Adjutant Chess follows the rules of orthodox chess, with the exception of the extended castling rule. The curious but useful board was invented by king Gustav III of Sweden (see Gustav III's Chess). The extra corner squares (citadels) are also known from medieval big board variants, such as Citadel Chess (14th century?). The board sizes were either 10x10 or 12x12 and had four extra protruding squares that served as sanctuaries for the king. (cf. Pritchard: The Classified Encyclopedia of Chess Variants, p.244)
Extended castle: when castling the king may jump three squares, but it can also jump two as usual. The rook ends up on its usual square. The extended castling rule makes play on the wings easier to achieve. The king can rapidly take control over the kingside or queenside corner square.
Disregarding the situation on the rest of the board, this illustrates how convenient the extra corner square is when launching an attack on the wing. When the king gets out of harm's way, this also makes it easier for the pieces to maneuver.
In an alternative variant, Adjutants are placed on the extra corner squares. The Adjutant slides in any direction, but on the orthogonals it slides only on one colour. The opposite colour squares are simply ignored. The Adjutant's value is 6, that is, the same as rook + pawn, or two light pieces. The Adjutant is really an enhanced bishop that can also move orthogonally. Its main weakness is that it cannot give mate together with the king.
The Adjutant also slides on the orthogonals by ignoring the opposite colour squares. Note that it cannot leap over occupied squares of its own colour.
Yet another variant features the Orthobishop, which slides orthogonally, but on the same square only. It's like an Adjutant without the diagonal movement.
In other variants Kwaggas or Crab pawns are used (see downloadable zip-file).
• You can download my free Adjutant Chess program here (updated 2009-10-16), but you must own the software Zillions of Games to be able to run it (I recommend the download version).
• You can play Adjutant Chess (with empty corner squares) online and by e-mail here.
• You can play Adjutant Chess (with Adjutants) online and by e-mail here.
• Don't miss my other chess variants.
© M. Winther 2008 November