Three-dimensional chess
Three-dimensional chess was a variant of the ancient Earth board game chess. 

It was an accustomed pastime of Kirk and Spock aboard the  in the 23rd century and its popularity extended into the 24th century.

Play 
Three-dimensional chess incorporated traditional chess pieces on a chess board of varying designs, for example three levels with the secondary and tertiary levels each having two smaller platforms located between that level and the level above, known as a "half-level". Movement of pieces was similar to that of traditional chess, with the main difference being that in the course of a move, pieces were moved up or down any number of levels. 

According to Spock, "the principles of three-dimensional chess are basically mathematic." The game's set up included the placement of the majority of the black pieces on the secondary level and the majority of the white pieces on the tertiary level. () 

Example moves in the game play included: 

 "Rook to king's pawn four."
 "Bishop, half level right."
– Spock versus the computer ()

 "Pawn to queen four, king's level."
 "Pawn to king's bishop three, queen's level." 
– Nibor versus Riker ()

In 2268, Kirk used a chess problem as a security measure while visiting Elba II to hamper any unauthorized transports to the Enterprise. His chess problem sought the response to the move "queen to queen's level three". When pressed for the answer by Garth, Kirk coyly responded that "I'm sure you're aware that there are an infinite number of countermoves." The move Kirk ultimately chose for his countersign and response to the move was "Queen to king's level one." ()

Strategy 
While often perceived as a game of logic, Spock found that Kirk's "illogical approach to chess does have its advantages on occasion." Kirk said that he'd "prefer to call it inspired." ()

According to Deanna Troi, this form of "chess isn't just a game of ploys and gambits. It's a game of intuition. ()

The  could be coupled with the Aldabren Exchange to lead to an effective defeat of a rival. () 

In pitting one maneuver against another, the Kriskov Gambit was often the response used to counter an el-Mitra Exchange. ()

 History 
Captain Philippa Georgiou kept a three-dimensional chess board in her ready room on the . ()

At least as early as 2257, Spock kept a three-dimensional chess board in his quarters on the . ()

That year, his foster sister, Michael Burnham, brought a three-dimensional chess set out of storage in her quarters while Spock was visiting her there. Although he was initially somewhat puzzled by the gesture because he didn't know how it could aid him in attempting to contemplate the Red Angel, Burnham suggested that the game might help Spock consider the Red Angel logically, since the game itself represented logic. Accusing Spock of being frightened of losing, Burnham challenged him to a game, which he then accepted. However, Spock proceeded to play a series of moves that Burnham was baffled by and considered illogical, though he executed them in an effort to defy her expectations. When their conflict verbally and emotionally escalated, Spock struck the chess board with his right hand, causing it and the pieces still on the board to fall to the floor in disarray. () The pieces and board were later sorted back into place and Spock subsequently invited Burnham to make the first move of a new game between them, which she proceeded to act on. ()

In general, Spock was an exceptional chess player, and his game was consistently logical. However, he often had a difficult time predicting or effectively responding to unexpected moves made by Captain Kirk, whom he was often beaten by. () When it seemed that Kirk was going to be court martialed in 2267, he spoke of the circumstances, telling him, "It's not all bad, Mister Spock. Who knows. You may be able to beat your next captain at chess." ()

Charles Evans watched the crew of the Antares play three-dimensional chess while he was transported aboard that ship. Following his arrival aboard the Enterprise, he asked for a chance to play, and was matched against the "chess master" Spock. After losing in three moves, he destroyed all of the white chess pieces. ()

Spock also enjoyed playing chess against a rival logical mind, that of the Enterprise computer, which he programmed himself. In 2266, he detected programming errors in the computer's databanks because of faulty chess moves made by the computer, causing him to defeat the computer four times – a feat, according to Dr. McCoy, that was "impossible", as Spock proceeded to demonstrate his fifth win. He later introduced the tampering and unreliability of the computer's records as defense evidence in the court martial of Captain Kirk. At the court martial, he attested that "I personally programmed the computer for chess months ago. I gave the machine an understanding of the game equal to my own. The computer cannot make an error and assuming that I do not either, the best that could normally be hoped for would be stalemate after stalemate, and yet I beat the machine five times. Someone, either accidentally or deliberately, adjusted the programming and therefore the memory banks of that computer." ()

