Upon its arrival in the U.S., newspapers immediately reported on the unusual contents of the U-boat. There were French cognacs and 240 tonnes of weapon components for delivery to the Japanese ally. The most important part of the shipment, however, was 560 kg of uranium. As written on the U-boat manifest, the top-secret material was intended for the Japanese army.
Was there really uranium on board? If so, what happened to it? Was it used for one of the two nuclear bombs dropped in Japan? Historians have not been able to determine conclusively. In the archives of Portsmouth, the records have been lost.
A recent statement of John Lansdale, a former U.S. secret agent involved in the Manhattan Project (the top-secret US atomic-bomb project), has renewed speculation on the German U-boat's reported uranium shipment. Lansdale was responsible for Uranium Logistics in the Manhattan Project. The former head commander, now 84, recalled that the uranium was delivered directly to the nuclear-bomb complex in Oak Ridge: "The transportation papers passed over my desk at that time." His statement confirms the suspicion of many researchers. One of them, Vilma Hunt, an American nuclear expert and historian who worked on a book about the use of uranium in World War II, notes: "The builders of the atomic-bomb had at that time very little uranium to use. They scraped everything that they could get together, and used it in their atomic-bomb programme."
Within the very short period from the end of May to the end of July 1945, would it have been possible to extract four kg of the uranium-isotope 235 from the 560 kg of uranium? Difficult, but not impossible, if one takes into account that 150,000 persons were working on the project to construct the bomb.
Even if the four kg of U-235 had been extracted, it probably still would not have played a decisive role in the making of the U.S.' first atomic-bomb. In Little Boy (the bomb dropped on Hiroshima), about 60 kg of U-235 was used. Even without the German delivery, there would have been more than enough material for the necessary chain reaction. The German uranium could have been used in the two plutonium bombs: Trinity, tested in the New Mexico desert, and Fat-Man, dropped on Nagasaki three days after Hiroshima.
The U.S. military was alarmed when it discovered the uranium on the German U-boat. U.S. military officials feared that Japan was more advanced in its atomic-bomb program than they had earlier thought. The fear was unfounded. Only 50 scientists had worked on the nuclear bomb program in Tokyo. Even if the U-boat had made it to Tokyo, the uranium would not have made a considerable difference. The Japanese simply did not have the complex technology for uranium enrichment.