The Stonewall Attack is a chess opening; more specifically it is a variation of the Queen's Pawn Game. It is characterized by White playing 1.d4, 2.e3, 3.f4 and 4.c3, usually playing 5.Bd3 as well, even though the moves are not always played in that order (see transposition). The Stonewall is a system White sets up, rather than a specific variation. If White puts up the Stonewall formation it is called a Stonewall regardless of how Black chooses to defend against it. When Black sets up a Stonewall formation, with pawns on c6, d5, e6 and f5, it is a variation of the Dutch Defense.
|This article uses algebraic notation to describe chess moves.|
As the name implies, the Stonewall setup is a solid formation which is hard to overrun by force. If Black fails to react energetically to the Stonewall setup, White may launch a lethal attack on the black king, typically by playing the knight from f3 to e5, advancing the g-pawn to drive away the defending black knight, and making a well-timed bishop sacrifice at h7 (see Greek gift sacrifice) when White can bring one of the major pieces (queen and/or rook) to the h-file. Often this attack is so powerful that White does not need to develop the knight on b1 and bishop on c1. Traditionally, chess computers have been vulnerable to the Stonewall because the positions are usually without clear tactical lines. White simply prepares for an assault by bringing pieces to aggressive posts, without making immediate tactical threats. By the time the computer realizes that its king is under attack, it is often too late. This, however, is not the case with newer chess computers.
The downsides to the Stonewall are the hole on e4, and the fact that the dark-squared bishop on c1 is completely blocked by its own pawns. If Black defends correctly against White's attack, these strategic deficiencies can become quite serious. Because of this, the Stonewall Attack is almost never seen in master-level chess any more, although it is seen occasionally among club players. However, Black playing the Stonewall variation of the Dutch Defense is seen occasionally at master level.
Black has several ways to meet the Stonewall. One choice which must be made is whether to fianchetto one or both bishops; Black can meet the Stonewall with a ...b6 and ...Ba6 aiming to trade off the dangerous white bishop on d3, and a kingside fianchetto with ...g7-g6 takes away White's idea of attacking h7. An early development of Black's light-squared bishop to f5 also cuts across White's plans.
Encyclopedia of Chess Openings
Since the Stonewall system is used against a variety of Black defenses, the Encyclopaedia of Chess Openings has trouble classifying it. Among the codes used are D00 (when Black has played ...d5), A45, and A03, the code for Bird's Opening.
This sample game  illustrates what can happen if Black defends poorly.
1. d4 d5 2. f4 Nf6 3. e3 e6 4. Nf3 c5 5. c3 Nc6 6. Bd3 Bd6 7. O-O O-O 8. Nbd2 b6 9. Ne5 Bb7 10. g4 Qc7 11. g5 Nd7 12. Bxh7+ Kxh7 13. Qh5+ Kg8 14. Rf3 f6 15. Rh3 fxe5 16. g6 1-0
- Brace, Edward (1977). "Stonewall Formation". An Illustrated Dictionary of Chess. Craftwell. ISBN 1-55521-394-4