X-ray attack in chess: what it is, with 3 examples

What is an x-ray in chess?

An x-ray is a tactic where a long-range piece (a rook, a bishop or a queen) attacks or defends a square through another piece standing in the way. Right now it cannot reach that square. But as soon as the piece in between moves or gets taken, the line opens and the x-ray piece is there.

That is why x-rays are so easy to miss. When you count how many pieces attack a square and how many defend it, you count the ones that see it now. The piece hiding behind another one does not look like it is part of the fight, until it is.

The x-ray is close to two other tactics. In a skewer, a piece attacks a valuable piece, which moves away and leaves the piece behind it to be taken. In a battery, two of your own pieces line up on the same file or diagonal. An x-ray is the case where the piece in the middle belongs to the opponent.

Example 1: the rook that sees through an enemy rook

The black rook on c8 guards the back rank, and it seems to guard d8 too. But look at the white rook on a8: it sits on the same rank, behind the black rook. It is aiming at d8 through the rook on c8.

1.Qd8+! The queen goes to d8, defended by nobody, it seems. 1...Rxd8 is forced, and now the black rook has left c8. The white rook sees all the way to d8: 2.Rxd8 is mate. Black’s king is stuck behind its own pawns, and the rook that was defending the back rank was taken away by the queen sacrifice.

Example 2: the rook that wins a rook through another rook

White has just put the queen on e2 to trade queens. The trade looks safe: after 1...Qxe2, the rook on d2 takes back.

But the black rook on c2 is looking along the second rank, through the white rook on d2, at the e2 square. 1...Qxe2! 2.Rxe2 (the rook leaves d2, and the second rank opens) 2...Rxe2. Black was a pawn down and has won a whole rook.

This is the most common x-ray in real games: a trade that looks equal on paper, because one of the pieces that will take back is hidden behind a piece that is about to move.

Example 3: the bishop behind the bishop

White’s bishop has just come to c5. The rook on b4 looks well defended by it. But behind the white bishop, on the same diagonal, stands the black bishop on e7: it is aiming at b4 through c5.

1...Rxb4! 2.Bxb4 Bxb4. The white bishop took back on b4 and left c5, so the black bishop goes all the way down the diagonal and takes it. Black has won a bishop for nothing.

How to spot x-rays in your own games

1. When you count attackers and defenders on a square, also look along the lines behind each piece. A rook behind a rook, a bishop behind a bishop, a queen behind anything on a file or diagonal.
2. Before a trade, ask who takes back last. The piece that ends the sequence is often one that only appears once the first capture is made.
3. When your opponent’s piece stands between your long-range piece and something valuable, ask what happens if that piece has to move. A check or a capture that forces it away is often the whole combination.
4. Watch your own back rank. Many x-rays end in mate because a rook that defended the last rank is pulled away.

You can train x-rays on puzzles, but the ones that cost you points are the ones in your own games: the trades you misjudged and the back-rank mates you did not see coming. Those keep coming back in the same kind of positions.