How does a cannon work with a soldier as its screen?
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 soldier is one of the most efficient screens a cannon can use, because it is nearly worthless on its own, so the opponent rarely wants to spend a move capturing it, and it is usually already heading toward the enemy position, so it does double duty as an advancing threat and a working screen at the same time.
A common attacking shape
A crossed soldier sitting on a file with a cannon behind it, both aimed at the enemy palace, is a recurring attacking formation. The soldier threatens to step in and cause trouble on its own, while the cannon behind it threatens whatever lies beyond it the moment the soldier advances or is captured and replaced.
Why removing the screen is awkward for the defender
Capturing the soldier screen usually costs the defender a tempo and sometimes opens the very line the cannon wanted opened in the first place. A defender often has to leave the soldier alone and deal with the threat some other way, which is exactly the bind the attacker is looking for.
Related questions
Is a soldier a better screen than a piece of higher value?
Often yes, tactically, simply because losing it costs so little that the opponent has less incentive to remove it.
Can the soldier itself capture using the cannon's threat?
No, the soldier still only ever moves and captures like a soldier; it just happens to be standing where the cannon needs a screen.
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