The game is played on four square grids, two for each player. The grids are typically square — often 10×10 — and the individual squares in the grid are identified by letter and number. On one grid the player arranges his own ships and records the shots by the opponent. On the other grid, the player records his own shots.
Before play begins, each player arranges a number of ships secretly on the grid for that player. Each ship occupies a number of consecutive squares on the grid, arranged either horizontally or vertically. The number of squares for each ship is determined by the type of the ship. The ships cannot overlap (i.e., at most one ship can occupy any given square in the grid). The types and numbers of ships allowed are the same for each player. These may vary depending on the rules.
After the ships have been positioned, the game proceeds in a series of rounds. In each round, each player has a turn. During a turn, the player announces a list of target squares in the opponents' grid which are to be shot at. If a ship occupies one of the squares, then it takes a hit. When all of the squares of a ship have been hit, the ship is sunk. After the target list has been given, the opponent then announces which of his ships have been hit. If at the end of a round all of one player's ships have been sunk, the game ends and the other player wins.
The number of target squares that a player may shoot at in a given turn is determined by the condition of the players' own ships at the beginning of the round. Each player has as many shots as he or she has vessels afloat in each turn. Thus each time a player's ship is entirely destroyed, that player has one fewer shot on all subsequent turns.