Battleship

How to play

Place five ships on your grid, using rotate to turn one upright, or take a random fleet. Then take turns firing at squares in enemy waters. A hit is marked in red and a miss in white, and a ship is sunk when every one of its squares is hit. Sink all five enemy ships before the computer sinks yours. The computer does not fire blindly: once it lands a hit it works out the likely direction and follows the ship along it, so a careless spread of your fleet will be punished.

Tips

• Do not hug the edges. Ships pushed against a wall are found quickly once the hunt starts.
• Avoid touching your own ships together. A single hit then leads straight into the next one.
• Fire in a diagonal lattice rather than sweeping rows. No ship of length two can hide from it.
• After a hit, finish that ship before looking elsewhere. A wounded ship is the cheapest one to sink.
• Track the lengths you have already sunk. Knowing only the five remains changes where it can fit.

How the computer hunts

A naive opponent fires at random and takes far too long to find anything. This one uses the standard two mode approach. In hunt mode it fires on a checkerboard lattice, because no ship is shorter than two squares and a lattice covers every possible position with half the shots. On a hit it switches to target mode, queues the four neighbouring squares, and after a second hit works out the ship's direction and follows the line until the ship sinks. Then it goes back to hunting.

That is roughly how a competent human plays too, which is why the placement advice matters. A fleet that touches or hugs the walls gets found in a chain: one hit leads straight into the next ship.

Placing and shooting

• Spread the fleet. Ships that touch mean one hit exposes two ships.
• Avoid the edges. A ship against a wall has fewer squares of empty water around it to hide in.
• Shoot on a lattice yourself. Every other square, like a checkerboard. No two square ship can hide from it.
• Finish a wounded ship before hunting elsewhere. It is the cheapest ship on the board to sink.
• Track what has sunk. Once the carrier is gone, no five square gap needs checking any more.

Common questions

How many ships are there?

Five, of lengths 5, 4, 3, 3 and 2, for a total of 17 squares.

Does the computer cheat?

No. It hunts on a lattice and follows hits along a line, the same way a careful human plays. It has no knowledge of your placement.

Can ships touch each other?

Yes, the rules allow it, but it is a bad idea: a hit on one leads the hunt directly into the other.