What is Kriegspiel?

Kriegspiel is a chess variant invented by Henry Michael Temple in 1899 and based upon the original Kriegsspiel developed by Georg von Reiswitz in 1812. In this game, each player can only see their own pieces, and must deduce the opponent's positions and moves based on the referee's valid move confirmations and captured piece announcements. The game necessitates the use of three chess boards - one for each player and one for the referee. The term Kriegspiel literally translates to war game in German.