RIKEN, the Ni-Go Project (lit. "The Second Project"). Its aim was to separate uranium-235 by thermal diffusion, ignoring alternative methods such as electromagnetic separation, gaseous diffusion, and centrifugal separation. By Spring 1944, the Nishina Project barely made any progress due to insufficient uranium hexafluoride for its Clusius tube. The previously provided uranium within the copper tube had corroded and the project was unable to separate U-235 isotopes. By February 1945, a small group of scientists had succeeded in producing a small amount of material in a rudimentary separator in the RIKEN complex—material which RIKEN's cyclotron indicated was not uranium-235. The separator project came to an end in March 1945, when the building housing it was destroyed by a fire caused by the USAAF's Operation Meetinghouse raid on Tokyo. No attempt was made to build a uranium pile; heavy water was unavailable, but Takeuchi Masa, who was in charge of Nishina's separator, calculated that light water would suffice if the uranium could be enriched to 5–10% uranium-235. While these experiments were in progress, the Army and Navy searched for uranium ore, in locations ranging from Fukushima Prefecture to Korea, China, and Burma. The Japanese also requested materials from their German allies and of unprocessed uranium oxide was dispatched to Japan in April 1945 aboard the submarine , which however surrendered to US forces in the Atlantic following Germany's surrender. The uranium oxide was reportedly labeled as "U-235", which may have been a mislabeling of the submarine's name and its exact characteristics remain unknown; some sources believe that it was not weapons-grade material and was intended for use as a catalyst in the production of synthetic methanol to be used for aviation fuel. The attack also effectively destroyed the Clusius tube and any chances of the Japanese producing an atomic bomb in time to influence the war in their favor and rival the West in nuclear weaponry. According to the historian Williams, "The same lack of sufficient high quality uranium that had impeded the German atomic project had also, as it turned out, obstructed Japanese attempts to make a bomb." This was the conclusion of the Manhattan Project Intelligence Group, who also reported Japan's nuclear physicists were just as good as those from other nations. F-Go Project In 1943 a different Japanese naval command began a nuclear research program, the F-Go Project (lit. "The F Project"), under Bunsaku Arakatsu at the Imperial