Underwater Submarines sink by taking in ocean water into large tanks. This weighs them down, allowing them to sink. They take in as much as they need to go as low as they want to. When they want to return, they pump out the water by pumping pressurized air into the tanks. This forces the water out, turning the tanks into floaties and boosting them back to the surface.
How They Make Oxygen
They have specialized machines that make oxygen from ocean water. They use electrolysis, which means electricity breaks apart H20 molecules to get oxygen.
Submarines Move Forward Using Propulsion
Submarines propel themselves forward through the water using propellers or jets that shoot out water. Diesel engines or even nuclear reactors can fuel these. They use a rudder, just like a ship, to turn.
