"Hehe, I guess my next project will be a magic submarine, a small one will be fine," Billy thought. "Not like I need an airplane, or something faster than the magic aircraft… Anyway, how does pressurized air in a submarine work again?"
In submarine technology, a vent is a valve fitted to the top of a submarine's ballast tank to let air escape from the top of the ballast tank and be replaced by water entering through the openings called "flood ports" or "floods" at the bottom of the tank. In earlier times, the openings at the bottom of the ballast tank were fitted with valves.
