German submarine U-864 was a Type IX U-boat of Nazi Germany’s Kriegsmarine in World War II. She throughout her entire career under command by Korvettenkapitän Ralf-Reimar Wolfram departed from Kiel on 5 December 1944 on her 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 Venture , 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
According to decrypted intercepts of German naval communications with Japan, U-864 ’s mission was to transport military equipment to Japan destined for the Japanese military industry, a mission code-named Operation Caesar. The cargo included approximately 67 short tons (61 t) of metallic mercury in 1,857 32-kilogram (71 lb) steel flasks stored in her keel. That the mercury was contained in steel canisters was confirmed when one of the canisters containing mercury was located and brought to the surface during surveys of her wreck in 2005. Approximately 1,500 short tons (1,400 t) of mercury was purchased by the Japanese from Italy between 1942 and Italy’s surrender in September 1943. This had the highest priority for submarine shipment to Japan and was used in the manufacture of explosives, especially primers.
There was some speculation as to whether U-864 was carrying uranium oxide, as was U-234, which surrendered to the US Navy in the Atlantic on 15 May 1945, but Det Norske Veritas (DNV) concluded that there was no evidence that uranium oxide was on board U-864 when she departed Bergen. During the Norwegian Coastal Administration’s investigation of the wreck of U-864 in 2005, radiation measurements were made but no traces of uranium oxide were found.
According to her cargo list, U-864 also carried parts and engineering drawings for German jet fighter aircraft and other military supplies for Japan, while among her passengers were Messerschmitt engineers Rolf von Chlingensperg and Riclef Schomerus Japanese torpedo expert Tadao Yamoto, and Japanese fuel expert Toshio Nakai.
The shipwreck was located in March 2003 by the Royal Norwegian Navy 2 nmi (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, The plans to recover the submarine was estimated to cost 1 billion kroner (USD 153 million) and now the submarine will be covered with sand.