From submarines in Finding Out About Everyday Things
The submarine has some tanks. To go under water, the tanks fill up with water, which makes the submarine heavy, so it sinks down. In order to stay the same depth, the water moves from tank to tank. And to make it go up to the surface, the water goes out of the tanks and they fill up with air and the submarine goes up to the surface. And then a boat with a crane on it lifts it out of the water and puts it in place on the boat.
A submersible is a kind of submarine. It is made to go down in the ocean where the pressure is really strong. There are divers that go through a little door in the bottom of the submarine into the water. There is a telephone line that goes from the submarine and attaches to the diver’s suit. That way he can talk to the guys in the submarine.
There is something I didn’t know about submersibles –they are made to remove cables and things from the sea beds. There are two robotic arms that grab the tubes and things and hold them.
There is a propeller in the back — actually 1, 2, or 3 — and the propellers spin to push the submarine through the water.