Magic was
the codename given for the American operation to break the Japanese
diplomatic and military codes. The Communication Special Unit (U.S.
Navy)
and the Signals Intelligence Section (US
Army)
worked together in monitoring the traffic of coded messages sent by
the Japanese Government and the Imperial Headquarters to their commanders
at sea and in the field.
In 1939
Japan began using a new cipher machine invented
by Jinsaburo Ito. Nicknamed the Purple Machine, the code was not broken
until September 1940 by the Army cryptanalyst William
Friedman. However, because of the large volume of intelligence
being received by the staff of Magic, they were unable to give adequate
warnings about the proposed attack at Pearl
Harbor.
With increases
in the number of people working at Magic they were able to discover
the attack plan at the Battle of Midway.
This enabled Admiral Chester
Nimitz to use this information to fight off a much larger
force and halt the Japanese offensive in the Pacific.
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