How to Beat the Computer
The weaknesses of each difficulty's AI, and how to exploit them.
Casual fires randomly, so it takes a while. Any placement works fine against this opponent, making it a great chance to practice finding ships quickly with parity search on offense.
Skilled tracks the area around a hit and searches with a checkerboard pattern. Spread your ships apart so a single track can't expose more than one ship.
Admiral fires using probability density, making it extremely accurate. Avoid predictable placements, and use Auto Place to get a different arrangement every game to leave gaps in its calculations. On offense, targeting the center and longer ships first will raise your win rate too.