How to play
Sea Battle is a game of hidden ships and deduction for two players, here you against the computer. Each side hides five ships on its own 10×10 grid: a carrier of 5 squares, a cruiser of 4, a frigate and a submarine of 3 each and a patrol boat of 2, which makes 17 ship squares out of 100. Ships lie straight, across or down, and never overlap.
The players take turns firing at one square of the other grid. A shot is a miss (a dot), a hit (a cross) or, when the last square of a ship is hit, a sunk ship: the whole ship is outlined and named, so both sides know which one went down. Whoever sinks the entire enemy fleet first wins. You always fire first.
By default ships may not touch, not even at the corners, a rule used in many pencil-and-paper versions. The squares around a sunk ship are then certainly empty, and the game marks them with small rings for both sides. Tick Ships may touch each other for the looser rule of many boxed editions, or Shoot again after a hit for a popular house rule that gives a player another shot after every hit. The game itself is usually traced back to pencil-and-paper play around the time of the First World War.
Controls
- Mouse: drag a ship from the list onto your grid, or click a ship and then a square, which becomes the ship's front end (its top or left square). R or a right-click turns the selected ship, and clicking a placed ship twice turns it where it lies. Drag a ship off the grid to take it back, or let Random fleet place all five. In battle, click a square of Enemy waters to fire.
- Touch: tap a ship, then a square, or drag it. In battle the first tap aims, with the row and column highlighted, and a second tap on the same square or the Fire button shoots. On a small screen the Enemy waters and Your fleet buttons switch grids, and the game shows your fleet for each computer shot.
- Keyboard: the arrow keys move a cursor, Enter or Space places a ship or fires, 1 to 5 pick a ship, R turns it, Delete takes it off, A makes a random fleet, C clears and S starts the battle. H toggles the heat map, V switches the grid on small screens, N returns to the settings and F toggles full screen.
How the computer plays
Easy fires at random squares, skipping only squares already known to be empty. Normal hunts at random until it hits, then tries the four neighbours, and once it has two hits in a line it follows that line both ways until the ship sinks. Hard keeps a probability map: for every ship still afloat it counts every position where that ship could still lie, given all misses, hits, sunk ships and the touching rule. Each square scores the number of positions covering it, positions through earlier hits count many times more, and Hard fires at the top square. The Heat map button shows you this map for the enemy grid; a game won with it does not count for your best score.
Random shooting is slow because the last of the 17 ship squares tends to come late. If all 100 squares are fired at in random order, the last ship square is expected at position
17 × (100 + 1) / (17 + 1) ≈ 95.4.
In 2,000 simulated games per level against random fleets with the default rule, run on 22 October 2026, Easy needed 86.4 shots on average, Normal 50.2 and Hard 38.4. With touching allowed, Easy cannot skip any square and needed 95.3, close to the formula, Normal 59.7 and Hard 44.9.
Tips and strategy
- Hunt on a chequerboard pattern. Every ship covers at least two neighbouring squares, so firing only at squares of one chequerboard colour finds every ship with at most half the shots.
- After a hit, try the four neighbours; after two hits in a line, keep going along that line and turn around at a miss.
- Keep track of the ships still afloat. When only the carrier is left, a gap shorter than five squares cannot hide it.
- With the no-touch rule, the squares diagonally next to any hit are always empty, so never fire there.
- Try the heat map for a few turns to see why the centre comes first, then beat Hard without it.
Frequently asked questions
Can ships touch each other?
Not by default: there must be at least one empty square between ships, even diagonally. Tick Ships may touch each other on the start screen to allow ships side by side. The rule applies to both fleets.
Does the computer cheat?
No. Its shots are chosen only from the misses, hits and sunk ships on your grid, the same information you have about its grid.
How strong is Hard?
With the default rule Hard needs fewer than 40 shots on average, so beating it takes sharp hunting and some luck. Normal gives a fair fight, and Easy is good for learning the rules.
Sources
- Siegrist K (2022). 12.4: Order Statistics. Probability, Mathematical Statistics, and Stochastic Processes, LibreTexts. The mean of the largest of n numbers drawn without replacement from 1 to m is n(m + 1)/(n + 1); with n = 17 and m = 100 it gives the 95.4 above.