Sea Battle

Before the first shot, each side places its fleet on its own grid: the Carrier (5 squares), the Dreadnought (4), the Cruiser (3), the Submarine (3) and the Destroyer (2). A ship lies in a straight line across or down — never diagonally — wholly inside the grid, and never shares a square with another. By default ships may not touch either, not even corner to corner.

Then the sides take turns firing one shot each at a square of the other's grid, named by its letter and number, such as E5. The owner answers miss or hit, and when the last square of a ship is hit, says which ship went down. On this page you always fire first, and a ship you sink surfaces on the enemy grid as a silhouette. Sink all five before the computer sinks yours and you win.

That depends on the rules agreed before the game. Many players let ships lie side by side; the version played in Russia, where the game is called Morskoy Boy — literally "sea battle" — forbids ships from touching at all, even at the corners. This page follows the no-touching rule by default, and the Ships may touch option in the ⋯ menu lifts it for both fleets.

The rule matters more than it looks. When ships may not touch, every sunk ship is surrounded by water nobody needs to search: a Destroyer sunk in open water rules out the 10 squares around it, a Carrier the 16 around it. That is worth about 7 shots a game to the Hard opponent on this page, which needs 38 shots on average to sink a fleet that may not touch and 45 when ships may.

Not at random. Firing blind, you would need about 95 shots on average to hit all 17 squares of a fleet, because the last ship tends to hide until the grid is nearly full. Three habits cut that nearly in half.

• Fire on a checkerboard. The smallest ship is two squares long, so every ship covers at least one square of each colour of a checkerboard. Firing only at the 50 squares of one colour cannot miss a whole ship. Once the Destroyer has sunk, the smallest ship left is three long, and every third diagonal — 34 squares — is enough.
• Favour the middle. On an empty grid each of the four centre squares can be covered by 34 different ship placements, and a corner by only 10. The middle is where a ship is likeliest to be.
• Finish what you hit. After a lone hit, try the four squares around it; once two hits line up, keep firing along that line until the ship sinks.

Like Minesweeper, it rewards counting rather than guessing: every miss removes placements, and the square that the most remaining placements cross is the best shot you have.

It fires using only what you would know in its place — its own hits and misses, and the ships it has sunk. It never looks at where your ships are, and the test suite checks exactly that: two different fleets that look the same from the shots so far always draw the same next shot. The three levels differ only in how they pick a square.

The averages are measured by the test suite over the same 150 randomly placed fleets, with ships not allowed to touch. In 100 full games played against each other, Hard beat Easy 99 times and Normal 91 times, and Normal beat Easy 87 times. Even the computer's choice between two equally good squares is drawn from the game's own number rather than from the clock, so a game played the same way twice unfolds shot for shot the same.

Once a day the computer's fleet is placed from the date instead of at random, so everyone who plays today's game hunts the same five ships and the number of shots you needed is a score worth comparing. Start it from the ⋯ menu, from the panel under the board, or from the daily games page.

A fleet that touches nowhere is legal under either rule, so today's fleet is always placed without touching, whichever options you play with. Your own fleet, and the extra-shot rule, stay yours to choose.

Nobody knows who invented it. It was a pencil-and-paper game, played on squared paper, long before it was a product: printed pads of grids were on sale in the 1930s, and a plastic pegboard edition followed in 1967. The name on this page is a plain translation of the Russian one, Morskoy Boy.

The Russian game uses a different fleet on the same 10 × 10 grid: ten ships — one of four squares, two of three, three of two and four single squares — none of which may touch. The five-ship fleet here, 17 squares from Carrier to Destroyer, is the one most English-speaking players grew up with.