The Cannon is as mobile as the Chariot. However, its gun power will be lost without another piece to serve as the ‘carriage’. In essential checkmates involving a Chariot and a Cannon, the Cannon is making use of enemy defenders, i.e. an Elephants or an Adviser, as its ‘carriage’.
(1) The Iron Bolt
In fig. 1, the Red Cannon immobilizes two Black defenders in the central file. This is a fatal pin; any move with the pinned pieces becomes illegal as it will put the Black King in check. Black’s empty baseline on his left wing is vulnerable to attack by an enemy Chariot. It is a checkmate when Red plays R1+7 in this instance. Likewise, a Red Chariot along the 2nd or 3rd file will deliver a similar checkmate.
What if the Red Chariot is on the 4th file? Invading the B60 spot alone is now suicidal, as the opponent King could simply capture it. Here the Chariot check must be supported. In practice, it is often the King who gives the support, as in fig. 2.
Most Chinese xiangqi books assign the name“铁门栓”(Iron Bolt) only to the scenario in fig. 2. I see no reason why the other three positions mentioned in fig. 1 should not be included.
fig. 1
fig. 2
fig. 3
The Pawn could work from B70, and the Horse from B81.
fig. 4
Although the Cannon at the baseline has a similar pinning effect, R6=5 gives no checkmate.
When the check is made at B40 or B60, the assassin has to be supported by a comrade. In Chinese xiangqi books, the checkmate pattern in fig. 4 is also named ‘Heaven and Earth Cannons’. In essence, however, it is the Iron Bolt. The term is used loosely in various checkmating combinations where the offensive side has one Cannon posted along the centre file, and the other at the opponent’s baseline.
The Iron Bolt is a deadly weapon because of the Cannon pin in the central file. Please go to the next page to see examples of checkmating combinations employing the Iron Bolt.