II submarine, the German Type VII, could reach top speeds of 33 kilometers per hour on the surface and 14 submerged, to maximum depth of 230 meters. It carried 14 torpedoes and enough fuel to sail for about 90 days.
After World War II submarines gained a new role, as strategic missile launching platforms. The was made possible by nuclear propulsion, giving rise to the new class of nuclear submarines.