There has been speculation as to why the two Japanese officers aboard U-234, bound for Tokyo, decided to take their lives when the Skipper, KAPITANLEUTNANT JOHANN-HEINRICH FEHLER (32-+-1984) headed instead for the coast of the United States after receiving the surrender order from GrossAdmiral Karl Donitz. Here is a letter from YOYA KAWAMURA (1739-LIFE-1991), and he writes:

“There is absolutely no doubt that, as a Japanese officer, CDR Tomonaga could never permit himself to be taken prisoner by the Americans. Japanese servicemen were explicitly forbidden by the Military Code to surrender to the enemy under any circumstances. But, at the same time, Tomonaga was in possession of some secrets that had to be guarded at any cost.

Above all, he was the inventor of two very important, top-secret devices related to the submarine. One was SENSUIKAN JIDO KENCHO SOCHI (submarine automatic hanging device) which made it possible for a submarine to stay submerged without running its electric motors almost indefinitely. The other was SENSUIKAN JUYU ROEI BOSHI SOCHI (submarine fuel leakage prevention device) which prevented the leakage of fuel out of the tank ruptured by depth-charge attacks. Those two devices were being successfully used by Japanese submarines. One of the reasons Tomonaga was sent to Germany was to teach the Germans how to build and use these secret devices.”

How did these secret devices work?