Chess960 tactic on a7 (b7)
c9-13718naming tag (square·N)Opens in the app if installed, otherwise downloads the APK.
The tactical motive
Chess960 twist: use the unusual starting setup of the pieces.
Mate: a forcing sequence that ends the game — the king has no escape.
Mate in 4: a forced checkmate in four moves — every reply is covered.
Difficulty 2350 ShuffleRating — expert level — few solve it at first try.
White to move — find the best continuation
How to recognize this tactic
In Chess960 the pieces start on unfamiliar squares, so tactics appear earlier and from unusual angles. Do not trust classical patterns — read the actual lines of the bishops, the rooks and the queen from where they really stand in this position.
This is a forced mating attack. Start from the enemy king: which of its squares are already covered, and which move takes away the rest while keeping the king in check? Forcing moves — checks and captures — are what turn an attack into mate.
A mate in four is a longer forced net: each of your moves is a check or an irresistible threat, and the king is driven step by step to a square where it is finally trapped. Verify that the defender has exactly one reply at every branch.
General method: before you move, list the forcing candidates — every check, every capture, every direct threat — and calculate those first. The solution to a tactic is almost always among them.
Position on the board
White: king b1, rook b7 c7, knight f5, pawn a3 g3 d4 e4 a5.
Black: king a8, rook g5 e8, knight f2, pawn b5 f6 e7 h7.
9 white and 8 black pieces are on the board; the puzzle position arises after move 36.
The position in numbers
White are ahead by 1 points of material (18 against 17; pawn = 1, knight and bishop = 3, rook = 5, queen = 9) — the tactic has to convert or outweigh that.
The white king stands on b1, the black king on a8.
It is White to move on move 36, with 29 legal replies to weigh — only the line that keeps the advantage solves the puzzle.
White keeps 5 pawns, Black 4. Files fully open (no pawns of either colour): c — natural highways for the rooks and queen. Half-open for White: b, f, h.
The White king has 5 empty squares to step to right now — the fewer they are, the closer a mating net.
Solution & explanation
Main line
36. Ra7+ Kb8 37. Rcb7+ Kc8 38. a6 Nxe4 39. Ra8#
Why it works
- Best move. rook to a7 is exactly what the engine plays (#3).
- Spot on — rook to b7 (#2).
- A natural move: pawn to a6.
- Best move. rook to a8 is exactly what the engine plays (#).
- The line ends in a forced mate in 4.
- If instead Kb8, then Rcb7+ and you stay on top.
Move by move
- 36. Ra7+ — rook to a7 with check
- Kb8 — king to b8
- 37. Rcb7+ — rook to b7 with check
- Kc8 — king to c8
- 38. a6 — pawn to a6
- Nxe4 — knight to e4 (capture)
- 39. Ra8# — rook to a8 and it is checkmate
Types in this puzzle
Ladder mate
Two heavy pieces climb line by line, cutting off every retreat.
The ladder mate uses two heavy pieces climbing rung by rung: one cuts the king off along a line, the other checks on the next line, driving him toward the edge. It is the classic two-rook technique — check, the king retreats one rank, the other rook checks, until mate on the last rank. The only danger is the king creeping close enough to attack one of your rooks. If it does, simply slide that rook to the far side of the same line.
Mate in 4+
A long forced mating combination.
Mate in four or longer is a marathon of forcing moves where the grip must never loosen. The tools are the same: checks, double threats and sacrifices that deny the opponent a single free tempo. Do not juggle the whole tree at once — walk the main line all the way to mate first, then verify the side branches. If somewhere the defender finds one quiet move that holds, your very first move was wrong.
Passed pawn
Nothing can stop the passer — escort it to the last rank.
A passed pawn has no enemy pawns in front of it or on the neighboring files: only pieces can stop it. Check who can blockade the pawn or catch it with the king — if nobody can, the pawn is worth a whole piece. Push the passer with your pieces supporting it, and put your rook behind it. The beginner's mistake is shoving the pawn forward unprotected, straight into a capture.
About this position
These pieces come from starting position #754.
SP-754 · BastionGuard — Both knights begin inside the board while the king stands on c or f; a position and its mirror twin share this family.
The king starts on c1, the rooks on b1 and g1, the queen on h1.
The king already stands on c1, so castling long moves only the rook, from b1 to d1.
A bishop starts in the corner on a1: it has a single diagonal, which the b-pawn unlocks, running out to h8.
One second-rank pawn starts with no defender at all: a2.
The setup belongs to the BastionGuard family; read right to left it becomes position 391.
The engine's main line opens with b3.
Morozov Balance Index: 78 of 100 — class A — most balanced. Engine evaluation of the starting position: +18 centipawns for White (depth 42, 400 000 000 nodes).
Explore position #754Provenance
Mined from the project's engine self-play games.
Pack 015 · SP-754
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