Retrograde Battleships is a variant of Battleships, where the ships given must be located within the grid.
The objective is to add ships to the grid, subject to the following rules:
- All given ships on the in the key must be included in the grid with no others.
- The grid contains possible placements for all ships, the correct locations of the ships needs shading in.
- No ship may touch another, even diagonally.
A standard 10x10 retrograde battleships and its solution.