The Iron Bolt is one of the cleanest chariot-and-cannon mates. The name is apt: the cannon bolts the general's gate shut, and the chariot delivers the blow on the rib file.

1. The structure

Two parts:

  • cannon on the centre file — facing the general, closing its route up and into the middle;
  • chariot on the rib file — advancing on the general's side of the palace to check directly.

Because the centre escape is sealed by the cannon and the advisors usually cannot reinforce in time, the chariot's check is often immediately decisive.

2. Conditions

  1. The cannon can hold the centre file, without being driven off or traded;
  2. The chariot can reach the rib file to create a threat along the line;
  3. The defender's advisors and elephants are incomplete, so there are no extra answers;
  4. The general's position is fixed, with no other way out of the threat.

3. A typical sequence

With a red chariot and cannon:

  1. The red cannon slides to the centre file facing the black general, which can no longer move up or into the middle;
  2. The red chariot swings to the rib file on the general's side;
  3. The chariot checks down the rib file; the general has nowhere to go and there is nothing to interpose or capture with — mate.

The order matters: seal the gate first, then check. Reverse it and the defender usually escapes.

4. How to defend

  • Drive the centre cannon away or trade it off early, breaking the precondition;
  • Keep the advisors intact so the general keeps an extra square;
  • Watch the rib file and do not let their chariot reach a checking square easily;
  • Block the centre file if necessary to give the general room.

5. Why it matters

The Iron Bolt appears in both endgames and middlegames, and is especially common once the general has been pushed to one side. The lesson: control of the centre file is often worth more than an extra soldier.

How to practise: set up chariot and cannon against a lone general and mate in the fewest moves. Then add advisors for the defender and work out how to remove them first.

Read next: the cannon-behind-horse and cannon-high-soldier guides.