"On This Date in History" Calendar
1939: Japanese first use of PURPLE
20 February 1939: The Japanese first use of the PURPLE machine-generated diplomatic cryptosystem.
PURPLE was the codename Americans gave an Imperial Japanese Navy diplomatic cipher used to send messages to important diplomatic offices around the world. In the lead up to World War II, the Americans became increasingly interested in what the Japanese were communicating over Purple. US and British cryptographers had already broken some of its messages well before America's entry into the war. The intelligence they gleaned from Purple was code named Magic.
One of the most important pieces of Magic US cryptographers "found" was the 14-part Japanese diplomatic message ominously breaking off relations with the United States. That was at 1PM Washington time, December 7, 1941.
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