X-ray attacks: pressure through a piece
The attack that is not an attack yet. Nothing is threatened this move, and everything is threatened the moment the piece in the middle moves.
- 120 positions in the course
- Difficulty 739–2326
- Section: Sharper Tactics
- 5 levels
What an x-ray is
An x-ray is a line attack that passes through a piece to something behind it. Right now the front piece blocks it, so nothing is hanging. But the line exists, and every calculation in the position has to account for what happens when that front piece is captured, moves, or is deflected.
It is used in two ways. Offensively, an x-ray means a capture on the front piece is safe because your own piece behind recaptures -- or that the enemy piece behind is really the target. Defensively, an x-ray is why a piece that appears undefended is not: the defence arrives through another piece.
How to spot it
- Trace every open and half-open line to the end, through pieces, not up to them.
- Look for your rook behind their rook, or your queen behind their bishop. The piece in the middle is the only thing making the position quiet.
- In endgames, check whether your rook x-rays theirs through a pawn. That is where most x-ray defences come from.
- If a capture looks like it loses material, count again with the x-ray included. It very often does not.
Three x-ray positions
Three positions from the 120 in this skill, easiest first. The highlighted squares are the move your opponent has just played. Work it out before you open the answer.
Position 1
White to move. Find the best move.
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24...Rxe2 25.Rxe8+ Rxe8 26.Rxe8#
The line ends in checkmate. The attack works through the piece in the middle, so the moment that piece is captured or forced to move the line behind it decides things.
The position comes from an endgame of a real game, rated 739 for difficulty. The answer reaches checkmate.
Position 2
White to move. Find the best move.
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34...fxe3 35.Qxf8+ Rxf8 36.Rxf8#
The line ends in checkmate. The attack works through the piece in the middle, so the moment that piece is captured or forced to move the line behind it decides things.
The position comes from the middlegame of a real game, rated 1354 for difficulty. The answer reaches checkmate.
Position 3
Black to move. Find the best move.
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31.b3 31...Nd2 32.Rxd2 32...Rxd2
The line comes out 2 pawns ahead. The attack works through the piece in the middle, so the moment that piece is captured or forced to move the line behind it decides things.
The position comes from an endgame of a real game, rated 1871 for difficulty. The answer reaches a clear advantage.
X-ray as a defence
The most valuable use of the pattern is defensive and it is badly under-taught. A rook that appears to be defending nothing is often defending a square through an enemy piece, which means the enemy capture on that square simply loses a piece.
When you are checking whether a piece of yours is safe, count defenders through pieces as well as directly. A great many positions that look lost by one tempo are held by an x-ray nobody counted.
Questions people ask
What is an x-ray attack in chess?
An attack along a rank, file or diagonal that passes through an intervening piece to a target behind it. It does not threaten anything immediately, but it decides what happens the moment the middle piece moves or is captured.
What is the difference between an x-ray and a skewer?
A skewer is an immediate attack -- the front piece is under fire right now and must move. An x-ray is latent: the front piece is not being attacked, and the line only matters once it leaves. Every skewer is a line attack; not every line attack is a skewer.
Can an x-ray be defensive?
Yes, and that is its most useful form. A piece defending a square through an enemy piece is still defending it, which turns apparently winning captures into losing ones.
Nearby patterns
X-Ray sits in Sharper Tactics. The rest of that section:
- Discovered AttacksMove one piece, attack with another
- Double CheckTwo checks at once, king must move
- DeflectionDrag the defender away
- AttractionLure a piece to a bad square
- ClearanceGet out of your own way
Tell it apart from its neighbour
X-Ray is confused with these more often than anything else, and the difference is usually one sentence long.