How a windmill works
The standard set-up has the enemy king on h8, a bishop or queen aiming at it along the long diagonal, and a rook on g7 blocking that diagonal. When the rook moves along the seventh rank it uncovers check from the bishop, and it can capture something as it goes. The king has to step to g8. The rook then returns to g7 with check, protected by the bishop, and the king has to go back to h8. The cycle repeats.
Each turn of the windmill costs the attacker nothing and wins whatever the rook captures, because the opponent is in check every move and never gets a free move.
What makes it possible
Three conditions matter. The king must have only one square each time. The rook on g7 must be protected, so the king cannot take it. And the opponent must have nothing that can capture the bishop, block the diagonal or take the rook when it returns. A queen or rook on the seventh rank is dangerous for the attacker, because once the rank is cleared it can capture on g7.
The best-known example is Torre against Emanuel Lasker at Moscow 1925, where a rook on the seventh rank collected several pawns and won back the queen.
How to defend
Break the alignment early, before the cycle begins: capture or block the diagonal piece, give the king a second square, or keep a piece that can take on g7. Once the windmill is turning, it is usually too late to do more than choose which material to lose.
Common mistakes
- Allowing a rook to sit on the seventh rank in front of an enemy bishop or queen aimed at your king.
- Rushing the windmill when the opponent has a piece that can capture on g7 once the rank is cleared.
Questions about windmill
What is a windmill in chess?
A series of alternating checks and discovered checks, usually by a rook and bishop, that lets the rook capture piece after piece while the king shuttles between two squares.
Which pieces make a windmill?
Most often a rook with a bishop behind it. A rook with a queen can do the same, and other pairs are possible in rare positions.