Psychological warfare harassment weapon of WWII. A barrel sized device with a pipe on the top designed to look like a periscope, and cheap timing device to control flotation. The periboob was secretly placed in the enemy's busy shipping lanes, such as the entrance to strategic harbors, where it sunk to the bottom. Then at random intervals, would bob up, just below the surface, except for the protruding, ominious "periscope". The threatening periscope appeared ready to torpedo any surrounding vessels and required diversion of anti-submarine vessels from going after real submarines. Does no damage, except to morale, and the waste of resources.