Secret Intelligence Chess

For a long time, I did not support any incomplete information games in Game Courier, because it normally makes complete information about the game publicly available. With the idea of enabling it to support incomplete information games like Kriegspiel or Dark Chess, I started working on my own incomplete information game that would rely on the capabilities of Game Courier and its GAME Code programming language to hide certain information from each player. I started by working on Hidden Identity Chess, in which the players could see each other's pieces, but they couldn't see what they were. Since an effective way of hiding pieces was to remove them from the board, I switched to working on a game I called Hidden Danger Chess, in which you could not see where your opponent's pieces were. Finally, I added elements of disinformation into the game and changed its name to Secret Intelligence Chess, as the game involves gathering intelligence on what and where your opponent's pieces are. While this game could be played with a human referee who knows the complete position and can tell players which moves are legal, it is designed for a computer program to run the game, and it will run more smoothly this way.

The biggest difference from most Chess variants is that you cannot see where or what your opponent's pieces are. But you will be informed on which moves have been made and on which legal moves you have, which will give you some intelligence on what pieces your opponent has where. So that you won't know where your opponents pieces are at the start of the game, the setup is randomly chosen. And so that you won't know exactly what pieces your opponent has, some pieces on each side are chosen randomly. Besides the usual Chess pieces and some common fairy pieces, this game also includes some special pieces that have greater intelligence gathering power due to the nature of this game.

At this point, I am satisfied enough with the game to release it, and it is time for beta-testing. Due to the hidden information nature of this game, I cannot test it against a computerized opponent and may only test it against a human opponent. Here is a link to the Game Courier preset:

Secret Intelligence Chess on Game Courier

Setup

This is an unequal armies variant in which each player may end up with a different army. Each side has one King, two Rooks, two Bishops, eight Pawns, and two more pieces that are randomly selected. The program or referee should first pick a random number between 1 and 4. A human may do this with a four-sided die. Do this for each side separately. Depending upon the value, the two pieces are:

1. A Queen and a Centaur
2. A Marshall and a Dragon Horse
3. An Archbishop and a Dragon King
4. A Decoy and a Spy

The setup is determined randomly. This may be done by a computer program or by a human referee who uses dice.

1. Each King is randomly placed on its first two ranks.
2. Each Pawn is randomly placed on its second or third rank.
3. One Bishop is randomly placed on a dark square on the first three ranks
4. One Bishop is randomly placed on a light square on the first three ranks
5. One Rook and one Knight are randomly placed on the left half and the right half on the first three ranks.
6. Every remaining piece is randomly placed on the first three ranks.

Following this procedure, here is an example of what White might see:

And here is how things might look for Black. Since players do not see each other's pieces, the piece White moved is just given a tracking code matching the space it began on.

Pieces

The King, Queen, Rook, Bishop, and Knight all move as they do in Chess, though there is no castling, and all pieces have some extra powers at the beginning of the game. Each piece description is accompanied by an image of a white piece from the Abstract set and a black piece from the Alfaerie set.

The King moves as it does in Chess except that there is no castling. Due to the nature of this game, the King's inability to move into check gives it the ability to detect attacked spaces. Note that one exception to moving into check is that the King may move to a space occupied by the opponent's King. While the game never provides any opportunity for this to happen, it does affect the evaluation of potential moves. If the two Kings share some adjacent spaces, neither can move adjacent to the other, because each King has the ability to capture the other even on an attacked space. Note that this is also true in Chess, and I bring it up now only because some other pieces that may not move to an attacked space will also have this exception.

The Queen moves as it does in Chess. It may cross any number of empty spaces in any orthogonal or diagonal direction, stopping on an empty space or on the first occupied space it reaches.

The Rook moves as it does in Chess. It may cross any number of empty spaces in any orthogonal direction, stopping on an empty space or on the first occupied space it reaches.

The Bishop moves as it does in Chess. It may cross any number of empty spaces in any diagonal direction, stopping on an empty space or on the first occupied space it reaches.

