This is a more difficult version of the game Battleship. You fire 5 shots at once and are only told how many of your shots hit. Your shots are grouped by turn (noted by the letters), and the number next to the letter tells you how many of the shots fired that turn hit. Click squares to fire. Press Z to dismiss a letter number pair. (irreversible) Press space to cycle a square's color.
Unfortunately you need to close your eyes while clicking the flag as the ships briefly show up.