MAGIC (communications intelligence)

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MAGIC was the overall code word for U.S. communications intelligence against the Empire of Japan, before and during World War Two in the Pacific. The code word itself was highly classified, and personnel knowing what it meant, much less what it revealed or how the breakthroughs were made, were under orders not to be captured alive. The latter usually meant staying out of battle areas, but, in such cases as that of Captain John Philip Cromwell, deliberately going down with a sinking submarine.

Japanese cryptosystems[edit]

While many Japanese subsystems were penetrated, the most important included:^[1]

• PURPLE machine: Mechanized diplomatic cipher
• JN25 (code): Naval superenciphered code

There were lower-level systems, some of which were more important than realized.

• PA-K2: A consular system, called Oite or O by the Japanese, but that was the only one not destroyed at the Honolulu consulate, and was being used to send final targeting information to the Pearl Harbor striking force
• TSU (called J by the U.S.): a moderately strong diplomatic cipher; manual and weaker than PURPLE
• LA: minimally secure system used for diplomatic administrative traffic

Program organization[edit]

There was no single point of control; responsibility was shared between the Signal Intelligence Service of the Army and Op-20 of the Navy. Much of the control was in Washington DC, although there were several field stations that did analysis as well as intercepting signals: Station CAST (Corregidor until its capture), Station HYPO (Pearl Harbor) and Central Bureau, Southwest Pacific Area in Australia.

Results[edit]

PURPLE was broken before the start of the war, and U.S. policymakers were reading the Japanese instructions to break diplomatic relations before the Japanese Embassy in Washington had read the complete message.

Breakthroughs into JN25, along with creative analysis of a "code within the code" to ensure the exact target, were credited with the "miracle at Midway." With specific knowledge that the Japanese intended to invade Midway Island, the Pacific Fleet was able to concentrate resources and decisively defeat the Japanese at the Battle of Midway. This battle, in which Japan lost four of its six large carriers, and highly skilled pilots, often is considered the turning point of World War Two in the Pacific.^[2]

MAGIC information revealed the planned inspection route of the Commander-in-Chief, Combined Fleet, Admiral Isoroku Yamamoto. After Presidential approval, a mission was mounted to intercept his aircraft and kill the most charismatic Japanese naval leader.^[3]

References[edit]