Submarine

World War II submarine "USS Sea Owl"

A submarine is a vessel that goes under water. Submarines are often war vessels, but some are used for scientific or business purposes. People with a lot of money can even buy their own small submarine to explore under the sea and look at fish. A submarine is always called a boat, not a ship.

In early times, submarines were often powered by hand, as boat engines had not yet been invented. They were almost always designed for war purposes, and would attempt to sink enemy ships by crude methods like drilling screws into their wooden hulls. Some attempted to blow ships up, but this would often destroy the submarine as well.

Later, during the first and second world wars, more practical submarines were developed, mostly by Germany. They were powered by a diesel-electric system. A diesel motor would be used to turn a generator which would charge a large number of batteries while the submarine was above the water. This power was then used to power the submarine when it went underwater. These submarines were dangerous for enemies and hard to see while under water but it was easy to attack them when they were above the water and recharging. They were only used to attack ships.

Most modern military submarines are powered by nuclear reactors. These submarines often have a system which can get air from the surrounding seawater as well, this combination allows them to stay under water until their food runs out. Their most important functions are attacking ships or launching rockets like cruise missiles, or nuclear missiles. There are two kinds of these subs: attack subs, which are small and fast and attack other subs and surface ships with a special kind of underwater bomb called a torpedo, and missiles subs, which are larger and slower, and designed mainly to shoot missiles at far-away targets on land. Missile subs are usually big enough that they can transport commandos and launch them safely from their torpedo tubes.