A naval unit, as its name implies, is a unit that fights on the water. They are the most numerous type of unit after ground units. All naval units can only move over water, and most can traverse both shallow and deep seas (except Galleys, which can only traverse shallow seas). All naval units other than Submarines can carry ground units as passengers, and can transport them to islands or other continents. Naval units can defend against air units, but cannot attack them.