Los Alamos chess is a chess variant played on a 6×6 board without bishops and was the first chess-like game played by a computer program on the MANIAC I computer in 1956. The limited computer capacity at the time required the reduction of the board size and number of pieces. The program, mainly a minimax tree search, looked four plies ahead and computed scores based on material and mobility. In an interesting twist, the computer won against a human player in a chess-like game for the first time, marking a significant advancement in technology.
https://en.wikipedia.org/wiki/Los_Alamos_chess