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This page is written by the game's inventor, David Short.

Cannons and Crabs

By David Short


Here is my entry for the contest to devise a chess variant on exactly 42 squares.

Board and Setup

The Pieces

Unless otherwise noted, all pieces capture the same way that they move.

KING (K) = moves as a standard chess King, one square in any direction. The object of this game is to checkmate the enemy king.

ROOK (R) = moves as a standard chess Rook, any number of squares horizontally or vertically.

KNIGHT (N) = moves as a standard chess Knight, in an "L"-shaped move, 1-2 or 2-1.

PAWN (P) = moves and captures like a standard chess Pawn, except that it may only move one square on each move, even its first move.

CANNON (C) = may move one or two squares in any direction and may also jump pieces of either color, except that a Cannon may not jump over an intervening piece in order to attack a King. The jumped pieces are unaffected. (A cannon is very similar to the Champion from Omega Chess, except that a cannon MAY move EXACTLY one square diagonally, whereas a champion may not, and a Champion may threaten a King even with an intervening piece.)

CRAB (WCR for white crab, BCR for black crab) = captures like a standard chess pawn (one square diagonally forwards) but in addition to being able to move one square forwards like a standard chess pawn, may also move one square forwards diagonally in either direction on any move.

(In the above diagram a black dot indicates a square to which either a capturing or non-capturing move may be made, and a green dot a square to which only a non-capturing move may be made.)

Neither crabs nor pawns may move backwards. There is no en-passant rule in this game.

Stalemate is a draw. Draw by 50-move rule also applies (no captures or pawn or crab moves for 50 consecutive moves by both sides).

Both crabs and pawns may promote upon reaching the last rank. However they are limited to promoting to only two different possible pieces, the Marshall (M) which combines the powers of a rook and knight, or Cardinal (WCD for white cardinal, BCD for black cardinal) which combines the powers of a bishop and knight.

CASTLING: The king may castle with either rook by moving two squares towards the rook and the rook "jumps" over to the other side. The standard prohibitions against castling are in place: the intervening squares are unoccupied, that neither the king nor rook have previously moved, that the king isn't moving on to or over a square controlled by an enemy piece, and the king is not castling while in check. So when castling with the A-file rook, the king would move to b1/b6 and the rook would move to c1/c6, and when castling with the g-file rook, the king would move to f1/f6 and the rook would move e1/e6.


After some initial play-testing by this game's creator, it has been discovered that the original Cannons, which could offer check even when two squares away and blocked, were too strong. In order to offset this somewhat, the following rule change has been implimented: A check from an enemy cannon two squares away from one's own king may be interposed by any piece. The enemy cannon may NOT then "jump" over that piece and "capture" the king. Checks from cannons 2 squares away may be interposed.

Zillions of Games

There is an implementation of Cannons and Crabs for Zillions of games. You can download it here:

The latest version is 1.3 (check the ZRF's history entry) -- earlier entries had the old Cannon move. A variant on a 7x7 board is included.

Written by David Short. HTML conversion by Peter Aronson.
WWW page created: June 20th, 2001.
Page Last edited: October 1st, 2001.