A submarine has several large tanks inside that are filled with air when the ship is floating on the surface of the water. It is the air, which is lighter than water, that keeps the submarine afloat, just like any other type of ship.
However, these deposits are different from those of vessels floating on the surface; in submarine deposits there are gates at the top and bottom. These gates, called valves, can be opened to allow seawater or air to enter.
When the lower valve opens, seawater fills each tank, and the air that was in the tank is forced out through the other valve at the top. Already with the interior filled with water, it increases the weight of the submarine and causes the ship to dive.
In order to bring the submarine back to the surface once again, pumps are used to draw the water out of the tanks, and air is blown back in. This new air is the compressed air that has been stored in large metal containers, which is injected into the tanks at high pressure. Again with the tanks full of air, the submarine is raised.
A submarine can dive to a depth of 30 meters in less than a minute. Some of the research submarines are designed to dive to depths of 1,500 meters. These submarines have thick steel hulls to withstand the immense water pressure at that depth.
History was made in 1960 when the submarine Triton traveled around the world in an underwater voyage of 66,500 kilometers in 84 days.
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