How to play Sea Battle

By Ari Hlynsson · 1 player vs computer, or 2 online · Updated 26 September 2026

Sink all five of your opponent's ships by calling out squares on their grid, before they sink all five of yours.

The two grids each player works with: their own fleet on the left, and the record of shots fired at the opponent's water on the right.

The rules, step by step

1
Lay out your fleet: one ship of five squares, one of four, two of three and one of two. Each sits in a straight line, across or down, and they may touch but never overlap.
2
You start with a legal layout already on the grid. Tap a ship to pick it, tap a square to move it there, and Rotate turns it. Shuffle deals a new arrangement.
3
Once both fleets are down, take turns firing. Tap one square on the enemy grid per turn.
4
A shot is a hit or a miss and is marked on the grid. One shot per turn either way, so a hit does not earn you another go.
5
When every square of a ship has been hit it sinks, and you are told which ship it was.
6
Sink all five of the other fleet to win. Your own grid, beside the target grid, shows where you have been hit.

Tips that change how you play

Fire on a diagonal lattice while you are searching. The smallest ship is two squares long, so it has to cover at least one square where the row and column numbers add up to an even number. Half the board is enough to find every ship.
Once you land a hit, finish the ship before you do anything else. Fire at the four squares around it until you get a second hit, then follow that line in both directions.
Keep track of which ships are left. Late on, if only the five-square ship is still afloat, there are very few places it can be, and any run of five clear squares is the whole search.

The three computer opponents

The three computer opponents
Level	How it searches	Shots to sink your fleet, on average
Easy	Fires at random squares, and may leave a ship it has hit alone.	95
Medium	Treats the grid as a chessboard and fires at one colour only, then finishes any ship it hits.	54
Hard	Counts every way the ships still afloat could lie, and fires where the most of them overlap.	44

Measured with the game's own code over 1,000 games per level against a fleet laid out at random, September 2026. Seventeen of the hundred squares hold a ship, so 17 shots is the fewest possible.

Finishing a ship the right way

Say you hit at E5 while sweeping the lattice. Do not fire at F6 next, however tempting the diagonal looks: ships do not run diagonally, so a diagonal shot tells you nothing about this one. Fire at E4. If that misses, fire at E6. If that misses too, the ship must be vertical, so it runs through D5 or F5 and you have only two candidates left. Suppose E6 hits instead. Now you know the ship is horizontal and at least two long, so keep going that way, E7 and then E8, until you miss. Then come back and try E4 for the other end. Four or five shots and the ship is down and identified. The same hit poked at from all sides with no plan can easily cost you eight.

Where to hide your fleet

The fleet you are handed at the start is laid out at random, and against the computer that is hard to improve on. The hard opponent fires first where the most ship positions overlap, and that is the middle of the board. A corner square can hold the five-square carrier two ways. A square near the centre can hold it ten ways, which is why its first shots land there.

The one layout that clearly helps the computer is ships packed together. Ships may touch, so one hit leads straight to the next ship. Five ships stacked in a corner lasted 31 shots on average against Hard and 33 against Medium. A random layout lasted 44 and 54. Keep them apart, and mix ships that run across with ships that run down, so one line of hits does not point to the others.

Searching faster as ships go down

Every ship you sink makes the search smaller. When a ship goes down, its squares turn solid red and its name is crossed off the fleet list. A lighter red hit left over belongs to a different ship. That happens often, because ships may touch, so finish that one next.

Then check what is still afloat. Once the two-square patrol boat is gone, every ship left is at least three long. You can switch from the chessboard pattern to every third square, a set of diagonal stripes that covers 34 squares of the hundred rather than 50 and still cannot miss a ship. A square boxed in by misses, where no ship still afloat could fit through it across or down, can be skipped altogether. The hard opponent works this out before every shot.

Mistakes that cost beginners the game

Firing at every square in order, or at random.: Both waste about half your shots. A lattice pattern finds every ship in roughly fifty calls instead of a hundred, and it costs you nothing to use, because no ship can hide between the squares you are skipping.
Wandering off after a hit to try somewhere more promising.: A wounded ship is the best information on the board and it does not stay useful. Finish it, learn which ship it was, and take that ship out of your reckoning for the rest of the game.
Bunching your own ships together.: Packed ships are the layout the computer sinks fastest, because ships may touch and one hit leads straight to the next. Spread the fleet out, and mix the orientations so that a vertical hit does not tell them everything.

Common questions about Sea Battle

Can ships touch each other?

Yes. Ships may sit side by side or end to end as long as they do not overlap, which is the classic rule. The variant that demands a clear square around every ship is a different game and is not offered here.

Do I get another shot after a hit?

No. One shot per turn, hit or miss. The bonus shot is a common house rule, but it compounds: a player who finds a ship first tends to find the rest before the other side gets going, and close games become rare.

Can the computer see where my ships are?

No. It is handed exactly the same information you are: the squares it has fired at, and which of its shots sank something. Its strength comes from working out which squares could still hold a ship, not from looking at your grid.

Who fires first?

A coin toss at the start of each game decides it, so sometimes the computer shoots first. Against another person online, the same toss decides who opens.

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