World War II submarine "USS Sea Owl"
A **submarine** (or **sub**) is a vessel that goes underwater. Most large submarines are war vessels. Some small ones are used for scientific or business purposes. These are often called "submersibles" and cannot go far or stay long away from base. Some people buy their own to explore under the sea. A submarine is a boat, not a ship.

History
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Early submarines were often powered by hand. This is because boat engines had not been invented yet. They were almost always made for war. Submarines would try to sink enemy ships by crude methods. These included drilling screws into their wooden hulls. Some tried to blow up a ship. This often destroyed the submarine, too. At the end of the 19th century, the Whitehead torpedo and electrical systems allowed much better submarines.

These better submarines were much used during the First and Second World Wars. Many of these better submarines were created by Germany, called U-boats. The submarines were powered by a diesel-electric system. A diesel motor would be used to turn a generator. The generator would charge a large battery while the submarine was on the surface. The power in the battery was then used by the submarine when it went underwater. These submarines were dangerous to enemies. They were difficult to see while underwater but it was easy to attack them when they surfaced to recharge. Many modern boats still use this diesel-electric propulsion system.

The First Battle of the Atlantic was the first major battle that was mainly fought between submarines and their enemies. As in later wars, the main jobs of submarines were to enforce a blockade and to sink enemy warships. They usually attacked freighters at night, shooting with their deck guns and then hiding under the water. Sometimes they used their torpedoes, which they could fire while underwater, especially against larger ships and warships. During World War II The US Navy lost around 52 submarines due to combat and non-combat causes. 

After World War II better sonar helped the enemies of submarines to find and destroy them. New subs were more streamlined and had no deck guns because water dragging against the guns made noise underwater and slowed the subs.

Modern submarines
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Most large modern military submarines are powered by nuclear reactors. These submarines often have a system which can get air from the seawater. These two things allow them to stay underwater for long periods of time. Their most important uses are attacking ships or launching missiles. These include cruise missiles and nuclear missiles. There are two main kinds of subs. Attack submarines are small and fast. They attack other subs and surface ships with torpedos. Missile subs are larger and slower. They are built to shoot missiles at far-away targets on land.

Other websites
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* Submarine -Citizendium

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Modern warships |
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| Aircraft carriers | 
* Aircraft carrier
* Escort carrier
* Helicopter carrier
* Submarine aircraft carrier
* Balloon carrier
* Seaplane tender
* Light aircraft carrier
* Amphibious assault ship
* Aircraft cruiser
* Anti-submarine warfare carrier
* Fighter catapult ship
* CAM ship
* Merchant aircraft carrier
* Supercarrier

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| Battleships | 
* Battleship
* Fast battleship
* Coastal defence ship
* Dreadnought
* Pre-dreadnought battleship
* Treaty battleship

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| Cruisers | 
* Cruiser
* Armored cruiser
* Battlecruiser
* Aircraft cruiser
* Protected cruiser
* Unprotected cruiser
* Heavy cruiser
* Light cruiser
* Flight deck cruiser
* Merchant raider

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| Escort | 
* Destroyer
* Guided missile destroyer
* Destroyer escort
* Frigate
* Aviso
* Kaibokan
* Sloop
* Convoy rescue ship

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| Transport | 
* Troopship
* Amphibious warfare ship
* Dock landing ship
* Landing Ship Tank
* Landing Ship Vehicle
* Landing Ship Infantry
* Landing Ship Heavy
* Landing Ship Medium
* Landing Ship Support, Large
* Amphibious transport dock
* Attack transport
* Landing craft

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| Patrol craft | 
* Patrol boat
* Corvette
* Submarine chaser
* Armed boarding steamer
* Ocean boarding vessel
* Armed yacht
* Naval trawler
* Naval drifter
* Gunboat
* Torpedo boat
* Missile boat
* Fast attack craft (MTB, E-boat, MAS, MGB, PT boat)
* Steam Gun Boat
* Harbour Defence Motor Launch
* Coastal Motor Boat
* Q-ship
* Motor Launch

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| Mine warfare | 
* Mine planter
* Minelayer
* Minesweeper
* Destroyer minesweeper
* Minehunter
* Mine-countermeasure vessel
* Danlayer

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| Command and support | 
* Command ship
* Fast combat support ship
* Combat stores ship
* General stores issue ship
* Ammunition ship
* Oiler
* Collier
* Hospital ship
* Auxiliary repair dock
* Crane vessel
* Auxiliary ship
* Destroyer tender
* Submarine tender
* Depot ship
* Dispatch boat
* Net laying ship

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| Submarines | 
* Submarine
* Attack submarine
* Ballistic missile submarine
* Cruise missile submarine
* Midget submarine
* U-boat
* Deep Submergence Vehicle (DSRV)

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| Miscellaneous | 
* Monitor
* Breastwork monitor
* Barracks ship
* Training ship
* Guard ship
* Littoral combat ship

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