Sea Battle Strategy: How to Win More Games

Sea Battle looks like pure luck, and the first shot of a game really is a guess. But after that, every answer tells you something, and a player who uses that information well needs far fewer shots than one who doesn't. On our site, a computer firing at random needs about 95 shots to sink a fleet; our Hard computer, which follows the ideas below, needs about 45. This guide explains those ideas in plain terms. If you are new to the game, start with the rules.

1. Search in a Checkerboard Pattern

Imagine the grid colored like a checkerboard. The smallest ship, the patrol boat, covers two squares side by side, and any two neighbouring squares are always one light and one dark. So every ship, whatever its size and wherever it lies, covers at least one "dark" square. That means you only need to search the dark squares, half the grid, to be certain of finding every ship.

Once the patrol boat is sunk, you can space your search out even more. If the smallest ship left is three squares long, firing at every third square along each row (shifting the pattern by one on each new row) is enough to cross every remaining ship. Our Hard computer does exactly this, and its Why? explanation will say when a square is "on the checkerboard pattern".

2. Aim Where Ships Fit in the Most Ways

Not all squares are equally likely to hold a ship. A corner square can only be covered by a ship lying along one of two edges, while a square in the middle can be crossed by a ship in many more ways, from the left, from the right, from above and from below. Early in the game, the middle squares are simply better bets.

As the game goes on, misses change the picture. A square hemmed in by misses on all sides can't hold a ship at all: there is no room. A long gap between misses can hold the carrier, while a two-square gap can hold only the patrol boat, and if the patrol boat is already sunk, that gap is empty water and you can ignore it.

Good players do a rough version of this in their heads: "Where could the carrier still fit?" The Hard computer does it exactly. For every ship still afloat, it counts every position that fits around the misses and sunk ships, adds them up square by square, and fires where the count is highest. It's a "heat map" of the likeliest squares, and the Hint button in our game gives you the same advice, with the count.

3. After a Hit, Finish the Job

A hit changes everything. Stop searching and work on that ship until it sinks:

1. Try the four squares beside the hit: above, below, left and right. The ship must continue in one of those directions.
2. Once you have two hits in a row, you know which way the ship runs. Carry on along that line in both directions until you get a miss at each end, or the ship sinks.
3. Pick the side with more room first. If a hit is one square from the edge, the ship is more likely to run inward, where there is space for it.
4. Watch for two ships side by side. If you have three hits in a row and the ship that sinks is only two long, the extra hit belongs to another ship. Go back and finish that one too.

Our Normal computer plays this way. The Hard computer goes a step further and asks which neighbouring square the damaged ship could reach in the most ways.

4. Count the Ships That Are Left

The list of enemy ships under your board is a powerful clue. Suppose only the carrier and the cruiser remain. Then any gap of three squares or fewer, across and down, is empty, and you never need to fire into it. Late in the game this can cut the number of squares worth trying to a handful.

5. Hide Your Own Fleet Well

Finding ships is only half the game. A few habits make your fleet harder to sink:

• Avoid patterns. All ships in neat rows, or all along the edges, are easy to guess once one is found. Mix across and down.
• Don't always hug the edges. Edges feel safe because fewer positions cross them, and a careful searcher fires there less early on. But a computer that counts positions will get there in the end, and a human who knows your habit will go there first.
• Touching ships can confuse. When touching is allowed, two ships side by side make the other player think one ship is longer than it is. With the no-touching house rule, every sunk ship leaves a ring of empty water, which helps the searcher, so spread out and keep your ships hard to box in.
• Vary it. The computer doesn't learn your habits from game to game, but human opponents do.

In fact, against a careful searcher no hiding place is truly safe, and Place Them for Me gives you a perfectly random fleet, which is as hard to read as any.

6. Salvo Games

In a salvo game you fire several shots at once and only then hear the answers. A few things change:

• Spread your salvo out while searching. Shots close together tend to find the same ship. Spread out, each on the checkerboard pattern, to cover more water.
• After a hit, surround it. With four or five shots you can try all four neighbours of a hit in one turn, and use the rest to keep searching.
• Protect your fleet. Every ship you lose costs you a shot per turn, so a lost ship hurts twice. Sinking the other side's ships early, even the small ones, cuts their firepower.

7. The "Extra Shot" House Rule

When a hit earns another shot, finishing off a damaged ship becomes even more valuable, because each hit lets you keep firing. Follow your hits carefully: a well-aimed run can sink a whole ship in one turn.

Ready to put this into practice? Play Sea Battle now, or look at the rule variations. If you like games of careful deduction, try Minesweeper too.