Each game can vary in the number of ships employed but a common practice is to have 5 ships of differing size (2 to 5) squares. An aircraft carrier is 5 squares long, a battleship is 4 squares long, both a submarine and a destroyer are three squares long and a patrol boat is two squares long. Each player must secretly place their ships on a grid of ten columns by ten rows. These represent the location of the ships on a battlefield. Each player will also be in possession of a second grid of the same size. Where the first grid is their own ships, the second one (which is blank at the beginning of the game) is a mirror of their opponent’s battlefield.