"Yeah, that's a lot about Submarines, but not what I wanted to know!"

This is how a submarine can dive and then surface.

Just like any boat, a submarine uses what is sometimes referred to as Archimedes' Principle, which is

"a body that is submerged into a fluid, loses exactly the same amount of weight, as the weight of the displaced fluid".

This means that a big heavy hollow boat loses a lot of weight when it is in the sea. What a submarine can do is change the amount of water it displaces. This is done by having a ballast tank which can be filled by water or air. Pressurized air is contained in another tank in the submarine.

  • Fill the ballast tank with water - the submarine will sink.
  • Fill the ballast tank with air - the submarine will rise.
                         |   |
                         | | |
      Air tank        |        |
            |         |        |
            |         |        |
   ---------|---------|        |------------------
  /  |ooooooooooooooo|                            \
 /    ---------------                              \
(                                                   )
 \    _______________                              /
  \  |wwwwwwwwwwwwwww|                            /
            |     |       
            |     -----------Ballast Tank

Simple as that!