This has got to be one of the most fascinating things I've seen. I, personally have never seen anything like it, but the table is self-leveling. Meaning, it is Gyrocscopic - the table will remain level regardless of how rough the seas get. It is mechanically engineered to move with the ship.
YouTube: As the ship moves the pool table adjusts so that the billiard balls don't move at all, even in rough weather. If you look closely you can see that the balls remain still as the table moves, enabling you to play in almost any conditions..