The River-Patrol Cannon

What is the river-patrol cannon?

Red puts both cannons to work in this system, one on the centre file and one on the river bank. It starts with 炮二平五 (C2=5), which brings the first cannon to e2, where it attacks Black's soldier on e6. Both sides then develop, Red with a horse and a chariot and Black with both horses and a chariot. On Red's fourth move, 炮八进二 (C8+2) takes the second cannon straight up from b2 to b4.

The board in this section shades the river, which runs between ranks 4 and 5, and marks the cannon on b4 with a ring. That cannon stands on the last rank before the river, and it is the river-patrol cannon of the system's name. When it arrives, no other piece stands on rank 4, so it can move along the rank to either wing in one move.

The central cannon against the screen horses can turn into several systems, and this is one of them. The ECCO, a code list of xiangqi openings, gives the central cannon with a river-patrol cannon against the screen horses the codes C81 to C86.

The course line, move by move

The board below plays the line that Xiangqi Arena's opening course teaches for the river-patrol cannon. It begins with the system's standard moves, and a computer engine continued it from there. You can step through its first twelve moves, six for each side, with a note on each.

After the cannon reaches b4, Red brings out the second horse from b0 to c2 and then advances the chariot from h0 to h4. From h4 the chariot attacks the cannon on h7 and guards the cannon on b4 along rank 4. Black pushes the soldiers on g6 and c6 one point each, then moves an elephant to e7, where it guards both soldiers.

The course has two drills on the same line, and both go on past the twelve moves shown here. In one you play Red's moves yourself, and in the other you take Black and defend against them.

Black's answers in the archive

The board in this section reaches the river-patrol cannon by another order of moves. Red pushes the soldier on c3 and brings out the second horse before the cannon moves, while the chariot on i0 is still at home, so 炮八进二 (C8+2) comes on Red's fifth move. In the archive, 227 games reached this position, and the arrows show Black's three most common replies, each with its share of those games.

The first two lines below continue with the two most common replies: the horse jump from g7 to h5 and the elephant move from g9 to e7. The third shows the same cannon move in another opening, after Black has answered the central cannon with a central cannon of its own. If your opponents meet the central cannon with the screen horses, start with the first two lines. If they answer with a central cannon, turn to the third.

The five opening principles in this line

Five principles sum up good opening play: bring the chariots out early, do not move one piece again and again, do not grab soldiers, keep both wings in balance, and keep the general safe. Use them as a checklist when you study a line or look back over your own games.

The chariots show the first two. Each side brings one chariot out within its first three moves, Black's to h9 and Red's to h0, while the chariots on a0 and a9 stay in their corners for all twelve moves. Red's chariot is also the only piece that moves twice, and its second move, from h0 to h4, attacks the cannon on h7 and guards the cannon on b4 at once.

The third and fifth principles hold as well. No piece is captured in the twelve moves, and both generals stay on their starting points.

Common mistakes

The first mistake is taking the soldier on e6 with the central cannon. The cannon attacks that soldier throughout the twelve moves, so the capture can look free. But Black's horse on g7 has guarded e6 since Black's first move, and both horses have guarded it since Black's third. A horse takes back, and Red has given a cannon for a soldier.

The second is taking the cannon on h7 with the chariot. Red's chariot attacks that cannon from h0 on Red's third move and from h4 on Red's sixth, but Black's chariot on h9 guards it all along. If Red takes, Black's chariot takes back, and Red has traded its strongest piece for a cannon. In the course line the chariot leaves that cannon alone and keeps attacking it, while from h4 it also guards the cannon on b4.

The third is moving the river-patrol cannon again too soon. From b4 it can slide along the open rank, so it is tempting to keep shifting it toward a target. In the course line Red leaves it there and spends the next two moves on the second horse, from b0 to c2, and on the chariot, from h0 to h4. Moving the cannon again before that horse is out breaks the second principle and leaves Red's left wing behind the right.

How does the system score in the archive?

In the archive's games with the river-patrol cannon, Red won 39%, 36% were drawn and Black won 25%. A game lasted 44 moves on average. For comparison, Red wins 37% of all 29,164 human games in the archive, and 36% end in a draw.

As Red, Li Shaogeng has played the system most often, in 52 games, and Wan Chunlin has the best score, 66.7% over 42 games. As Black, Xu Tianhong has faced it most often, in 28 games.

At the end of this section you can replay one archive game with the system, move by move. When the course line feels familiar, practise it in the two course drills, then try the system as Red in a few games against the computer. It will not win games by itself, but it gives your second cannon a clear place to stand.