Select a tool, then click a cell.
Three enemy submarines are creeping toward your harbor. You can't see them — only sonar contacts, brief glimpses, and educated guesses. One action per turn. Sink all three before they slip past your blockade.
Three hidden enemy submarines are moving from the open sea (left) toward your harbor (right, green column). Sink all three before they reach it, or before the turn limit runs out.
Click any cell to ping it. You get a distance band to the nearest living submarine: Very Close (0-2 tiles), Close (3-5), or Far (6+). It never tells you direction — that's for you to triangulate over several turns.
Place a permanent buoy (limited stock). Every turn afterward, it automatically reveals the exact position of any submarine that enters its 1-tile radius — a passive tripwire.
Attack one cell outright. A hit sinks the sub instantly. A miss costs you the turn and a limited charge — commit carefully, based on the last known position and heading.
Reposition one of your 2 frigates up to 3 tiles. Frigates passively detect (fully reveal) any submarine that ends its move within 1 tile of them.
After your action, every surviving submarine moves — mostly toward the harbor, but they'll swerve to avoid your frigates and known buoys when they can. A detected submarine's position is shown for one turn only; after that it goes dark again.