Iron Echo — Counter-Battery Grid Puzzle

What is Iron Echo — Counter-Battery Grid Puzzle

Iron Echo hides four enemy guns on an eight-by-eight grid and gives you two tools. A scan costs no ammunition and returns one number: the distance, counted in horizontal and vertical steps, from the cell you probed to the nearest gun still firing. A shot spends one of your eight shells and either destroys a gun or leaves a crater. Each reading is drawn as a diamond, because the cells at an equal step-distance from a probe form a diamond rather than a circle. Columns run A to H and rows 1 to 8, so every reading has an address. Where two diamonds cross a gun may sit; where three cross, one usually does.

The difficulty is that the reading is a minimum, not an address. Four guns answer at once and only the closest is reported, so a small number near the middle tells you little, while a large one is a gift: an answer of five proves that every cell within four steps is empty, clearing twenty-five squares in a single action. The enemy is listening too. Every scan and every shot advances an alert meter, and each time it fills, counter-battery fire takes one of your three HQ points. Roughly twenty actions is all your position will bear, and only eight of them can ever be shells.

How to play

1. Press Daily Operation or Skirmish to deploy, then choose Scan or Fire in the command panel; your click on the grid does whatever the selected action says.
2. A scan writes a number into the cell and draws its diamond: the step-distance to the nearest living gun, coloured red when near and blue when far.
3. Switch to Fire and click a cell you trust, spending one of eight shells; a direct hit destroys the gun for two hundred points, a miss leaves only a crater.
4. Each action fills the alert meter, and every time it reaches seven the enemy takes one of your three HQ points. Silence all four guns before the position gives way.

Strategies that work

• Open from a corner. A scan at A1 returns the row plus the column of the nearest gun, so its diamond collapses onto one anti-diagonal of at most eight cells. Two opposite corners, A1 and H8, usually reduce the board to a narrow band for two of your first seven actions.
• Read a large number as a clearance. An answer of four proves that no gun stands within three steps, erasing twenty-five cells at once, while an answer of one says almost nothing about the other three guns. When a probe comes back blue, place the next one on the far side.
• Never fire on a one-in-four guess. A miss costs ninety bonus points plus the shell; a scan costs thirty-five and never runs out. When a reading of one leaves four candidates around it, probe one of them: a zero confirms the gun, and any other answer strikes that neighbour off.
• Guns are never adjacent, diagonals included, so the eight cells touching a gun you have just destroyed are certainly empty. Spend neither scan nor shell on them. It also means a confirmed gun never conceals a second one behind it, which makes your first kill the safest ground on the board.
• Distrust old numbers late on. The figure in a scanned cell is the distance to the nearest gun alive when you probed it, and it is never recalculated; destroy that gun and the number is stale, the real distance larger. A cell cannot be scanned twice, so probe fresh ground instead.

A little history

Iron Echo was written for puzzle-me.com. It belongs to the family of probe-and-deduce grid games that Battleship made familiar, but replaces the hit-or-miss answer with a measured one, turning the board into an exercise in taxicab geometry. Distance is counted in steps rather than in a straight line, the metric credited to Hermann Minkowski and called the Manhattan distance, and under it the points equidistant from a centre form a diamond, not a circle. The framing comes from artillery, where a gun betrays itself the moment it fires: information is never free.

Frequently asked questions