◇ Just read — no move neededThe front cannon is the carriage
重炮 stacks two cannons on one line to the king: the front cannon sits at the palace heart e8, and the rear cannon — arriving on the same file — fires THROUGH the front cannon straight at the king. The soldier on d8 guards the front cannon, so the king cannot take it, and the advisors can neither interpose below (they cannot reach the file) nor eat the front cannon without becoming the new screen themselves.