Double Cannon Checkmate in Xiangqi: How 重炮 Works

What 重炮 means

Here 重 is read chóng, meaning layered or repeated, the same character used for stacking one thing on top of another. So 重炮 is literally "layered cannons". You will also see the names 叠炮 (dié pào, piled cannons) and plain 双炮, double cannon.

The term is used in two ways. Some glossaries give 重炮 to the formation itself, two Cannons lined up front and back on the central file. Lists of basic mates use it for the finishing pattern on any line, and English teaching material commonly shows it on the central file, on a rib file and along the back rank. The picture is the same either way: two barrels, one behind the other.

Why blocking does not work

A Cannon moves like a Chariot, but it can only capture, and therefore only give check, by jumping exactly one piece. Normally that rule helps the defender. Against a single Cannon, sliding any piece onto the line creates a second screen and the check disappears.

With two Cannons the arithmetic changes. Say the rear Cannon is checking through the front one. If the defender puts a piece between the front Cannon and the General, the rear Cannon now has two pieces in its way and falls silent. The front Cannon, however, has exactly one, the new blocker, and it gives check instead. The block has only swapped which Cannon is doing the work.

That leaves four ways out, and it pays to learn them as a list, because the attacker must rule out every one. The defender can capture the rear Cannon, capture the front Cannon, step the General off the line, or put a piece into the gap between the two Cannons. That last option is the one players forget. A piece between the Cannons gives the rear one two screens and leaves the front one with none, so neither of them checks.

A worked example from the hollow cannon

Set this up with Red at the bottom of the board, and read left and right from Red's side. Black has its General on its home point in the middle of the back rank, both Advisors on the two back corners of the palace beside it, and both Elephants on their starting points. Red has one Cannon on the central file at Black's river bank, with nothing at all between it and the General, a second Cannon still on its starting point on Red's left, and its General on its home point.

The front Cannon is what players call a hollow cannon (空头炮, kōng tóu pào): it points straight at the General with no screen, so it gives no check. It is still doing a job. Neither Advisor may step up to the palace centre, because that Advisor would become the Cannon's screen and leave its own General in check. Black's palace is frozen in its starting shape.

Now Red slides the second Cannon along its rank onto the central file, behind the first. The rear Cannon checks through the front one. Go through Black's options. The General cannot step sideways, because its own Advisors stand there. Stepping forward to the palace centre keeps it on the central file, still in check. An Advisor or Elephant that moves onto the file in front of the General becomes a screen for the front Cannon. Nothing Black owns can reach the empty points between the two Cannons, and neither Cannon can be captured. It is checkmate, and we confirmed it with the same rules engine that runs games on XiangqiPlay.

The same idea on other lines

Nothing about the pattern needs the central file. On a rib file, one of the palace's two side files, the Cannons need help with the centre, and your own General can supply it.

Put Black's General on the back corner of its palace on Red's left, with an Advisor on the opposite back corner and an Elephant on its starting point next to that. Stack Red's Cannons on the General's file, one on Black's river bank and one on Red's soldier rank, and keep Red's General on its home point with the central file completely empty. The rear Cannon checks through the front one. Stepping forward keeps Black's General on the file. Stepping sideways onto the central file would leave the two Generals facing each other, which is illegal. The Advisor cannot reach the checking line, so this is mate as well. Red's General quietly covers the one escape point the Cannons cannot.

Along the back rank the geometry is identical, just turned on its side. The Cannons line up along the General's rank from the edge of the board, and something else, often a Soldier, a Horse or one of the defender's own pieces, has to take care of the point in front of the General.

Lining them up in a real game

In practice the pattern usually starts from a Central Cannon. Once the defender's central Soldier has gone, a Cannon with a clear view of the General is a standing threat even without giving check, and the second Cannon needs only one move to join it.

Clear your own pieces first. A central Soldier or a Horse parked on the file counts as a screen too, and three pieces on the line means no check.

Look at the General's side points before anything else. The double cannon only mates when those points are blocked or covered, whether by the defender's own Advisors, by your General down an open file, or by a Horse or Soldier.

Keep the rear Cannon out of reach, often far back on your own side of the river, because a defender who can capture it ends the attack on the spot. And watch the gap: if a defending Chariot, Horse or Cannon can land between your two Cannons, the mate is gone. Cannons standing directly next to each other leave no gap to land in.

How the defender fights back

Most of the defence happens before the Cannons line up. Keep the central file blocked by at least one of your own pieces while the danger lasts; a lone Cannon looking at your General down an open file is the warning sign.

When the check has already arrived, run the four questions. Can you capture the rear Cannon? Can your General take the front Cannon? That works when it stands right next to the General with nothing guarding it, because after the capture the rear Cannon has no screen left. Can the General step off the line? Can anything reach the gap?

The gap is often the saving resource. Take the finished mate from the worked example and give Black one extra piece, a Chariot standing on the left edge of Red's soldier rank. The check is still there, but the Chariot slides across into the space between the two Cannons, and the engine shows that as Black's only legal move. One reply is enough.

Where attackers go wrong

The most common failure is a third piece on the line, whether your own Soldier between the Cannons or a defender's piece you overlooked. Two screens where you expected one means no check.

Next comes ignoring the side points. The check is easy to give; the mate is not, and a General with one free step walks out. Playing the second Cannon too early is the other classic, while the defender can still put an Advisor on the palace centre or trade one Cannon off. Before you commit, count Black's legal replies to your check. If the number is not zero, you have found a check, not a mate.

Practise until you see it

You want to recognise two Cannons on one line at a glance, from either side of the board. XiangqiPlay's free puzzle library holds 5,000 engine-proven mate puzzles to train that eye, and with a free account you can try the pattern against the computer at any of its eight levels, from Easy to God.