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"On This Date in History" Calendar

1940: Purple Analog #1 Started Decryption

Wednesday, September 27, 2023

27 September 1940: On this day in 1940, PURPLE Analogue #1 started decrypting Japanese diplomatic communications. Frank B. Rowlett headed the team at the Army Signals Intelligence Service that broke the code. Genevieve Grotjan found the patterns required to wire the telephone switching units. Leo Rosen, the engineer on the team who had discovered that telephone switching devices were the answer for replicating the Japanese machine that he had never seen, built the Analogue (pictured here) and successfully tested it earlier this month.


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