Cannon tactics
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Direct answer
Cannon tactics all follow from one rule: the cannon captures by jumping exactly one piece. That makes the screen the tactical object — move it and the cannon fires, add one and the attack dies. Discovered attacks, batteries down the central file and the classic mates against a stripped palace all come from this.
The discovered attack
Xiangqi's discovered attack works backwards from the chess version. In chess you move a piece out of a line to reveal an attack. Here the screen is what makes the cannon dangerous, so the tactic is about which piece is doing the screening and what happens when it moves — the screen departs, does damage of its own, and the cannon's line changes at the same time.
Red to play below: the chariot on e1 can win a piece by moving along the file.
Red to play and win a piece with the chariot.
Xiangqi position. Red: chariot e1, general e0. Black: general e9, horse b5, cannon h5. Red to move.
Batteries and the central file
Two cannons stacked on the same file, or a cannon behind a chariot, form a battery — and in xiangqi the battery is more dangerous than in chess, because the enemy's own pieces are the ammunition. A cannon aimed at a general through two advisors is not attacking anything yet; remove one advisor and it is mate.
This is why stripping the advisors (破士) is such a standard plan, and why two apparently trivial pieces decide so many games.
Defending against cannons
- Trade pieces. Every exchange removes potential screens. A cannon in a bare position may be unable to capture anything at all.
- Do not supply the screen. Moving one of your own pieces into the line between an enemy cannon and your general is how most cannon accidents happen.
- Add a second piece to the line. Two pieces between cannon and target means no capture — one more piece is a complete defence.
- Keep your advisors and elephants. They are the specific antidote to a central-file cannon.
Related questions
How does a cannon checkmate in xiangqi?
Typically by firing down the central file at a general whose advisors have been removed or forced aside, using a remaining piece as the screen. Cannon-and-horse and cannon-and-chariot mating patterns against a stripped palace are worth learning by heart.
What is a cannon battery?
Two cannons on the same file, or a cannon behind a chariot, so that removing or moving the front piece creates an immediate threat. Batteries aimed at the palace are the backbone of most xiangqi attacks.
How do you defend against a central cannon attack?
Keep both advisors, avoid moving your own pieces into the cannon's line, add a second piece to that line where you can, and trade pieces off — a cannon loses power as the board empties.