#3: Encapsulated Metallic Mercury Drums (U-864)
The German U-boat U-864, sunk off Norway on February 9, 1945, carried a truly toxic cargo: 67 tons of liquid mercury in steel flasks. Realizing the ecological disaster that would follow if the corroding drums leaked, the Norwegian government made a difficult choice. Instead of attempting a risky recovery, they decided to entomb the entire wreck. The plan involves covering the submarine and its deadly cargo under a thick blanket of sand and gravel, sealing it away from the ocean for good.
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