It's an old game Battleship. You have a field where you want to place the ships of its fleet. The enemy is exactly the same field, the same number of ships and it also hides them from you. When both sides are all the ships apart, you in turn start to bombard enemy waters, hoping to get lucky. If you hit the ship, the cell will turn, in which case it must finish. The winner is the side that the first time to sink the navy opponent. Ships are very different, they are distinguished by their length, which is measured in the number of cells that covers the ship.