The American Trick That Rebuilt Japan's Secret Cipher Machine Without Ever Seeing One in Person

In 1939, Japan's Foreign Ministry began sending its most secret diplomatic messages through a new cipher machine, the Type 97. The Americans called it Purple. No American had ever seen one. Yet by the end of 1940, a small US Army team in Washington had built their own working copy, out of ordinary telephone parts, using nothing but the enciphered messages themselves. The key breakthrough came on 20 September 1940, when mathematician Genevieve Grotjan spotted a pattern nobody else had seen. This is the story of how William Friedman, Frank Rowlett, Genevieve Grotjan and Leo Rosen rebuilt Purple, what it revealed about Hitler's plans through Japan's ambassador in Berlin, and why, despite everything it read, it still did not stop Pearl Harbor. Did someone in your family work as a codebreaker, a radio operator or a translator during the Second World War? Leave their name in the comments. ⏱ Chapters 0:00 A pattern on a worksheet 0:57 Tokyo's unbreakable machine 2:53 The Signal Intelligence Service 4:47 Trick #1: Study the messages, not the machine 5:56 Trick #2: Use the enemy's own habits 7:07 Trick #3: Look for the cycles 8:49 Trick #4: Build it from telephone parts 10:57 Trick #5: Share the machine, guard the secret 13:50 What Purple revealed: Oshima in Berlin 15:02 Honesty: why Purple did not stop Pearl Harbor 17:09 Why it worked 📚 Sources National Security Agency / Center for Cryptologic History — Purple and Magic National Cryptologic Museum — Purple machine fragment Frank Rowlett, The Story of Magic (memoir) David Kahn, The Codebreakers (1967) "Mr. Tanaka", the Japanese cipher officer in this video, is a composite character standing for the officials who trusted the Type 97 system. All other people and events are real. 🎞 Footage and images Photographs: Library of Congress, US National Archives, NSA and Wikimedia Commons (public domain). Purple machine and stepping-switch photos via Wikimedia Commons (CC BY-SA 2.5 / 4.0). Archive film: US National Archives (public domain). Stock video: Pixabay. #Purple #Codebreakers #WW2 #PearlHarbor #WW2History