sink all 3 enemy subs before they sink yours.
tap the enemy sea to fire. a miss echoes: the number is how far the nearest enemy contact is. diagonals count.
1 hot 2 warm 3 cool · cold (4+)
decoys echo like subs. shoot one and it pops. hide yours where they'll waste shots.
sonar, once per game, scans a 3×3 area. subs and decoys look the same on it.