The Knight moves as it does in Chess. It may leap directly to a space located one rank and two files or one file and two ranks away, jumping over anything in between.

The Marshall is a compound of the Rook and Knight, meaning it may move as either piece.

The Archbishop is a compound of the Bishop and Knight, meaning it may move as either piece.

The Centaur is a compound of a Knight and a non-royal King (a.k.a. a Man).

The Dragon Horse can move any number of spaces diagonally like a Bishop or one space in any orthogonal (vertical or horizontal) direction. It is basically a compound of a Bishop and a non-royal King.

The Dragon King can move any number of spaces orthogonally like a Rook or one space diagonally like a Ferz. It is basically a compound of a Rook and a non-royal King.

The Spy is a divergent piece. It normally moves as a Knight, Bishop, or Rook except that it may not move to an attacked space unless it is to stop a check or is to the location of the enemy King. To capture any piece except another Spy, a Spy may not move as that piece would move to capture. So, for example, it cannot attack a King or Decoy from an adjacent space, but it may attack it as a Knight or from a further distance. To give another example, it may not capture a Pawn by moving one space diagonally forward, though it may capture it with a one space move in any other direction, or from further away as a Queen or a Knight. To capture another Spy, it must hop or jump over another piece belonging to the same side. This allows the Spy to move into a position where it is safe from attack while still threatening the opponent's Spy.

The Decoy moves one space in any direction like the King or leaps like a Knight but with some restrictions. The restrictions on its movement come from its purpose in the game, which is to mislead the opponent into thinking it is the King. The first restriction is that it may not move into check except to save its King from check or to capture the enemy King. So, like the King, it has the ability to detect lines of enemy attack. To fool other pieces with this ability, it may not use its Knight leap to capture a King, Decoy, or Spy. Its disguise is not perfect, though. Its Knight leaps might be detected by unmoved pieces that would otherwise be capable of swapping (described in the rules below). But for the most part, its disguise is good enough. Pieces that have already moved will not pick up on its ability to capture with a Knight leap.

Although it may leap as a Knight, using this power will reveal that it is not a King. So you should avoid using it unless it's to your advantage. Even without moving as a Knight, though, just having the power to gives the Decoy more intelligence on its surroundings than the King has.

The Pawn is a Quick Pawn, meaning that it can move two spaces forward anytime, not just on its first move. Whenever it does move two spaces forward, any Pawn that could have captured it on the space it passed over may capture it by en passant by moving to that space. Upon reaching the last rank, it may promote to a Queen, Marshall, Archbishop, Dragon King, Dragon Horse, Centaur, Spy, or Decoy so long as the player does not already have one on the board, or it may promote to a Rook, Bishop, or Knight regardless of whether the player still has any.

Rules

Apart from the differences in army composition and piece setup explained above, Secret Intelligence Chess is played like Chess except as follows:

• You may not see where or what your opponent's pieces are except as follows:

1. You can see the from and to positions of each of your opponent's moves, though you will not be informed on which piece has moved or on what piece a Pawn has promoted to.
2. You can see which pieces have been captured.
3. You will see the positions on the board of the pieces your opponent has already moved, and each will have a tracking ID of the space it began on, but the type of piece it is will remain hidden.
4. You will be told when your move has placed your opponent's King or Decoy in check, though you will not be told whether you have checked the King or just a Decoy.
5. When your opponent's move has placed your opponent's King in check, you will be notified that you are in check.
6. When your King is not in check but your opponent's move has placed your Decoy in check, you will be notified of the check and also told that the check is on your Decoy.
7. When your opponent's Decoy moves into or remains in check, you will not be notified of this at the beginning of your turn, though, per 3. above, you will be notified after your move if the Decoy remains attacked.
8. You may get some indication of where enemy pieces are by looking at your own pieces' legal moves.

