Probably made in Germany, my father was on a minesweeper working the east coast during WWII, their training was done in the Great Lakes so I doubt if it’s one of our training mines as one story suggest. They are deployed with an anchor and the mine floats up stoping at a preselected depth, I’m guessing this one didn’t float up or someone would have hit it by now After 70 years I guess some of the anchor hardware rusted thru and it floated away.