In 1940 he single-handedly deciphered and reverse-engineered an early version of the Siemens and Halske T52 also known as the Geheimfernschreiber (one of the "Fish cyphers") used by Nazi Germany, and created a device that enabled Sweden to decipher German teleprinter traffic passing through Sweden from Norway on a cable. In this way, Swedish authorities knew about Operation Barbarossa before it occurred.

Arne Beurling - Wikipedia, the free encyclopedia

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