Oct 14, 2026 · 27 min · 10 segments
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The cargo began as a request from Tokyo, and on July 7, 1943, Japanese Imperial Army headquarters instructed Hiroshi Oshima, Japan's ambassador in Berlin, to make a request.
He asked the Germans about exporting pitchblende, the ore uranium comes from, out of occupied Czechoslovakia.
The army's procurement chief, General Toranosuke Kawashima, later recalled that when he saw how little uranium a promising mine in Korea had produced, he wanted to cry.
The Germans wanted to know what the uranium was for, and Nishina didn't want to tell them.
He was working on isotope separation, and he assumed Germany wouldn't tolerate an ally competing in that field.
His assistant, Kunihiko Kigoshi, suggested a cover story, and in November 1943, it went to Berlin through official channels.
According to that narrative, Japan needed uranium oxide as a catalyst in the manufacture of butanol, which fed into aviation fuel production.
That actually worked, and late in 1943, Germany agreed to send uranium oxide east by submarine.
The first consignment left Kiel on March 30, 1944, aboard a former U-boat the Japanese had renamed Ro 501, and it went down with her in the Atlantic six weeks later.
What became of a second consignment has never been settled, though most historians don't believe it got to Japan because of what happened next.
In December 1944, Tokyo asked again, and by February 1945, they had 560 kilograms of uranium oxide waiting at Kiel and a submarine to put it in.
Her career started badly, and in May 1943, while she was still being built at the Germania yard in Kiel, an Allied bomb wrecked about 30 feet of her forward section.
Because of the delay, she wasn't commissioned until March 1944, after the result of the war was already a foregone conclusion.
That September, she went back into the yard to be rebuilt as a freighter, with a snorkel fitted and her mine shafts turned into cargo holds.
Her commander was Johann Heinrich Failer, a 34-year-old Berliner who had never taken a submarine into action.
He'd made his name as an officer on a commerce raider, where his work scuttling captured ships earned him the nickname Dynamite.
The same office decided what went aboard, and by the officer's own estimate, the boat carried 240 tons of cargo on top of fuel and provisions for a voyage of six to nine months.
The keel was said to be packed mostly with mercury and optical glass, and elsewhere went a crated Messerschmitt jet fighter alongside other high-tech German innovations.
Wolfgang Hirschfeld, the chief radio operator, later wrote in his memoir that the ten heavy cases were inspected and labeled by the two Japanese officers.
That label is the first of the story's problems, since U-235 is the rare isotope of uranium that sustains an explosive chain reaction.
The cargo began as a request from Tokyo, and on July 7, 1943, Japanese Imperial Army headquarters instructed Hiroshi Oshima, Japan's ambassador in Berlin, to make a request.
He asked the Germans about exporting pitchblende, the ore uranium comes from, out of occupied Czechoslovakia.
The army's procurement chief, General Toranosuke Kawashima, later recalled that when he saw how little uranium a promising mine in Korea had produced, he wanted to cry.
The Germans wanted to know what the uranium was for, and Nishina didn't want to tell them.
He was working on isotope separation, and he assumed Germany wouldn't tolerate an ally competing in that field.
His assistant, Kunihiko Kigoshi, suggested a cover story, and in November 1943, it went to Berlin through official channels.
According to that narrative, Japan needed uranium oxide as a catalyst in the manufacture of butanol, which fed into aviation fuel production.
That actually worked, and late in 1943, Germany agreed to send uranium oxide east by submarine.
The first consignment left Kiel on March 30, 1944, aboard a former U-boat the Japanese had renamed Ro 501, and it went down with her in the Atlantic six weeks later.
What became of a second consignment has never been settled, though most historians don't believe it got to Japan because of what happened next.
In December 1944, Tokyo asked again, and by February 1945, they had 560 kilograms of uranium oxide waiting at Kiel and a submarine to put it in.
Her career started badly, and in May 1943, while she was still being built at the Germania yard in Kiel, an Allied bomb wrecked about 30 feet of her forward section.
Because of the delay, she wasn't commissioned until March 1944, after the result of the war was already a foregone conclusion.
That September, she went back into the yard to be rebuilt as a freighter, with a snorkel fitted and her mine shafts turned into cargo holds.
Her commander was Johann Heinrich Failer, a 34-year-old Berliner who had never taken a submarine into action.
He'd made his name as an officer on a commerce raider, where his work scuttling captured ships earned him the nickname Dynamite.
The same office decided what went aboard, and by the officer's own estimate, the boat carried 240 tons of cargo on top of fuel and provisions for a voyage of six to nine months.
The keel was said to be packed mostly with mercury and optical glass, and elsewhere went a crated Messerschmitt jet fighter alongside other high-tech German innovations.
Wolfgang Hirschfeld, the chief radio operator, later wrote in his memoir that the ten heavy cases were inspected and labeled by the two Japanese officers.
That label is the first of the story's problems, since U-235 is the rare isotope of uranium that sustains an explosive chain reaction.
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