Sea Battle — hunt a hidden fleet free in your browser

Sea Battle is the solo half of the old pencil-and-paper naval game: there is no opponent taking turns against you, just a 10×10 sea with five ships hidden in it — one of 5 cells, one of 4, two of 3 and one of 2 — placed at random, always straight along a row or a column, and never touching each other, not even at a corner. Fire one square at a time. A miss marks the water, a hit marks the ship, and the moment you take a ship's last cell it is announced sunk and struck off the roster.

Your score is simply the number of shots it took to sink all five, so lower is better. The fleet is 17 cells, which makes 17 the theoretical perfect game. Firing blind takes about 95 shots; searching well brings a run to around 50, and anything under 45 is a genuinely good sea. It runs free in any browser with no download, plays one-handed on a phone, and keeps your best hunts on your own device.

How to play

• Tap or click a square to fire at it. Every shot counts, including the ones that hit water.
• A dot means water, a red square means a hit, and a darker red block marks a ship that has gone down.
• When a ship's last cell is hit it is announced as sunk and struck through in the fleet roster under the grid — knowing which lengths are still afloat is half the game.
• The row letters A–J and column numbers 1–10 are there so you can talk about squares (and follow the strategy below) — E5 is row E, column 5.
• On desktop the arrow keys move a highlighted square and Space or Enter fires at it. Between runs, Space or Enter starts a new sea.
• There is no timer and no lives. The only pressure is your shot count, so think before you fire.

Search strategy: how to halve your shot count

Firing at random squares takes about 95 shots to finish the fleet — you end up shooting nearly the whole sea. Three ideas cut that to roughly 50.

Shoot the checkerboard, not the whole sea. The shortest ship is two cells long, and any two cells side by side — across or down — are one dark and one light square on a checkerboard. So a ship cannot fit entirely inside one colour: shooting only the dark squares still cannot miss anything. That halves the 100 squares you would otherwise have to try, from 100 down to 50, without giving up a single ship.

Once you hit, hunt along the axis — not around the cell. A hit is one cell of a straight ship, so the rest of it lies north, south, east or west; never diagonally. Fire the four orthogonal neighbours until a second hit lands, and the moment two hits line up the orientation is settled — a vertical pair can only be part of a vertical ship. From then on only the two ends of that line can extend it, which is two candidate squares instead of eight. And because ships never touch, every square around a ship you have just sunk is water: don't spend shots there.

Widen the stride as the small ships die. The checkerboard is only the right pattern while a 2-cell ship is still out there. Sink it and the shortest ship afloat is 3 cells, and any three in a line covers three consecutive diagonals — so firing only where (row + column) divided by 3 leaves the same remainder still cannot miss, and that is a third of the board rather than a half. That is exactly why the roster shows you which lengths remain: as the fleet shrinks, your net can get coarser.

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Liked deducing a board a square at a time? Clear the mines in Minesweeper, draw a hidden picture from its number clues in Nonogram, or browse all games.