Sea battle rules

Two players, two grids of a hundred squares, and ten ships each that the other one cannot see. You take turns calling out a square. They tell you whether you hit anything. First to sink the other fleet wins.

That is the whole game, and it has been played on the back page of exercise books for over a century. What follows is the version played here: ten ships that may not touch.

The board

Each player has a grid ten squares by ten. Columns are lettered A to J, rows are numbered 1 to 10, so every square has a name: C4, H9, A1.

You keep two grids in front of you. One holds your own fleet and the shots fired at it. The other starts empty and fills up with what you learn about your opponent's waters.

The fleet

Ten ships, twenty squares in total out of the hundred:

Ship	Length	How many
Battleship	4 squares	1
Cruiser	3 squares	2
Destroyer	2 squares	3
Boat	1 square	4

A fleet laid out by the rules: ten ships, and none of them touches another.

Placing them

A ship lies horizontally or vertically, never diagonally, and never bent around a corner. It must fit entirely on the grid.

The rule that shapes the whole game: ships may not touch each other. Not side by side, and not corner to corner. There has to be at least one empty square between any two ships, in every direction including the diagonals.

Allowed: water all round every ship. Nothing else may go on the dotted squares.

Not allowed: ships side by side, or touching at a corner.

This is not a formality. It is what makes the next two rules possible, and it is why twenty of your hundred squares are taken but far more than twenty are spoken for.

Taking turns

You call a square. Your opponent tells you one of three things:

Miss. Nothing there. Your turn ends.
Hit. You clipped a ship, but it is still afloat.
Sunk, and which ship it was.

Your chart of their waters: a splash for every miss, a red cross for every hit.

A hit earns another shot. You keep firing until you miss, which means a lucky run can take out half a fleet in one turn. It also means the game swings: a player who finds a cruiser on their first shot can be three ships up before the other has fired twice.

You may not fire at the same square twice.

What happens when a ship goes down

When the last square of a ship is hit, it sinks, and every square touching it is marked as a miss — the whole ring around the wreck, corners included.

A cruiser sunk: the wreck in red, and the ring of water round it marked for you, lighter than the misses you fired.

You are not being given a present. Because ships may not touch, those squares were already known to be empty; marking them just saves everyone the trouble of firing into water they had already ruled out. And you cannot fire there afterwards: those squares are spent.

This is why the no-touching rule and the ring are a pair. Take away no-touching and the ring would be a lie — a square next to a wreck could hold another ship.

Winning

Sink all ten enemy ships. The game itself never ends in a stalemate; someone runs out of fleet. At a table with a friend, though, you can call it a draw between you: either player may offer a draw, and the other accepts or declines — firing instead of answering declines it too. One offer per shot.

Playing a friend

Open a table and send your friend the link. You each lay out your fleet; when your friend has placed theirs, they press Ready, and whoever opened the table sees it and presses Start once their own fleet is down. Nothing is fired, and no clock runs, until then.

After a game, Play again sets up the next one at the same table and keeps the score.