German Submarine U-864

German Submarine U-864

German submarine U-864 was a German Type IX U-boat of World War II. It departed from Kiel on 5 December 1944 on its last mission, to transport to Japan a large quantity of mercury and parts and engineering drawings for German jet fighters. While returning to Bergen, Norway to repair a misfiring engine, U-864 was detected and sunk on 9 February 1945 by the British submarine HMS Venturer, killing all 73 on board. It is the only instance in the history of naval warfare where one submarine intentionally sank another while both were submerged.

The shipwreck was located in March 2003 by the Royal Norwegian Navy 2 nautical miles (3.7 km; 2.3 mi) west of the island of Fedje in the North Sea, at 150 metres (500 ft). The mercury had been seeping out of rusted containers, contaminating the region and sea life. One study recommended entombing the wreck under a layer of sand as well as gravel and concrete. The Norwegian government instead awarded a contract to a salvage company to raise the wreck; however, the proposed operation has been put on hold pending additional studies.