This is not the Battleship you played with a friend on squared paper, firing shots at random and shouting “miss! hit!”. There is no opponent here and nothing to fire at: there is one grid, a fleet hidden inside it, and numbers along the edges. Your job is to work out where the ships are by reasoning, never by guessing.
It is the same pleasure as a cryptarithm or a Sudoku: every puzzle has exactly one possible arrangement, and every square can be deduced from the ones you have already settled. If you find yourself about to gamble, it means there is a deduction you haven't spotted yet — not that the puzzle is ambiguous.
The number at the start of a row tells you how many squares in that row are occupied by a ship. The same goes for the numbers above the columns. They don't say which squares, and they don't say how many ships: only how many squares in total. A 3 on a row could mean a whole cruiser, or a destroyer plus a submarine, or three separate submarines.
Below the grid every ship you have to find is drawn individually, with its shape: the battleship is 4 squares long, the cruiser 3, the destroyer 2 and the submarine 1. Knowing how many there are of each is part of the puzzle, and it is often the information that finishes it: once you have found all the long ships, whatever is left can only be short.
A shape in the list is only crossed off once that ship is closed: once you have marked water at both ends, or the ship runs into the edge. As long as one end still has an empty square next to it, the shape stays lit — even if the length already looks right. That is deliberate: a group of two squares could always be the trunk of a cruiser you haven't finished, and crossing off the destroyer would be telling you the ship ends there — a deduction that is yours to make.
The same thing happens on the grid, with colour: a closed ship turns orange, while trunks you might still extend stay grey. It is only a way of reading back at a glance what you have already worked out: the orange appears because you marked the water at the ends yourself, not because the game checked the solution.
Ships always lie straight, horizontally or vertically. Never diagonally, never bent into an L.
This is the rule that makes the puzzle solvable, and the one people forget most often. Every ship is surrounded by water on all sides: above, below, beside, and on all four diagonals. Two separate ships can never be in contact. Every time you find a ship square, you have automatically found that the four diagonal squares are water.
Left click marks a square as water. Right click marks it as ship. Clicking the same mark again clears the square. Squares with a gold border are given at the start: they are part of the puzzle statement and cannot be changed.
Marking water isn't required to win — only the ships need to be in the right place — but it is how the reasoning works: blacking out what is ruled out is exactly what makes it clear where the ships must be.
The edge numbers light up on their own: they turn green and dim once that row has all its ship squares, and red when the count can no longer work out (too many ships, or too few free squares left to reach it). This is pure arithmetic and never looks at the solution, so it stays on even with mistake flagging turned off.
If a row asks for 2 ship squares and you have already marked 2, everything else in that row is water. Obvious, but it is the deduction you'll use most, and blacking those squares out immediately unlocks the columns crossing them.
The row asks for 2 and both ship squares are there: the three highlighted squares must be water.
The reverse argument. If a row is 3 ship squares short and exactly 3 squares are still free, those are the ones. You don't need to know which ship it is: just mark them.
The row asks for 3 and the water has already ruled out two squares: the three free ones are all ship.
This follows straight from the no-touching rule. The moment you mark a ship square, the four diagonal squares are water — always, without looking at anything else. It is the most plentiful free information in the puzzle, and the game can fill it in for you with the option “Fill in the certain water automatically”, which also takes care of rows and columns whose count is already complete (deduction 1 above).
The four highlighted squares are water no matter what the numbers say.
Once a ship is complete — because you recognised it in the fleet list, or because the numbers leave no room to extend it — then its whole outline is water, not just the diagonals: the squares at each end too. Realising that a ship is finished is often the step that unlocks half the grid.
The cruiser is complete: all twelve squares around it are water.
At the start of a puzzle, always begin with the rows and columns marked 0: you can black them out in one go, without thinking. Then look at the highest numbers: if a 10-square row asks for 6, space is so tight that some squares are often occupied in every possible arrangement.
The kind of reasoning doesn't change between formats: what changes is how far you have to carry a chain before it closes.
The Hint button points at a square where a deduction is available, and costs +10 seconds on the clock. From there you can stop and think it through yourself, or ask for the Explanation (which tells you which of the deductions above applies) or have the game fill in the square: either one costs +20 seconds, once per hint.
If there is already a wrong mark on the grid, the hint points at that first: carrying on from a wrong premise only leads to a dead end.
With “Flag wrong squares right away” turned on, a mark that contradicts the solution turns red instantly and costs +30 seconds. The penalty is charged once per square: clearing it and marking it again doesn't stack up seconds. If you'd rather catch your own mistakes, turn the option off: the puzzle becomes more honest and the mistake counter stays at zero.
Time is the only score, penalties included. Best times are kept separately for each grid size — a 6×6 and a 10×10 aren't comparable — and split into today, this week (which restarts on Monday) and all time. The circular-arrow button resets the record above it: the first click asks for confirmation, so nothing gets wiped by accident.
Undo (or Ctrl+Z) steps back one mark at a time, all the way through the game. The H key asks for a hint. Penalties already charged are not refunded by undo: they are the price of a decision made.
If you close the page halfway through, next time the game offers it back with the Resume previous game button, clock included. The save lives in your browser, not on a server: clearing your browsing data clears it too.
The game ends the moment every ship square is in its place — you don't need to have blacked out all the water. If the grid looks full but something doesn't add up, the game tells you instead of leaving you to re-check everything.
© 2026 Luciano Manenti