Aut cum scuto aut in scuto
To Russia...with love.
Those things kept Taking Out Ships well into the 1960's, until they Rusted and Sank...
My old man was working a rig in the north Atlantic during the mid to late seventies. Had to get the British royal navy to deal with a WWII mine adrift in the area.
for the least amount of money and time and risk with the most persistence, damage caused and area denial. planted just far enough apart to prevent fratricide and at a depth just below low tide on the outside ring with floater on the inside will give many a ships captain pause to reflect on the virtues of conservative actions.