Sea Battle

Two grids, ten squares by ten. You hide five ships on yours, the other side hides five on theirs, and then you take turns calling squares until one fleet is gone. Neither of you can see the other grid, so every shot is a question and every answer narrows the board.

Laying out a fleet on a phone is the part that usually goes wrong, so you are handed a legal layout before you are asked for one. Tap Start firing and play. Or pick a ship, tap where you want it, rotate it, and shuffle the whole arrangement if you would rather not think about it.

One shot a turn, hit or miss. The bonus shot for a hit is a house rule and it is not used here, because it compounds: whoever finds a ship first tends to find the rest before the other side gets going. Three strengths of opponent. Easy fires blindly. Medium hunts on a lattice and finishes what it wounds. Hard works out which squares could still hold a ship at all, and fires at the likeliest one.