The Hoffman tank gunfire simulator is a device attached to a tank gun. It is made up of several fluted tubes, which create plumes of smoke, simulating qualities of firing a gun.
In early 2004, several Hoffman devices were reported as malfunctioning, and were recalled. These malfunctions included the devices discharging during maintenance, resulting in injury to personnel.
References
Hoffman tank gunfire simulator Wikipedia(Text) CC BY-SA