• You may not try out a move, then change your mind. While you may take back an illegal move, you should already be fully informed about which moves are legal. This restriction is to prevent you from using aborted moves to uncover what pieces are or to find a winning move.

• Because of the random placement of pieces, there is no castling.

• Two pieces on the same side may swap places under these conditions:

1. Neither piece is the same type as the other.
2. Neither piece has moved under its own power (being the passive piece in a swap does not count).
3. Neither piece is attacked by an enemy piece.
4. One piece can and does move to the other's space by its own powers of movement.

• Upon reaching the last rank, a Pawn may promote to a Rook, Bishop, or Knight or to any more powerful piece the player does not already have on the board.

Notes

Strategy

Gathering Intelligence

It is important to gather intelligence in this game, and this is best done by actively seeking it out. Here are some tips on gathering intelligence:

• Use pieces that cannot move into check to find out where lines of attack may be coming from.
• If you don't have a Spy or Decoy, expose your King enough to detect attacked squares around it.
• Check which unmoved pieces can swap places with each other to find out which of them are attacked.
• Check where pieces may legally move. If a piece with an unlimited diagonal or orthogonal move cannot go all the way to the end of the board, something is in the way.
• Make some moves for the purpose of using a piece to look along ranks, files, and diagonals to see where pieces might be along them.
• Pay attention to the moves a piece has made to rule out some of the possibilities of what it may be.
• Check previous moves to get a better sense of what is where.
• In View mode, check your legal moves for selected previous moves.
• To check whether it is safe to move to a specific space, ask yourself what your opponent has left to capture it, determine what spaces they would need to be on to capture it, and for each of these spaces try to rule out the possibility that it has the piece that could capture your piece. This may involve going over past moves with a specific question in mind, then repeating the process with a different question.

Play Cautiously

If you charge ahead into the enemy camp with a valuable piece, you could quickly lose it. Here are some tips on playing more carefully:

• Determine whether a piece you can capture is at least as valuable as the piece you might use to capture it. You might not know for sure what a piece is ahead of time, but you may be able to tell whether the exchange will be worthwhile.
• Venture forth with your less powerful pieces before exposing your more valuable pieces to danger.

Game Design

Swapping is provided as an option to allow players to correct faults in randomly chosen positions. The restriction that neither piece may be attacked allows for some detection of enemy attacks. The restriction that both pieces must be unmoved prevents the overuse of swapping, and it prevents the use of swapping for rapidly advancing Pawns.

The Decoy and Spy are designed to exploit the rules of this game. While these pieces would not stand out in a perfect information game, they gain extra powers of intelligence gathering in this game. The restriction on the Decoy moving into check allows it to gain intelligence on where enemy attacks are coming from. The divergent powers of the Spy allow it to feel out the long-range positions of pieces without limiting the moves of pieces that cannot move into check.

These pieces were originally lower powered. The Decoy could not move as a Knight, and the Spy could move as a Knight but not as a Nightrider. This is because the randomly selected pairs of pieces originally included a Knight, a Bishop, and a Rook instead of a Centaur, a Dragon Horse, and a Dragon King. Since this change raised the powers of the other three pairs, I increased the power of the Decoy and Spy to better match them. While the Decoy and Spy did not gain any new powers of attack, they did gain greater mobility and greater powers of detection.

The notation for this game has to include enough information to replay every move but not so much that the players know what each other's pieces are. Game Courier handles this by using a consistent and repeatable random number generator with a fixed seed value. By using a repeatable series of random values, it can replace piece notation with cyphers. To hide that a Pawn has promoted, and to hide what it has promoted to, it notes the Pawn move to the last rank as a move by the type of piece it is promoting to. Since this gets replaced by a cypher, the opponent cannot distinguish this from a move by another piece.

If a human referee takes on the role of a computer program, he cannot be expected to generate the same random sequence each time a player moves. Instead of doing this, he should keep track of the moves with normal notation for his own record keeping and provide players with a list of past moves that do not include any piece identifiers.

Last revised by Fergus Duniho.