The set-up
White's rook stands in front of its pawn on a8, which is the worst square for it. Black's rook on f6 attacks the pawn from the side, so the white rook cannot leave the a-file without losing the pawn.
Black's king belongs on g7 or h7. From there it covers g8 and h8, the squares the white rook would need for a skewer along the seventh rank once the pawn reaches a7. The position is named after Josef Vancura, who worked out this defence in the 1920s.
When the white king comes
White's only winning try is to bring the king to the pawn. Once the king protects the pawn, the rook on a8 is free to move. So the defender checks the king from the side the moment it arrives.
In the starting position the king on b5 already guards a6, and Rf5+ is the only move that draws. If the king walks up to b6 and b7, keep checking along the ranks. If it hides on b8, it blocks its own rook, and your rook returns to f6 to attack the pawn again.
Typical mistakes
Going behind the pawn while it is still on a6 is a common error. With the white king as close as e3, for example, it loses: the king walks over to the pawn and frees its rook. The side attack is what makes the Vancura work.
Letting your king drift away is the other classic error. With the pawn on a7, the black rook behind it and the black king on f7, White wins with Rh8. If Black takes the pawn, Rh7+ skewers the king and the rook.
Remember
- Attack the pawn from the side
- King on g7 or h7
- Check the king when it guards the pawn
- Do not go behind a pawn on a6