6x6-board Chess © 1956 Los Alamos Atomic Energy Laboratory.
An early Chess game was developed on the MANIAC I computer in Los Alamos.
The program had around 600 instructions and has an average playing time of about 12 minutes per move.
Unlike earlier attempts at chess games this game did allow players to run a full game of chess, but it used a simplified board with only 6x6 squares. It implemented Claude Shannon's system for determining a move (as implemented in the Electric Chess Automaton in 1949). The game calculated all possible moves over two levels of the decision tree and then using static factors and minimaxing to determine the best move. The computer could do roughly 11,000 operations per second and calculating a turn took 12 minutes. It is known to have played three games. It's reported to have roughly equal skill to player with twenty matches of experience.
Game Playing with Computers, Donald D. Spencer (1968) Page 15