This game requires a 9 V battery.
The players are destroyers chasing after a computer-run submarine. The players plot the movements of their ships and the sub using crayons on the erasable board. Although the players co-operate, the winner is the one to actually sink the sub. The computer knows all about the ships (their movements are entered in to it) and the sub, but the players initially only know the sub's range by taking sonar readings. In this game, a sonar reading constitutes a square (not a circle!) centered on a ship (range is measured diagonally+vertically or diagonally+horizontally but never horizontally+vertically).
The sub moves at a steady speed and direction each time a player takes a turn. The sequence goes like this:
a) Ship 1 gets and plots a sonar reading.
b) Ship 1 moves and plots its movement.
c) Ship 1 gets and plots another sonar reading.
d) Sub moves one square.
e) Ship 2 gets and plots a sonar reading.
and so on. After a few turns, the sub's position and heading should become known from studying the sonar readings plotted on the board. However, its depth is as yet unknown -- for it can be at any one of three possible values. Now each player gets to aim and fire depth charges in addition to moving (if within 2 squares of the sub). This is done without telling the other players the result, so each player must discover the depth on his or her own. The sub may fire back at the ship, knocking it off course. Hitting the sub ends the game.