German submarine U-234

U-234 was one of the few U-boats that was fitted with a FuMO-61 Hohentwiel U-Radar Transmitter. This equipment was installed on the starboard side of the conning tower.

FuMO-61 Hohentwiel U-Radar Transmitter

U-234 was also fitted with the FuMB-26 Tunis antenna. The FuMB 26 Tunis combined the FuMB Ant. 24 Fliege and FuMB Ant. 25 Cuba II antennas. It could be mounted in either the Direction Finder Antenna Loop and separately on the bridge.

FuMB-26 Tunis Radar Detection

The cargo to be carried was determined by a special commission, the Marine Sonderdienst Ausland, established towards the end of 1944, at which time the submarine's officers were informed that they were to make a special voyage to Japan. When loading was completed, the submarine's officers estimated that they were carrying 240 tons of cargo plus sufficient diesel fuel and provisions for a six- to nine-month voyage.[3]

The cargo included technical drawings, examples of the newest electric torpedoes, one crated Me 262 jet aircraft, a Henschel Hs 293 glide bomb and what was later listed on the US Unloading Manifest as 550 kg (1,210 lb) of uranium oxide. In the 1997 book Hirschfeld, Wolfgang Hirschfeld reported that he saw about 50 lead cubes with 23 centimetres (9.1 in) sides, and "U-235" painted on each, loaded into the boat's cylindrical mine shafts. According to cable messages sent from the dockyard, these containers held "U-powder".[4][5]

When the cargo was loaded, U-234 carried out additional trials near Kiel, then returned to the northern German city where her passengers came aboard.

U-234 was carrying twelve passengers, including a German general, four German naval officers, civilian engineers and scientists and two Japanese naval officers. The German personnel included General Ulrich Kessler of the Luftwaffe, who was to take over Luftwaffe liaison duties in Tokyo; Kay Nieschling, a Naval Fleet Judge Advocate who was to rid the German diplomatic corps in Japan of the remnants of the Richard Sorge spy ring; Heinz Schlicke, a specialist in radar, infrared, and countermeasures and director of the Naval Test Fields in Kiel (later recruited by the US in Operation Paperclip); and August Bringewalde, who was in charge of Me 262 production at Messerschmitt.[5]

The Japanese passengers were Lieutenant Commander Hideo Tomonaga of the Imperial Japanese Navy, a naval architect and submarine designer who had come to Germany in 1943 on the Japanese submarine I-29, and Lieutenant Commander Shoji Genzo, an aircraft specialist and former naval attaché.[6]

U-234 sailed from Kiel for Kristiansand in Norway on the evening of 25 March 1945, accompanied by escort vessels and three Type XXIII coastal U-boats, arriving in Horten Naval Base two days later. The submersible spent the next eight days carrying out trials on her snorkel, during which she accidentally collided with a Type VIIC U-boat performing similar trials. Damage to both submarines was minor, and despite a diving and fuel oil tank being holed, U-234 was able to complete her trials. She then proceeded to Kristiansand, arriving on about 5 April, where she underwent repairs and replenished her provisions and fuel.

U-234 departed Kristiansand for Japan on 15 April 1945, running submerged at snorkel depth for the first 16 days, and surfacing after that only because her commander, Kapitänleutnant Johann-Heinrich Fehler, considered he was safe from attack on the surface in the prevailing severe storm. From then on, she spent two hours running on the surface by night, and the remainder of the time submerged. The voyage proceeded without incident. The first sign that world affairs were overtaking the voyage was when the Kriegsmarine's Goliath transmitter stopped transmitting, soon followed by the Nauen station. Fehler did not know it, but Germany's naval HQ had fallen into Allied hands.

Then, on 4 May, U-234 received a fragment of a broadcast from British and American radio stations announcing that Admiral Karl Dönitz had become Germany's head of state following the death of Adolf Hitler. U-234 surfaced on 10 May for better radio reception and received Dönitz's last order to the submarine force, ordering all U-boats to surface, hoist white flags and surrender to Allied forces. Fehler suspected a trick and managed to contact U-873, whose captain convinced him that the message was authentic.

At this point, the U-boat was almost equidistant from British, Canadian, and U.S. ports. Fehler decided not to continue his journey, and instead headed for the east coast of the United States. Fehler thought it likely that if they surrendered to Canadian or British forces, they would be imprisoned and it could be years before they were returned to Germany; he believed that the United States would probably just send them home.

Fehler consequently decided that he would surrender to U.S. forces, but radioed on 12 May that he intended to sail to Halifax, Nova Scotia, to surrender to ensure Canadian units would not reach him first. U-234 then set course for Newport News, Virginia. During the passage Fehler disposed of his Tunis radar detector, the new Kurier radio communication system, and all Enigma machine related documents and other classified papers. On learning that the U-boat was to surrender, the two Japanese passengers committed suicide by taking an overdose of Luminal, a barbiturate sedative and antiepileptic drug. They were buried at sea.[6]

A classified US intelligence summary written on 19 May listed U-234's cargo as including drawings, arms, medical supplies, instruments, lead, mercury, caffeine, steels, optical glass and brass.[8] That the ship carried 1,200 pounds (540 kg) of uranium oxide remained classified for the duration of the Cold War.[9] Author and historian Joseph M. Scalia claimed to have found a formerly secret cable at Portsmouth Navy Yard which stated that the uranium oxide had been stored in gold-lined cylinders rather than cubes as reported by Hirschfeld; the alleged document is discussed in Scalia's book Hitler's Terror Weapons. The exact characteristics of the uranium remain unknown; Scalia and historians Carl Boyd and Akihiko Yoshida have speculated that rather than being weapons-grade material it was instead intended for use as a catalyst in the production of synthetic methanol for aviation fuel.[4] However, after the war it was learned that the Japanese had cyclotrons and were working on the atomic bomb.[10]

The 1,200 pounds (540 kg) of uranium disappeared. It was most likely transferred to the Manhattan Project's Oak Ridge diffusion plant. The uranium oxide would have yielded approximately 7.7 pounds (3.5 kg) of ²³⁵U after processing, around 20% of what would have been required to arm a contemporary fission weapon.[11]

A torpedo from USS Greenfish sinks U-234 off Cape Cod, Massachusetts, in a 1947 training exercise.