'Marco Polo II', was transferred to the IJN at Kiel, commissioned as RO-501 and set sail under a Japanese crew, to rendezvous with I-8 to refuel, and proceed to Penang with precious metals, uncut optical glass, and blueprints and models for building Type IX U-boats and Messerschmitt Me 163 Komet rocket planes. She was intercepted and sunk west of the Cape Verde islands by USS Francis M. Robinson of the hunter-killer group on 13 May. On 5 December 1944 sailed from Bergen, Norway to deliver parts and plans for Me 262s and 1,857 flasks containing 65 tonnes of mercury under Operation Caesar. She ran aground and had to return to Bergen, which suffered a British bombing raid on 12 January 1945 that delayed repairs. U-864 sailed again on 6 February 1945, but was detected and sunk by the British submarine HMS Venturer in the Norwegian Sea in the action of 9 February 1945, the only time one submarine was sunk by another while submerged. In March 1945 sailed from Kristiansand for Japan with 1,210 tons of uranium oxide, an Me 262 jet fighter, and plans for new electric torpedoes, the last attempt to be made, but she was overtaken by the German surrender and was taken into custody by the USN off Newfoundland. Notes References External links Yanagi missions at history.net; retrieved 26 September 2018 Imperial Japanese Navy