Fleet Logic Puzzles

Common questions

How do you solve a battleship puzzle?

Find where the fleet lies. The fleet list says how many ships there are and how long each one is, and the number beside each row and below each column says how many of its cells hold a ship. Ships lie in straight lines across or down, and no two ships touch, not even at a corner, so ship cells at row 1, column 1 and row 2, column 2 are flagged as touching diagonally. Given ship and water cells are fixed. Water marks are your own reminders for cells that cannot hold a ship; unmarked cells count as water. There is no separate submit step: the puzzle is solved the moment your ship marks meet every row and column total, no ship cells touch diagonally and the ships match the fleet. A row or column with a total of 0 is all water, and Fill forced water marks it for you.

Does every puzzle have exactly one solution?

Yes. For each seed the generator lays out a random fleet with no touching ships, counts the ship cells in every row and column and shows one of the ship cells as given. While another layout also fits those clues, one of that layout's ship cells that the intended layout leaves empty becomes given water, which rules the other layout out; then, while the step budget lasts, each given water cell is removed again if the puzzle stays unique without it. A separate solver that works cell by cell and does not know the intended answer must then prove exactly one solution within 200,000 steps before the puzzle is offered, and the page repeats that proof when the puzzle opens. A proof that reaches its step limit offers nothing: Generate from seed keeps the previous puzzle, and New puzzle moves on to the next seed, up to 16 seeds, but stops after three seeds that use up the whole generation budget. Each seed may try up to 48 candidate layouts within 2,000,000 steps. Steps are counted, not timed, so the same seed and fleet build the same puzzle on every device. Generation runs in a background worker that is stopped after eight seconds, keeping the previous puzzle; when workers are unavailable, the page generates the puzzle itself.

Can I choose the board size and the fleet?

Yes. Boards run from 6 × 6 to 10 × 10, and each size opens with its standard fleet: 3 2 2 1 1 1 on 6 × 6, 4 3 2 2 1 1 on 7 × 7, 4 3 3 2 2 1 1 1 on 8 × 8, 4 3 3 2 2 2 1 1 1 on 9 × 9 and 4 3 3 2 2 2 1 1 1 1 on 10 × 10. Choosing a size sets its standard fleet, and you can then type your own: ship lengths from 1 to 5 cells, up to 12 ships, separated by spaces or commas. A fleet that needs more room than the board has is refused before any search, and one that still cannot be placed without ships touching is refused with a message while the previous puzzle stays open. Only 6 × 6 puzzles with the fleet 3 2 2 1 1 1 can be shared as scored challenges.

How do ship marks, Fill forced water, hints and undo work?

Choose a tool, then tap a cell. With Cycle, one tap marks a ship, a second turns it to water and a third clears it; Ship and Water put their mark down or take it off again, and Clear empties the cell. Fill forced water marks water in every unmarked cell of a row or column that already holds its total, a total of 0 included, and in the corner neighbours of every ship cell, as one change that Undo removes; it never places a ship and is not treated as help. Undo and redo step through every change until the puzzle is solved; once every rule holds, the result is final, and Replay as practice starts the same puzzle again. Hint first corrects a mark that cannot be right, the selected cell first: a ship where water belongs becomes water, and water where a ship belongs becomes a ship. When every mark is right, it marks a ship of the solution in the selected cell if that cell holds one, otherwise in the first missing cell in reading order. Show mistakes highlights every ship or water mark that disagrees with the solution until the board changes, and Reveal solution shows the answer while keeping your own marks underneath. Hint, Show mistakes and Reveal solution turn the run into assisted practice. Rows and columns with too many ship cells or too few unmarked cells left, ship cells that touch diagonally, a ship longer than the longest in the fleet, more finished ships of one length than the fleet holds, and a board that meets every total with the wrong fleet are flagged from the rules alone, never from the answer. A ship counts as finished once every cell beside it is water, the board edge, or in a row or column that already holds its total.

How is the fleet puzzle challenge scored?

The challenge is one seeded original 6 × 6 puzzle with ships of 3, 2, 2, 1, 1 and 1 cells and one ship cell given. Score is 1000 minus your final retained ship placements, never below 0, and higher is better. The given ship cell is not a placement, so a clean solve marks nine ships and scores 991, the best possible. Every ship you put on a cell is a placement, including one put back after you cleared it or turned it to water. Water marks, Fill forced water, clears and taps that change nothing add no placement, and undo removes the undone placement. Hint, Show mistakes, Reveal solution, an answer key printed before finishing, restored progress, replays and puzzles already opened in this browser, including rotated or reflected copies, stay practice. Scores are self-reported.

What happens when someone opens a challenge link?

The page shows the shared score, the fixed rules and a Start same challenge button; nothing starts on its own, and the button is disabled once the shared attempt starts. The link carries only the seed, the board size setting and the claimed score, never marks or the answer, and the puzzle is regenerated from the seed. A link with a fractional, out-of-range, duplicated, wrong-size or wrong-tool value is refused with a message, and ordinary practice opens instead. After a fresh unassisted solve you see both scores, the signed difference and whether you did better, tied or scored lower, with Copy challenge link, Share challenge and Download result card for a new link that carries your score for the same puzzle. If the clipboard is refused, the full text appears in a box to copy by hand. Your earned score stays on the page when you replay or start another puzzle, until another scored solve replaces it.

Can I print a puzzle or come back to it later?

Print puzzle prints the grid with its row and column totals, the fleet and the given cells, without your marks or the solution. Print puzzle and answer key adds the ships on a separate page and, if you have not finished, turns the run into assisted practice. The print sheet leaves the page once printing ends. Once you make a change, progress is saved in this browser without the solution. On your next visit an unfinished puzzle reopens automatically, unless you arrive through a valid challenge link: it is regenerated from its seed and your history is replayed onto it, as practice. Every puzzle that opens is remembered in this browser right away, even one you never touch, so a reload cannot make it a fresh challenge. Saves keep up to 10,000 changes and remember up to 1,024 opened puzzles. If storage is unavailable, the puzzle stays playable in the open tab.

Can I play with a keyboard or on a phone?

Yes. Tap a cell to apply the chosen tool, or use the arrow keys and press S to place or remove a ship, W or X to place or remove water, and Backspace or Delete to clear. Mark selected cell, the move buttons and a selected-cell list give the same control without a keyboard. Every cell is at least 44 pixels, and on narrow screens every button and field is too; larger boards scroll inside their own frame on a phone instead of shrinking the cells. Each cell's accessible name includes its row, column, mark and whether it is given, and the page lists every row and column with its ship count, plus a text version of the board with the totals.