1942 1943 1944 1945 Associated articles Operation Caesar (Unternehmen Kaiser) was a secret mission carried out by Germany in the Second World War to supply Japan with advanced technology.

To counter the German U-boat, the Admiralty diverted the submarine HMS Venturer (Lieutenant James Launders), which had just left Lerwick in Scotland, to Fedje Island, off the coast of Norway to search for U-864.

Had it not been for the damage the U-boat sustained or the British bombing of Bergen, U-864 would have had a month's lead on Venturer by the time the Enigma code was broken and she was dispatched, which would have made a significant difference to the outcome.

After searching for five years, the U-boat was found in October 2003 by the mine control vessel HNoMS Tyr, 4 km (2.2 nmi; 2.5 mi) off Fedje.

The Norwegian government instead awarded a contract to a salvage company to raise the wreck but the proposed operation was postponed pending additional studies.

The Norwegian government spent 15 years assessing possible risks of raising the wreck, with its dangerous unexploded torpedoes inside.

Finally, in February 2017, it was decided to cover the U-864 with 50 centimetres of sand and 160,000 long tons (160,000 t) of rock to seal the mercury inside the wreck.