Sea Battle is the classic guessing game of hidden fleets. Each player hides five ships on a 10×10 grid, then you take turns calling out shots at the other grid, trying to find and sink every ship before your own fleet goes down. It began as a pencil-and-paper game for two, and here it runs in your browser: play Sea Battle against the computer, or with a friend on one phone, tablet or laptop. A game takes ten to twenty minutes, is free to play, needs no account and works offline once the page has loaded.
How to play Sea Battle
- Each player has a 10×10 grid with columns A to J and rows 1 to 10, and a fleet of five ships: Carrier (5 cells), Cruiser (4), Frigate (3), Submarine (3) and Patrol boat (2).
- Place your fleet in secret. Ships lie across or down, stay inside the grid and never overlap. By default they may not touch, not even at a corner.
- Take turns firing one shot at a cell of the other grid, such as C7.
- A dot marks a miss and a cross marks a hit. When every cell of a ship has been hit, the ship is sunk and everyone is told which one.
- You cannot fire at the same cell twice, so every shot reveals something new.
- The first player to sink the whole enemy fleet wins.
The full rules, with the variants families often play, are in the Sea Battle rules guide.
Prefer to watch? See the 6-minute video on the Sea Battle rules page.
Play Sea Battle on one device
Choose With a friend to play two-player Sea Battle on a single screen. The game is built around hidden information, so a pass screen appears every time the device should change hands: before each of you places a fleet, and before every turn. It hides the board completely and waits for the named player to tap, so the other fleet stays secret even when you share a phone.
Placing a fleet is quick. Pick a ship, tap the grid to put it down, and press Rotate (or R on a keyboard) to turn it across or down. Tap another spot to move it, or press Random fleet to let the game place all five legally at once. Undo works while you are still arranging your own ships. When the fleet is set, press Ready and hand the device over.
During a turn the big grid is the enemy’s water with your shots on it, and your own fleet sits beside it as a small map showing every shot fired at you. After each shot you see the result for a moment, then the pass screen comes up for the other player. On a touch screen the first tap aims and a second tap (or Fire) shoots, so a slip of the finger never wastes a turn. With a keyboard, the arrow keys move around the grid and Enter fires.
Play against the computer
Choose vs Computer for a Sea Battle game on your own. Pick a level:
- Easy fires mostly at random and only sometimes follows up a hit. A good level for young players learning the game.
- Medium hunts in a checkerboard pattern and, after a hit, fires around it and along the line until the ship sinks.
- Hard works out every way the ships still afloat could be placed, given its hits and misses, and fires at the cell most likely to hold one.
The computer places its fleet at random and never peeks at yours: it plays only from the results of its own shots, just as you do. Rematch keeps the score and lets the other side start.
Quick tips
- Don’t fire at random. Every ship covers at least two cells, so searching every other cell, like the dark squares of a chessboard, finds every ship in half the shots.
- After a hit, try the four cells next to it. Once two hits line up, keep firing along that line until the ship is sunk.
- With the no-touching rule, the cells around a sunk ship are always water. Skip them.
- Hide your own ships in different parts of the grid and avoid predictable rows. Don’t crowd the edges either: an experienced opponent checks them.
- Keep count of the ships still afloat. If only the Patrol boat is left, the search pattern can be wider. If only the Carrier is left, a gap of four cells can’t hide it.
For worked examples of hunting, targeting and smart fleet placement, read the Sea Battle strategy tutorial. Looking for more games to share a screen with? Try Hangman, another guessing game with a secret to protect, or Dots and Boxes, a pencil-and-paper classic for two.