Battleship stopped being a guessing game for me the day I understood one thing: because every ship covers at least two cells, you only ever need to search half the board.
What I cover
1. Fire on one checkerboard colour only
This is the single biggest efficiency upgrade in the game, so start here. Picture the ten by ten grid as a checkerboard of alternating colours. Every ship in the fleet spans at least two cells, which means no ship can fit entirely inside cells of one colour. So if you fire only at cells of one colour, you still touch every possible ship position on the board.
The effect is that you have halved your search space at no cost whatsoever. Fifty candidate cells instead of a hundred, with exactly the same guarantee of finding every ship. Your hit rate during the hunting phase roughly doubles the moment you start doing this deliberately.
2. Switch to target mode the instant you hit
Hunting and targeting are two different jobs and you should treat them that way. While hunting you are spreading shots on parity cells looking for anything. The moment you land a hit, stop hunting and start finishing that ship.
Probe the four neighbours of your hit to find the ship's orientation, then push along that axis until the ship sinks or you miss at both ends. Going back to parity firing while a wounded ship sits on the board is the most common way to waste turns, because you already know exactly where to look.
3. Spread your own fleet, do not hide it cleverly
Most players try to hide individual ships in unlikely places. That is the wrong problem to solve. The computer opponent here hunts with parity like a good human, so no single cell is meaningfully safer than another during its hunting phase.
What actually costs you games is clustering. Once the opponent gets a hit and starts probing outward, an adjacent ship is likely to be found by accident, so clustered fleets can cost you two ships for one discovery. Spreading the fleet across the board means each discovery buys the opponent exactly one ship and nothing more.
4. Use the board edges without hugging them
Edges and corners have fewer possible ship orientations passing through them, which cuts both ways. A ship placed hard against an edge is in a slightly less likely position from a pure probability view, which is a small advantage. But an edge also constrains where the rest of that ship can be once one cell is hit, which makes it faster to finish off.
The practical answer is to use edges for your shorter ships, where the constraint matters less, and keep the carrier away from the outer ring so that a single hit does not immediately tell your opponent which way it runs.
5. Use Shuffle properly before you start
This version uses shuffle-to-taste placement: you tap Shuffle until the random layout suits your strategy, then start. That is veto power, and most players do not use it. It keeps setup fast on a phone while still letting you reject any layout you do not like.
What to reject: anything where two or more ships sit adjacent or diagonally touching, and anything where three ships cluster in one quadrant. What to accept: a layout with ships in at least three different quadrants and no two hulls touching. Two or three taps usually gets you there.
6. Keep a mental map of what you have ruled out
Every miss is information. Once you have missed on a parity cell, you know no ship occupies it, which constrains where the remaining ships can fit. Late in a game, that accumulated information often narrows the destroyer down to a handful of possible positions.
This matters most for the two-cell destroyer, which is the hardest ship to find and the one people waste the most shots on. Rather than continuing to fire randomly, look for the remaining gaps large enough to hold two adjacent cells. Usually there are far fewer than you would guess, and one of them has the ship in it.
If you want the wider background, the Battleship entry on Wikipedia covers the game's history and the maths behind optimal search.
FAQ
What is parity firing in Battleship?
Firing only at cells of one colour on an imaginary checkerboard. Because every ship covers at least two cells, no ship can hide entirely within one colour, so half the board is enough to guarantee finding every ship. It halves your search space at no cost.
Should I keep using parity after I get a hit?
No. Once you have a hit, switch to target mode and probe all four neighbours regardless of colour to find the ship's direction, then push along that axis until it sinks.
Where should I place my ships?
Spread out, with no two hulls touching by edge or corner, and ships in at least three different quadrants. Clustering is what costs games, because one probe can find two ships.
How do I find the last two-cell ship?
Use your misses. Every miss rules out a cell, so late in a game only a handful of gaps remain that are large enough to hold two adjacent cells. Fire into those rather than continuing at random.