Los Alamos

The first chess variant ever played by a computer (1956, MANIAC I at Los Alamos National Laboratory). A 6×6 board with no Bishops and no castling.

Los Alamos Chess — starting position (6×6)

Setup

Board: 6×6 (six files, six ranks).

Setup (FEN): rnqknr/pppppp/6/6/PPPPPP/RNQKNR

Each side: Rook, Knight, Queen, King, Knight, Rook (+ 6 pawns). No Bishops.

Rules

Standard chess movement for all pieces (Rooks, Knights, Queen, King, Pawns).
No Bishops exist in this variant.
No castling.
Pawns move one square forward only (no double-step from starting rank).
No en passant (since there’s no double-step).
Pawns promote on the far rank to Queen, Rook, or Knight (no Bishop promotion since Bishops don’t exist).

Win Condition

Checkmate or stalemate the opponent (stalemate is a loss in Los Alamos rules).

Strategy

Without Bishops, there are no long-range diagonal attackers. Knights become relatively more powerful since the board is smaller (fewer moves to cross). The Queen is overwhelmingly strong on a 6×6 board — trade it only for the opposing Queen. Games are short and tactical. The smaller board means Kings have fewer escape squares, making endgame mating patterns easier.

Attribution

Paul Stein and Mark Wells, Los Alamos National Laboratory, 1956. Public domain.