Japanese Purple cipher
PURPLE was a Japanese cipher machine used during WWII and based off the Enigma's rotor technology. While it was developed in 1937 with four rotors (compared to the Enigma's three), it was broken only a few years later in 1940 without being seen by the successful cryptanalysts. William Friedman and the U.S. Signal Intelligence Service did this by building a working replica of the highest Japanese security code.
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Japan, “PURPLE,” Ciphers and Encryption, accessed September 26, 2021, https://crypto.omeka.net/items/show/6.