The objective is checkmate and pieces move as in orthodox chess.

Extended castle rule: 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 castle rule makes play on the wings easier to achieve. The king can rapidly take control over the kingside or queenside corner square. This curious but useful board was invented by king Gustav III of Sweden (see Gustav III's Chess).

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 5, that is, the same as a rook. 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.

You can play Adjutant Chess (with Adjutants) online and by e-mail here.

You can play Adjutant Chess (with empty corner squares) online and by e-mail here.