The following story appeared in the May 1997 issue of the Health Physics Society Newsletter. Unless otherwise noted, the details are from R.K. Wilcox’s "Japan’s Secret War", William Morrow and Company, NY, 1985. Additional information can be obtained by joining "Sharkhunters’ and utilizing their research archives. P.O. Box 1539, Hernando FL 34442
"The enemy shall find nothing but rats and mice in Germany—we shall never capitulate." The sign bearing these words looked on as U-234 glided out of the Kristiansand harbor. Evening, April 15, 1945.
U-234 was a type XB submarine, the largest class of German U-boat ever constructed. Of the eight that had been built, only U-234 and U-219 remained. The other six had paid a heavy price for their slow speed and lack of maneuverability (Helgason 1996).
Lieutenant Johann "Dynamite" Fehler, who had previously served on the infamous raider "Atlantis," was in command. In addition to his crew, Fehler was responsible for an important group of passengers: monocled Lieutenant General Ulrich Kesssler of the Luftwaffe; Colonels Sandrat and Neishling, also of the Luftwaffe; civilian rocket and jet experts; and most mysterious of all, Lieutenant Commanders Hideo Tomonaga and Genzo Shoji of the Imperial Japanese Navy.
Fehler’s mission: transport personnel and materials to Japan to support its war against the Allies. The final days of the Reich might be at hand, but what assistance could be provided Japan, would be provided. With a mission of such importance, Fehler had to avoid any possible contact with the enemy; U-234 ran deep and continuously submerged for two weeks after leaving Kristiansand. Only after making it through the English Channel into the Atlantic did Fehler feel sufficiently confident to surface for two hours each night
But events were at work beyond Fehler’s control. On May 10, the U-234 picked up a fatal shortwave transmission, Doenitz’s announcement of Germany’s surrender: "My U-boat men…you have fought like lions…lay down your arms." Instructions were given to proceed to the nearest allied port, but U-234 was so positioned that several possible destinations existed. Fehler decided to head to the United States. Unwilling to be captured, Hideo Tomonaga and Genzo Shoji committed suicide. On May 14, an American boarding party took over and directed the U-234 to Portsmouth, New Hampshire. Despite tight security, the arrival of U-234 at the docks became a major news event. Considerable coverage was devoted to the ship’s most illustrious passenger, Ulrich Kessler, e.g., "typical Hollywood version of a German general… as he strutted off the gangplank he casually looked around… and swaggered to a waiting bus. He wore a long leather great coat which reached to his ankles, highly polished leather boots and an Iron Cross." Much of U-234's top secret cargo, 240 tons of documents and war materials, was shipped to Washington and opened out of sight of the press’s cameras. A good deal was what might be expected, e.g., armor piercing antiaircraft shells. There were surprises, e.g., two Me-262 jet fighters. But, the biggest surprise of all came when 10 containers marked "Japanese Army" were opened. They contained 560 kg of uranium oxide!
Had the uranium reached its probable destinations, Osaka and the Riken Laboratory in Tokyo, enrichment via thermal diffusion might have been attempted.* Successfully enriched, the product would have been, by activity, mostly U-234!
Postscript: When General Groves, head of the U.S. atomic bomb effort, first learned of this submarine, it seems he was mistakenly informed that it was designated U-235, an idea that almost gave him "apoplexy."
Helgason, G. https://uboat.net/boats/u234.htm*Given the effort devoted to coordinating the shipment of so much uranium, this was probably the intention. However, a few days before the U-234 set out on its journey, the Riken Lab was destroyed by Allied bombing. What would have been done with the uranium had it reached Japan is unknown.
[Since this story was written, a substantial amount of new information has become available. Much of this can be found in the fascinating video, "U-234 - Hitler's Last U-boat." It seems possible, but by no means certain, that the captured uranium was sent to Oak Ridge and processed to help make the fuel for the atomic bomb dropped on Hiroshima.]