The double cannon is the most direct of the two-cannon mating patterns. Two cannons stacked on the same line fire one behind the other, so whatever the opponent does, they cannot answer both.

1. The structure

The key is two cannons on one line, front and back in support:

  • Both cannons sit on the same file or rank, one in front of the other;
  • The front cannon can check directly using an enemy piece as a screen;
  • The rear cannon uses the front cannon as its screen and is ready to fire next.

Because the two threats come from the same direction but at different layers, one move rarely solves both.

2. Conditions for the mate

  1. Both cannons can reach the same line without being intercepted;
  2. A usable screen exists (an enemy piece, or your own front cannon);
  3. The opposing general is on that line, or can be forced onto it;
  4. The defence cannot answer both threats at once (for example by capturing both cannons).

3. The standard sequence

  1. Red puts both cannons on the file where Black's general stands: front cannon close, rear cannon a little further back;
  2. The front cannon checks using Black's advisor (or another piece) as a screen;
  3. If Black takes the front cannon, the rear cannon checks over a screen at once; if Black blocks, the front cannon has another mating idea;
  4. Black's general has nowhere to go — mate.

The core idea: take one cannon and there is still another.

4. How to defend

  • Exchange a cannon: trading one off is the cleanest cure;
  • Move the general: step it off the cannon's line;
  • Break the screen: remove the screening piece so the cannon has no target;
  • Strike first: create threats with chariot or horse before the double cannon is set up, and disrupt Red's rhythm.

5. Why it matters

The double cannon is useful in both middlegame and endgame, and is at its strongest when the opposing advisors and elephants are depleted and the general is forced up. It differs from the Heaven and Earth Cannons: that pattern works the top and bottom lines, while the double cannon works by stacking on one line.

Practice suggestion: set up "two cannons against a lone general" in single-player mode, practise checking with one cannon first, then build the double cannon so that the defence cannot take everything.

Further reading: Heaven and Earth Cannons and The Iron Bolt Mate.