How to play Fleet Hunt

Fleet Hunt is naval battle by deduction. Two ten-by-ten grids, two hidden fleets, and one shot a turn.

The fleets

Each side has the same five ships, seventeen cells in total on a hundred-cell grid:

The Carrier is five cells, the Battleship four, the Cruiser three, the Submarine three, and the Destroyer two. Ships are placed horizontally or vertically, never diagonally, and never overlapping. You can randomise your own layout as many times as you like before you start.

Firing

Take turns firing one shot at a single cell of the enemy grid. A hit is marked in red, a miss with a splash. When every cell of a ship has been hit it sinks, and you are told which ship it was.

That last detail matters more than it looks. Being told the Cruiser has sunk tells you three cells are accounted for, so any further hits nearby belong to a different ship — and it tells you the Submarine, also three cells, is still out there somewhere.

You win by sinking all five enemy ships before yours go under.

Hunting properly

Random shooting is close to the worst way to play. Two ideas do nearly all the work.

The first is parity. The smallest ship is two cells long, so it must cover one cell of every pair. That means you never need to shoot every square to find something — firing on a checkerboard of every other square is guaranteed to touch every ship on the board, and it halves the number of shots the search takes. Once the two-cell Destroyer has sunk, the smallest remaining ship is three cells, and you can spread your search out to every third square.

The second is target mode. The moment you get a hit, stop searching. Fire at the four cells around the hit until you get a second one, then you know the ship's direction — carry on along that line in both directions until it sinks. Going back to random shooting after a single hit throws away the most valuable information in the game.

Defending

The computer fires back and it uses exactly the ideas above: it sweeps efficiently while hunting, and locks on the moment it lands a hit, working outward and then along the line until the ship is gone.

So how you lay your own fleet matters. Ships flush against each other are dangerous, because a lock-on that finishes one ship immediately finds the next. Edges feel safe and are not especially — but they do cut the number of directions an attacker has to check after a hit, which slightly favours the defender. Spreading the fleet with gaps between ships is the reliable choice.

Track the computer's shots on your own grid as they come in. Once you can see it has switched into target mode on one of your ships, you know which of your ships is about to go, and you know roughly which of your other ships are still safe.