My buddy Brad was a explosive ordnance disposal specialist with the 51st EOD group (now disbanded) at Fort Sheridan, Illinois.  One day, the 51st duty office got a call from the surplus property disposal office at Navy Base, Great Lakes, Illinois, about 10 miles north.  Brad took the call and took the pickup truck to see what the property disposal people had found.  As it turned out, property disposal had a dummy 7.2-inch projector charge (also called a "Hedgehog") on their hands. 

 

The 7.2-inch projector charge resembled an oversized rifle grenade that was designed to attack submarines during World War 2.  The charge was 7.2 inches in diameter, about three feet long, weighed about 65 pounds, and carried a 29 pound charge of Torpex explosive detonated by a contact fuze.  Two 24-charge launchers were mounted on destroyers, destroyer escorts, frigates, or corvettes of the day.  Each launcher was retangular with a blast shield in back.  Inside the launcher were four rails that could positioned right or left to vary the pattern of the charges.  Each of the rails had six launching spigots.  The projector charge's tail boom was slid over the spigot.  When the launcher fired, an electrical voltage was sent through the firing pin to initiate the electric primer inside the tail boom; the primer fired the black powder impulse charge and blew the charge about 300 yards ahead of the ship.  Pairs of charges were fired from the spigots in 0.2 second intervals until all 24 were on their way to the target.  The charges were streamlined to sink rapidly and contact fuzed to explode on contact with the submarine.  If the Hedgehogs missed the submarine, sonar contact was not lost (as happened with the conventional depth charges of the period), the spigots were reloaded and the warship attacked the submarine again.

 

What property disposal had an inert, training Hedgehog on their hands.  The impulse charge had been removed and the explosive cavitiy in the warhead had been filled with concrete.  About the only danger was that it could tip over and crush someone's foot by accident.  After Brad had made his evaluation of the device, the property disposal office was relieved that they didn't have a live weapon in their midst.