Sea Battle is a two-player game of hidden ships and called shots. Each player secretly arranges a small fleet on a square grid, and the players take turns naming cells on the other grid to fire at. The defender answers honestly with a miss, a hit, or a sunk ship. Nobody ever sees the other fleet until the end, so the game is all about reading the answers and narrowing down where the ships must be. This guide covers the rules played on this site, the reasons behind them, and the variants you are likely to meet at home or at school.
Watch: how to play Sea Battle
How to Play Sea Battle: Rules Explained Simply
Chapters
Overview
The game was first played with pencil and squared paper, which is why it still uses a grid with letters and numbers. You need two grids per player: your ocean, where your own ships are drawn, and your target grid, where you record the shots you fire at the other player. On a screen, the game keeps both for you.
The rules on this site use a 10×10 grid, a fleet of five ships and one shot per turn. As in many pencil-and-paper versions, ships may not touch and a hit is announced as a plain hit; the boxed edition lets ships touch and names the ship on every hit. Two options let you allow touching ships and an extra shot after a hit.
The grid
Each grid has 10 columns, labeled A to J from left to right, and 10 rows, numbered 1 to 10 from top to bottom. A cell is named by its column and row: A1 is the top left corner, J10 the bottom right, and E5 sits near the middle. Using the same names on both sides is what makes calling shots possible, so check that everyone reads the grid the same way before the first game.
The fleet
Every player has the same five ships:
| Ship | Length |
|---|---|
| Carrier | 5 cells |
| Cruiser | 4 cells |
| Frigate | 3 cells |
| Submarine | 3 cells |
| Patrol boat | 2 cells |
That makes 17 cells of ships on a grid of 100, so about one cell in six holds a ship. The names are just labels; what matters is the length, because it is what each player announces when a ship sinks.
Placing your fleet
Before any shots are fired, both players place their fleets in secret. The placement rules are:
- Straight lines only. A ship covers a row of neighboring cells either across (along a row) or down (along a column). No diagonals, no bends.
- Inside the grid. Every cell of every ship must be on the grid.
- No overlapping. Two ships can never share a cell.
- No touching. In this site’s default rules, as in many paper versions, ships may not touch each other, not even at a corner. Each ship is surrounded by water on every side.
- No moving later. Once the game starts, the fleet stays where it is until the end.
The no-touching rule makes the game easier to follow: when a ship sinks, everyone knows that the cells around it are water. The boxed edition has no such rule, and many families play without it. On this site, turn on Ships may touch to allow ships to lie side by side or end to end. Overlapping is never allowed.
On this site, you place ships by picking one and tapping the grid; the tapped cell becomes the ship’s top or left end. Rotate turns the ship you are holding, Random fleet places all five legally in one go, and Ready locks the fleet once every ship is on the grid. The game refuses a placement that breaks a rule and tells you why.
Objective
Sink all five ships of the other fleet before the other player sinks yours. There are no points for near misses and no draws: the first player to hit every cell of every enemy ship wins.
Taking turns
Decide who goes first; on this site, it is part of the setup. Then the players alternate. On your turn:
- Choose a target cell on the other grid that you have not fired at before.
- Call it out, for example “F6”.
- The defender answers with the result: miss, hit, or sunk.
- Mark the result on your target grid. The defender marks the shot on their own ocean.
Then it is the other player’s turn. In the standard game every turn is exactly one shot, whatever the result.
Hits, misses and sinking
- Miss. The cell is empty water. On paper it is usually marked with a dot or a small circle; on this site it is a dot.
- Hit. The cell holds part of a ship. On paper it is marked with a cross; on this site it is a cross on a red tile. Here, as in many paper versions, the defender does not say which ship was hit; the boxed edition names it on every hit.
- Sunk. When the last cell of a ship is hit, the defender says so and names the ship, for example “You sank my Cruiser”. On this site the sunk ship is drawn whole, in a dark shade with a cross on every cell, and the roster beside the board strikes it out.
Answers must always be honest. The whole game depends on it, so on paper it helps to read back each shot (“F6, miss”) and to let the defender check their own ocean before answering. On a screen, the answers are given automatically.
Winning
The game ends at once when the last ship of a fleet is sunk. The player who fired that shot wins. On this site, the result shows how many shots each player needed and how many of them were hits, and when you lose against the computer, its remaining ships are revealed on the grid.
Playing on one device
On paper, the two players simply hide their grids behind a book or a box lid. When you share a phone or a tablet, the game does the hiding for you. With With a friend selected, a pass screen covers the whole board before each player places a fleet and before every turn. It names the player who should take the device and waits for them to confirm. The other fleet is never drawn on the screen, and the announcements read out by screen readers only describe shots and results, never where a hidden ship lies.
During your turn you see the enemy’s water with your own shots, and a small map of your fleet with the other player’s shots. After you fire, the result stays on screen for a moment so you can see it, and then the pass screen hands the device over.
Undo is only available while you are arranging your own fleet. Once shots are fired, both players have seen their results, so taking one back would not be fair.
Variants and house rules
Extra shot after a hit. A hit earns another shot, and a turn only ends with a miss. Games become faster and swingier, and a lucky streak can sink a ship in a single turn. Turn it on with Extra shot after a hit.
Ships may touch. Ships may lie side by side or end to end, as in the boxed edition, which only forbids overlapping. Finishing a ship tells you less, because the water around it is no longer guaranteed. A row of hits might even belong to two different ships. Turn it on with Ships may touch.
Salvo. Each player fires several shots per turn, often one per ship still afloat, and hears the results only after the whole volley. This version rewards careful bookkeeping and is best on paper.
Name every hit. The defender says which ship was hit each time, not only when it sinks. This is the rule of the boxed edition. Knowing the ship makes the game shorter and easier, which also suits younger players.
Other fleets and grids. Older paper versions use more ships, such as one of 4 cells, two of 3, three of 2 and four single cells, often with the no-touching rule. Smaller grids such as 8×8 make shorter games. Whatever you choose, both players must use the same fleet and the same grid.
Tips for fair games on paper
- Draw both grids before you start and label the rows and columns clearly.
- Place your ships in pencil and check every rule before the first shot. A ship that turns out to be illegal halfway through usually ends the game in a dispute.
- Mark every shot you fire on your target grid, misses included, and every shot you receive on your ocean.
- Say results out loud and in full: “C4, hit.” Mumbled answers cause most disagreements.
Common mistakes and disputes
- Forgetting to announce a sinking. The shooter then keeps firing around a ship that is already gone. Always say when a ship sinks and which one.
- Reading the grid the wrong way round. One player counts rows from the bottom, the other from the top. Agree on A1 before you start.
- Moving a ship. Ships cannot move once the first shot is fired, even if the owner forgot a rule. If a placement was illegal, the fair fix is to start again.
- Firing twice at the same cell. On paper the second shot is wasted. Mark every shot to avoid it.
Glossary
- Ocean: your own grid, with your ships.
- Target grid: the grid where you record your shots at the other fleet.
- Miss: a shot into empty water.
- Hit: a shot that lands on a ship.
- Sunk: a ship with every cell hit.
- Hunting: searching for a ship you have not found yet.
- Targeting: firing around a hit to finish the ship.
- Parity: searching every other cell, because every ship is at least two cells long.
Play it now
Ready to try it? Play Sea Battle against the computer or with a friend on one device. To get better at finding ships, read the Sea Battle strategy tutorial, which covers hunting patterns, targeting after a hit and where to hide your own fleet.