XP 139 Submarines

Everyone knows what a submarine is, but only a few people have ever dived down in a sub before. Every submarine has multiple ballast tanks that can be filled with water. Based on how much water is in the tank, the submarine can submerge faster. By emptying the tanks and filling them using compressed air, submarines can resurface. There are also two types of ballast tanks, the interior ones and the exterior ones. The exterior tanks are the ones that are used to make the submarine dive and the interior ones are then used to balance the submarine underwater.
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Some submarines are even able to stay underwater for a months at a time. They can also use a variety of energy sources including nuclear energy, batteries, gas, steam, and even human power. Nuclear powered submarines are able to move faster and stay underwater longer.

Submarines are used by the military to attack enemy ships and to protect their own, mainly the aircraft carriers. They are also great at providing surveillance and detecting incoming attacks.