Magic (cryptography) - How Secret Was Magic?

How Secret Was Magic?

Public notice had actually been served that Japanese cryptography was dangerously inadequate by the Chicago Tribune, which published a series of stories just after Midway, starting on 7 June 1942, which claimed (correctly) that victory was due in large part to U.S. breaks into Japanese crypto systems (in this case, the JN-25 cypher, though which system(s) had been broken was not mentioned in the newspaper stories). The Tribune claimed the story was written by Stanley Johnston from his own knowledge (and Jane's), but Ronald Lewin points out that the story repeats the layout and errors of a signal from Admiral Nimitz which Johnston saw while on the transport Barnett. Nimitz was reprimanded by Admiral King for sending the dispatch to Task Force commanders on a channel available to nearly all ships.

However, neither the Japanese nor anyone who might have told them seem to have noticed either the Tribune coverage, or the stories based on the Tribune account published in other U.S. papers. Nor did they notice announcements made on the floor of the United States Congress to the same effect. There were no changes in Japanese cryptography connected with those newspaper accounts or Congressional disclosures.

Alvin Kernan was an aviation ordnanceman on board the aircraft carriers Enterprise and the Hornet during the war. During that time, he was awarded the Navy Cross. In his book, Crossing the Line, he states that when the carrier returned to Pearl Harbor to resupply before the Battle of Midway, the crew knew that the Japanese code had been broken and that U.S. naval forces were preparing to engage the Japanese fleet at Midway. He insists that he "...exactly remembers the occasion on which I was told, with full details about ships and dates..." despite the later insistence that the breaking of the code was kept secret.

U.S. Navy Commander I.J. Galantin, who retired as an Admiral, refers several times to Magic in his book about his Pacific theater war patrols as captain of the U.S. submarine Halibut. However, Galantin refers to Magic as "Ultra" which was actually the name given to the breaking of the German code. Upon receiving one message from Pacific Fleet command, directing him off normal station to intercept Japanese vessels due to a Magic message, Galantin writes. "I had written my night orders carefully. I made no reference to Ultra and stressed only the need to be very alert for targets in this fruitful area." Galantin had previously mentioned in his book that all submarine captains were aware of "Ultra" (Magic).

In addition, Army Chief of Staff George C. Marshall discovered early in the War that Magic documents were being widely read at the White House, and that "...at one time over 500 people were reading messages we had intercepted from the Japanese.... Everyone seemed to be reading them".