What is a cannon on the bottom rank called, and is it strong?
These answers restate the rules implemented by our open-source engine, which follows the WXF laws and is regression-tested against the official 110-diagram repetition casebook. Where an answer refers to a specific position, that position lives on the linked reference page, where the build verifies it against the engine before publishing.
Direct answer
A cannon that drops to the opponent's back rank is called 沉底炮, the sunken-bottom cannon. From there it fires along the rank behind the palace, where the defender's advisors and elephants are, and those pieces make excellent screens — which is exactly the point.
Why it works
The defender's own structure supplies the screen. An advisor or elephant sitting on the back rank is precisely what the cannon needs to fire across, so the more solidly a defender has "protected" the general, the more targets the bottom-rank cannon has.
It pairs naturally with a chariot on the same rank or a second cannon.
Its weakness
It is far from the rest of your army and can be hard to bring back — a cannon cannot go around obstructions. Committing one to the back rank without a follow-up piece is a common way to end up attacking with one piece, which achieves nothing.
Related questions
How do you defend against it?
Move the screens it is using, or block the rank at a point where the count becomes two. Trading it off is often simplest.
Is it worth a soldier to get there?
Frequently, if a second attacker can follow. Not if it arrives alone.
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