Double Diamond

Double Diamond is a diagonal chess variant played on a 9x9 board from which four squares at each of two corners have been removed, leaving 72 squares in all (see Figure 1). Each player has the usual complement of pieces, plus a marshall (which moves like either a rook or a knight), and nine pawns. The standard chess rules apply, with only a few differences.

Figure 1. The opening layout in Double Diamond.

          +---+---+---+---+---+---+---+
9         |   |   |*r*|*n*|*b*|*m*|*k*|
          +---+---+---+---+---+---+---+
8         |   |*p*|*p*|*p*|*p*|*p*|*q*|
  +---+---+---+---+---+---+---+---+---+
7 |   |   |   |   |   |   |   |*p*|*b*|
  +---+---+---+---+---+---+---+---+---+
6 |   | P |   |   |   |   |   |*p*|*n*|
  +---+---+---+---+---+---+---+---+---+
5 | R | P |   |   |   |   |   |*p*|*r*|
  +---+---+---+---+---+---+---+---+---+
4 | N | P |   |   |   |   |   |*p*|   |
  +---+---+---+---+---+---+---+---+---+
3 | B | P |   |   |   |   |   |   |   |
  +---+---+---+---+---+---+---+---+---+
2 | M | P | P | P | P | P |   |
  +---+---+---+---+---+---+---+
1 | K | Q | B | N | R |   |   |
  +---+---+---+---+---+---+---+
    a   b   c   d   e   f   g   h   i

Pawns advance by moving one square at a time diagonally rather than orthogonally. They advance toward the enemy position, the white pawns moving upward and to the right in Figure 1, the black pawns downward and to the left. Pawns capture by moving one square at a 45-degree angle to their direction of advance. Their capture move is orthogonal rather than diagonal, in either of the two directions that approach the opposing side. Note that these are not Berolina pawns: the latter have a choice of two diagonal non-capturing moves and only one square on which they can capture. Double Diamond pawns have only one possible direction of movement, and two capture moves, just like orthochess pawns.

DD pawns can move two squares on their initial move, and en passant capture is allowed. Pawns are promoted when they reach any of the squares on the L-shaped row/column portions of which are occupied by the enemy pieces at the beginning of the game. Note that in the opening setup, all of each player's pawns except the kings' pawns protect one another.

Figure 2. A Double Diamond pawn advances diagonally and captures orthogonally. The white pawn on d5 can capture the black bishop, but it can't make a non-capturing move, because its path is blocked by the black pawn on e6. If the black pawn has just advanced two squares from its starting position on g8 (marked 'o' in the ASCII diagram), it can be captured en passant by the white pawn on f6, whose capturing move takes it to f7, the square the black pawn crossed during its two-square move. The white pawns will promote when they reach any of the squares marked 'x'.

          +---+---+---+---+---+---+---+
9         | x | x | x | x | x | x | x |
          +---+---+---+---+---+---+---+
8         |   |   |   |   | o |   | x |
  +---+---+---+---+---+---+---+---+---+
7 |   |   |   |   |   |   |   |   | x |
  +---+---+---+---+---+---+---+---+---+
6 |   |   |   |*b*|*p*| P |   |   | x |
  +---+---+---+---+---+---+---+---+---+
5 |   |   |   | P |   |   |   |   | x |
  +---+---+---+---+---+---+---+---+---+
4 |   |   |   |   |   |   |   |   | x |
  +---+---+---+---+---+---+---+---+---+
3 |   |   |   |   |   |   |   |   | x |
  +---+---+---+---+---+---+---+---+---+
2 |   |   |   |   |   |   |   |
  +---+---+---+---+---+---+---+
1 |   |   |   |   |   |   |   |
  +---+---+---+---+---+---+---+
    a   b   c   d   e   f   g   h   i

In the opening setup, all of the bishops are on squares of the same color. In order to balance the game, a special rule is needed: At any time any bishop can make a non-capturing move of exactly one square vertically or horizontally. This move may also help compensate for the fact that the pawns' movement tends to block the bishops' development.

Castling can be done in either direction by moving the king two squares toward the rook, and moving the rook to the square immediately past the king.

Strategy note. A good opening ploy may be to move a pawn (for example, e2-f3 by white) so as to free a rook to command the center.

If you'd care to play a game of Double Diamond by email, please feel free to wander over to the Contributors page, where the author's email address is located.