In 2268, Spock played a game of chess against Kelvan expedition leader Rojan. He observed, during their match, that Rojan's game was "off." ()

A problem based on a type of three-dimensional chess on a spherical board was part of a memory test Spock took in 2286. ()

A group of genetically enhanced children at the Darwin Genetic Research Station played three-dimensional chess by using telekinetic abilities they had been given. ()

In 2366, Commander William T. Riker defeated both Ferengi Doctor Farek and Nibor at a presumably alien variant of 3D chess. The former defeat was in Ten Forward was in thirty moves, and the latter took place while Riker was a captive of the Ferengi, along with both Counselor Deanna Troi and her mother, Lwaxana Troi. ()

Reginald Barclay analyzed a chess game after being altered by the Cytherians. He made a move that would force checkmate within nine moves, despite not having previously been a player of the game. ()

Two years later, Counselor Troi managed to beat Lieutenant Commander Data at a game of 3D chess in Ten Forward, prompting Data to honor a bet they had agreed upon, whereby Data was to make Troi a Samarian sunset in the "traditional style." ()

Commander Benjamin Sisko, also a fan of the game, kept a three-dimensional chess set in his quarters aboard Deep Space 9. ()

A three-dimensional chess board was among the various items Ensign Brad Boimler's friends stashed on his former bunk after he transferred to the  in 2380. ()

In 2399, residents of Coppelius Station played three-dimensional chess. Also, a single board and pieces were seen on a tabletop in Jean-Luc Picard's quarters at the station. ()

Appendices
Appearances

 See also 
 Space Checkers (aka three-dimensional checkers)

 Background information 
This game was first identified as "three-dimensional chess" in "Charlie X". In most all other instances, it was referred to simply as "chess".

A call sheet from the episode , dated , listed three-dimensional chess as one of the required items from the art department in the special instructions section. Here, it was referred to as "Okuda chess set".

Collectibles company Franklin Mint produced two different tridimensional chess sets; one based on the TOS four "attack board" version, and a second based on the TNG six-boarded version.

The Noble Collection later released a larger sized TOS tridimensional chess set.

According to the Star Fleet Technical Manual, the starting positions of king and queen pieces are on their own respective attack boards with their own set of rooks and pawns. Knights, bishops, and the remaining pawns occupy the first two ranks of each color's fixed boards.

 Apocrypha 
The Pocket Books  "The Klingon Gambit" additionally made several references to three-dimensional chess.

The novel Tunnel Through the Stars describes a famous 3D chess player named Durania, for whom the classic Duranian Defense is named. He once played a famous game in which his opponent mistook his retreat (the Duranian Defense) for an attack, and broke off their relentless offensive in order to castle with the rook. This moment of hesitation allowed the opponent to get the momentum. The game went on for another four days, but Durania's opponent eventually lost.

The novelization of  makes a quick – and foreshadowing – reference; as the two fight their way through the Narada (largely a fistfight rather than the gun battle seen in the film), , marveling at 's highly effective use of Suus Mahna (thinking to himself, "he even fights logically"), concluded, correctly, that the Vulcan must play a "mean game" of 3-D chess.

A game of three-dimensional chess figures in the first appearance of Kirk and Spock in the  video game , when their game play is interrupted by a distress call coming from the Helios station, just after the captain's tactical error is exploited by the Vulcan. After Spock leaves his quarters, Kirk sneaks back into the room and moves the Vulcan's piece surreptitiously. This version is somewhat different in that the attack board may be suspended below the main board.

At the end of the the Star Trek: Ongoing story arc The Q Gambit'', Kirk and Spock discuss whether or not the future that Q showed them will come to pass and whether or not they will see the omnipotent being again before deciding to play a round of three-dimensional chess.

External links 
 
 
 
 
 
 
 
 , the free Three Dimensional Chess software

cs:Trojrozměrné šachy
de:Dreidimensionales Schach
fr:Echecs 3D
Recreation