Kriegspiel

In Kriegspiel, each player knows their own pieces but cannot see the opponent's complete position. A referee maintains the true board and controls what information each participant receives. Traditional physical play uses private player boards and a third concealed board for the referee; digital software performs the same role automatically.

How a move is made

1. The player proposes a move from the information currently available.
2. The referee checks the complete position. If the attempt is illegal, the player is told and must try again.
3. When a legal move is accepted, the referee updates the true position and announces only the facts permitted by that rule set.

Under the English Gambit Club rules, a capture announcement gives the square where it occurred but normally does not identify the capturing or captured piece. If the king is in check, meaning that it is under attack, the referee also announces the general line: file, a vertical column; rank, a horizontal row; long diagonal; short diagonal; or knight. A player may ask whether any pawn has a capture under specified conditions.

Illegal attempts are not merely procedural mistakes. They can reveal information. If a rook tries to cross a line and the referee rejects the move, the player learns that some obstruction or restriction exists without learning its exact cause. Choosing what to test is part of the strategy.

The objective remains checkmate, when the king is attacked and no legal reply exists. The referee, who sees the complete position, declares the result. Capturing the king is not the normal winning rule.

Kriegspiel has several published rule sets, including English, Berkeley, Cincinnati, and Wild 16. They differ in details such as who hears an illegal attempt, how captures are announced, and what pawn information is provided. Players must agree on the rule set before starting.

It differs from Fog of War chess in how information is delivered. Fog of War displays a partial region based on piece reach; Kriegspiel relies on attempted moves and discrete referee messages.