Tri-Dimensional Chess

Overview

The chess played on the Enterprise: three main boards stacked and offset, with four small attack boards that can move during the game.

Where the rules come from. The show never explained how the game is played, and we know of no rules published by its rights holders. Players use rules written by fans. Andrew Bartmess's Federation Standard Rules are sold as a booklet; we haven't read them. This page follows the Laws of the World Tri Dimensional Chess Federation, a fan body that publishes its full rules free. Other rule sets differ in places, so agree which you're using.

1. The board

• Three main levels, each 4×4, one above another. Each is offset from the next by exactly half its width, so half its squares sit directly over or under half the squares of the next level.
• Seen from above, the three levels make a chequered area eight ranks long and four files wide.
• Four attack boards, each 2×2, sit over the outside corners of the lowest and highest levels. They can be moved to the corners of any level later in the game.

Colours line up: a square directly above or below another has the same colour.

2. Setup

Each player has the usual 16 pieces: king, queen, two bishops, two knights, two rooks and eight pawns. Each player's pieces go on the two outermost ranks at their own end:

• On the main level: a bishop at each end of the back row with the king and queen between them, the queen on her own colour, and four pawns in front.
• On each attack board at that end: a rook on the outer back corner, a knight beside it, and two pawns in front.

The Laws don't say which colour moves first.

3. Moving the pieces

Seen from above, the pieces move as in ordinary chess: the king one square any way, the queen, rooks and bishops in straight lines until blocked, and the knight one square straight then one diagonally, jumping over anything in the way. Pawns move one square forward, two on their first move, capture diagonally forward, and can take en passant.

Changing level

A square counts as the same position as the squares directly above and below it. A piece follows its normal path across the board and, at any point on that path, including the start and the end, may step straight up or down to an empty square and carry on. A piece can also run off the edge of one board if there's an empty square directly above or below where it would have gone.

Moving an attack board

As your whole move, you can move an attack board to an adjacent corner on the same level, or to a corner on an adjacent level no more than two squares away, and may turn it round as you go. The Laws allow this when only one square of the board is occupied, by one of your own pieces other than the king. They don't say whether an empty board may move.

A board move may never carry a pawn backwards. And you may not move an attack board off your own back corner while an opponent's pawn stands on that corner, because that would promote the pawn at once.

Castling

Two forms, both needing the king, the rook and the attack board involved to be unmoved, the squares between cleared, and the king not in check before or after:

• King's side: the king takes the rook's place on the outer back corner of its attack board, and the rook moves to the king's corner of the main level.
• Queen's side: the king goes to the inner back corner of the queen's attack board, and the queen's rook goes to the queen's starting square.

4. Promotion

A pawn reaching the back rank at the far end becomes any piece except a king. If an attack board sits at that end and continues the pawn's file, it must reach the back rank of that attack board instead.

5. Winning

Checkmate. You may never leave or put your own king in check. A player with no legal move who isn't in check is stalemated, and the game is a draw. The players can also agree a draw when neither can win.

Commonly argued

• There are no official Star Trek rules. Every rule set is fan-written.
• A piece may change level at any point on its path, including where it starts and where it finishes.
• Attack boards move, and moving one uses your whole turn.
• An attack board can't carry a pawn backwards.
• Stalemate is a draw, as in ordinary chess.