This really does look like some kind of modern art or maybe something your neighbor welded together in his backyard to make a little moonshine, but it’s actually a U.S.-made Mark IV, Model 1 naval mine dated April 17, 1917. It’s about three feet in diameter and held 300 pounds of TNT. I always thought they were set off by percussion, but this one was set off when the steel hull of a ship contacted it completing an electrical circuit with a copper wire antenna. That set off the firing battery followed by the detonator and Ka-Boom!
“Shooting Guns & Having Fun”