PEARL HARBOR: Magic Was the Word for It

U.S. citizens discovered last week that perhaps their most potent secret weapon of World War II was not radar, not the VT fuse, not the atom bomb—but a harmless little machine which cryptographers painstakingly constructed in a hidden room at Fort Washington.

With this machine, built after years of trial & error, of inference and deduction, cryptographers had duplicated the decoding devices used in Tokyo. Testimony before the Pearl Harbor Committee had already shown that the machine—known in Army code as “Magic”—was in use long before Dec. 7, 1941, had given ample warning of the Jap’s sneak attack—if only U.S. brass hats had been smart enough to realize it (TIME, Dec. 10). Now General Marshall continued the story of “Magic’s” magic. It had:

¶ Enabled a relatively small U.S. force to intercept a Jap invasion fleet, win a decisive victory in the Battle of the Coral Sea, thus saving Australia and New Zealand.

¶ Given the U.S. full advanceinformation on the size of the Jap forces advancing on Midway, enabled the Navy to concentrate ships which otherwise might have been 3,000 miles away, thus set up an ambush which proved to be the turning-point victory of the Pacific war.

¶ Directed U.S. submarines unerringly to the sea lanes where Japanese convoys would be passing.

¶ By decoding messages from Japan’s Ambassador Oshima in Berlin, often reporting interviews with Hitler, given our forces invaluable information on German war plans.

Uneasy Secret. So priceless a possession was Magic that the U.S. high command lived in constant fear that the Japs would discover the secret, change their code machinery, force U.S. cryptographers to start all over again.

General Marshall had a long series of bad moments after U.S. flyers, showing a suspicious amount of foresight, shot down Admiral Yamamoto’s plane at Bougainville in 1943. Gossip rustled through the Pacific and into Washington cocktail parties; General Marshall got to the point of asking the FBI to find an officer “who could be made an example of.” (The FBI, fearful of looking like a Gestapo, refused.) Once a decoder was caught in Boston trying to sell the secret. Once, well-meaning agents of the Office of Strategic Services ransacked the Japanese Embassy in Lisbon, whereupon the Japs adopted a new code for military attaches. This code remained unbroken more than a year later. The worst scare of all came during the 1944 presidential campaign, when George Marshall heard that Thomas E. Dewey knew the secret and might refer to it in speeches (see below).

Yet for all these fears, the Japs never discovered that the U.S. was decoding their messages. Even after the surrender, the Army still used Magic as a guide to occupation moves: though it had once been planned to send a whole army into Korea, Magic showed that a single regiment would be enough.