How to Play Sea Battle

Sea Battle is a game of hidden ships and good guesses that people have played with nothing more than squared paper and a pencil for over a hundred years. Many of us first played it in a school notebook, hiding the pages behind a raised arm, or on a rainy afternoon at the kitchen table. Two players each hide a small fleet on a grid, then take turns calling out squares, trying to find and sink the other side's ships first. This page explains the rules step by step, exactly as our free online Sea Battle game plays them.

What You Need

• Players: two. Online, you play against the computer.
• Paper: squared paper is easiest. Each player draws two grids, so it helps to sit where you can't see each other's page. A book stood on end works well as a screen.
• A pencil each, and an honest face.

The Grids

Each grid is a square of 10 by 10 squares, 100 in all. The columns are lettered A to J from left to right, and the rows are numbered 1 to 10 from top to bottom. Every square has a name made of its letter and its number: A1 is the top-left corner, J10 the bottom-right, and E5 sits near the middle.

Each player uses two grids:

• Your fleet, where you hide your own ships and mark the shots the other player fires at you.
• Your shots, a blank grid standing for the other player's sea, where you record where you have fired and what happened.

In our online game the two grids are labelled Your Fleet and Your Shots. On a computer or tablet they sit side by side; on a phone you see one at a time and switch with two big tabs.

The Fleet

Each player has the same five ships. Each ship takes up a straight line of squares:

So 17 of the 100 squares in each sea hold part of a ship, and 83 are open water. Families often use other names for the ships, and some play with a different fleet; the rule variations page covers the common ones.

Hiding Your Fleet

Before the first shot, each player secretly places all five ships on their own fleet grid. The rules for placing are simple:

• Each ship lies in a straight line, either across (along a row) or down (along a column). Never diagonally.
• Every square of a ship must be on the grid.
• Ships may not overlap: no square can hold two ships.
• In the standard rules, ships may touch each other, side by side or end to end. Many families play that they may not touch at all, not even at a corner; see ships touching.

Once the battle starts, ships never move. In our game you can press Place Them for Me and the computer hides your fleet in a random legal arrangement. You can also place each ship yourself: tap it in the list, then tap the square where its left end (or top end) should go. Turn switches between across and down. To move a ship, tap it on the board and then tap its new starting square.

Taking Turns

Players take turns firing. In our game you always fire first. On your turn you choose one square of the other player's sea and call it out: "E5". You can't fire at a square you have already tried; there is nothing new to learn there.

The other player looks at their fleet grid and answers truthfully, straight away:

• "Miss" if the square is open water.
• "Hit" if part of a ship is on that square.
• "You sank my cruiser" (or whichever ship it is) if that hit was the last undamaged square of the ship. A ship sinks when every one of its squares has been hit.

In the standard rules the answer to a plain hit does not say which ship was hit; you only find out the name when it sinks. Both players then mark the shot: the shooter on their shots grid (a dot for a miss, a cross for a hit), and the defender on their fleet grid so they can see the damage.

Our game does all the marking for you. A miss is a small dot, a hit is a bold X, and a sunk ship is outlined in heavy dark red, cross-hatched and labelled with its name. The most recent shot each side made gets a thick yellow frame so you never lose track of what just happened.

Winning

The first player to sink all five of the other player's ships wins. Since there are 17 ship squares, that means 17 hits. There are no points and no draws: someone always sinks the last ship first.

These figures come from many computer-played games on our site. They show how much a little method helps: the strategy guide explains how to search like the Hard computer.

A Worked Example

Suppose the computer has hidden its destroyer on F3, F4 and F5, running down column F. You know none of this, of course.

1. You fire at E5. "Miss." A dot goes on E5.
2. The computer fires at one of your squares; say it misses too.
3. You fire at F4. "Hit!" A bold X goes on F4. Some ship covers F4, but you don't know which one or which way it runs.
4. On your next turn you try a square beside the hit. G4: "Miss." Then F3: "Hit!" Now you have two hits in a row, F3 and F4, so the ship runs up and down column F.
5. You carry on along the line. F2: "Miss." So the ship can't extend upward; it must continue downward.
6. You fire at F5: "Hit, and you sank my destroyer!" The ship is three squares long, F3 to F5, and it is outlined and named on your board.

Notice how the misses helped: G4 told you the ship did not run across, and F2 told you which way to go. Each answer, even a miss, narrows down where the ships can be.

House Rules You Can Choose

Our game offers three common house rules in Settings. Each one has a fuller explanation on the variations page.

• A hit earns another shot. After a hit, the same player fires again, and keeps going until they miss. Games are faster and swingier.
• Salvo. Instead of one shot, you fire one shot for each of your ships still afloat, all at once, and then hear all the answers together. You start with five shots a turn and lose one with every ship you lose.
• Ships may not touch. No two ships may be next to each other, not even corner to corner. This applies to both fleets, and it gives a clever searcher extra information: the squares around a sunk ship must be empty.

Fair Play

On paper, the whole game depends on honest answers, and a mistaken "miss" can spoil a game for both players. It helps to read the square back ("E5... miss") before answering. Some families check both fleets at the end of the game, which also settles any arguments. Online, the computer can't make that mistake, and it can't peek: it decides where to fire using only its own shots and your answers, just as you do.

Quick Answers

Can I fire at the same square twice?

No. It would tell you nothing new, so the game doesn't allow it.

Do I have to say which ship was hit?

Not in the standard rules. You only name a ship when it sinks. Some families announce the ship on every hit; it makes the game a little easier.

Who goes first?

On paper, toss a coin or let the youngest start. In our game you always fire first. That is a small head start, worth about one shot.

Ready to give it a try? Head to the Sea Battle game. If you enjoy a quiet game of logic and deduction, you might also like Minesweeper, and for another classic two-player board game, try Reversi.