The Germans had no U235. They needed a reactor (pile) and due to a slight error thought graphite would not work; they were going to use a heavy water reactor (Deuterium).
The Allies blew up the German's only source of D2O, a Norwegian plant, then sank a passenger ferry carrying the last bits of D2O to Germany.
They had no isotope separation plant and only one cyclotron for cross-section work.
The Japanese had no nuclear program except for one or two people, and no equipment for serious isotope work.
It was heavy water that was on the sub, not 235. I think I remember now.
The History Channel claimed that they did. U.S. Naval personnel refused to off-load the U-235 from that captured Nazi submarine. They forced the Nazis to do the work themselves because the radiation levels scared them to death. HC showed films of the sub after it was captured. All these films, photos of Japanese planes, captured designs, and information was classified higher that Top Secret until recently. Go to the History Channel web site and do some digging.