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 that cryptographers painstakingly constructed in a hidden room at Fort Washington.

With this machine, built after years of trial and 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 December 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, December 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 advance information 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.

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 attachés. This code remained unbroken more than a year later.^[43] 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 United States 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.

The letter, on stationery of the Chief of Staffs Office, bore a bold heading: TOP SECRET. FOR MR. DEWEY'S EYES ONLY. Candidate Thomas E. Dewey, his curiosity piqued, read rapidly through the first two paragraphs:

Tom Dewey looked up from the typewritten page. As he did, the word cryptograph, a few paragraphs below, flashed into his vision like a red traffic light. He made his decision quickly, folded the letter, handed it back. Colonel Carter W. Clarke (in mufti), who had flown from Washington to Tulsa to catch up with Tom Dewey's campaign, went back, his mission uncompleted.

It was September 1944. The campaign train rolled up through the Midwest, returned to Albany. A few days later, Tom Dewey received another visit from Colonel Clarke.^[44]

The Colonel, again in civilian clothes, handed over another letter from General Marshall. The General had changed his mind somewhat:

This time Tom Dewey read on. As he turned the pages, he became the first man outside the high command to know the full story of "Magic" and what it was accomplishing in the war against the Japs (see above). The letter closed with a plea:

Tom Dewey locked the letter in his files, went back to his electioneering. Though he had known before that the United States had cracked the Jap code, had suspected that this information cast grave doubts on Franklin Roosevelt's role before Pearl Harbor, he held his tongue. The War Department's most valuable secret was kept out of the campaign.

Recounting this story at the Pearl Harbor hearing last week, General Marshall recalled that he and Tom Dewey had never discussed the matter in person until they met at Franklin Roosevelt's funeral last April: "I asked Mr. Dewey to come with me to the War Department and I showed him current Magic showing Japanese movements. His attitude was friendly and gracious."

Had Marshall ever told Franklin Roosevelt of the letters to Dewey? Said Marshall: "The President died without knowing of it."

The Pearl Harbor Committee blithely tossed away one still-secret U.S. weapon. George Marshall's letters to Governor Dewey (see above) mentioned that the United States, with the help of the British, had decoded German as well as Japanese messages. George Marshall begged the Committee to cut out these references. The Committee refused.

Publication of the letters thus gave the Germans their first knowledge that their code had been broken. It was also a breach of diplomatic confidence with the British, who had let the United States in on the secret on the understanding that it would be kept.

Up to the witness stand stepped Lieut. General Leonard T. Gerow, chief of the Army's War Plans Division in 1941, to accept full blame for one of Pearl Harbor's most egregious errors. On November 27, a sharp warning of impending hostilities had gone out from General Marshall to Lieut. General Walter C. Short in Hawaii. On November 28, General Short replied that he had ordered an alert against sabotage – which was like saying he had a butterfly net ready for a tiger. Yet his reply was never challenged by Washington. Why?

Explained General Gerow: he thought the Short message was an answer to other communications. Said he: "If there is any responsibility in the War Department for failure. . . I accept that responsibility."

Then up stepped General Marshall himself to take part of the blame. He didn't recall seeing the Short message; he should have. "That was my opportunity to intervene and I didn't take it," he confessed. "Just why, I do not know."

The week's testimony also shed light on the warning that came too late – the message Walter Short received on December 7 at 2:58 p.m. Hawaii time informing him that the Japs were on the way.

On the night of December 6, Major General Sherman Miles, Chief of Intelligence, received from "Magic" decoders the first thirteen points of the strongly worded, final Jap diplomatic note being sent from Tokyo to its envoys in Washington. Next morning, some time between 7 and 8 o'clock, an assistant telephoned that he had "important" information. General Miles reached his office at 9 o'clock.

General Marshall had risen early, breakfasted at 8, looked over the Sunday papers, gone out for a horseback ride. (He usually rode for 50 minutes.) He was in the shower when an urgent message arrived by telephone from General Miles' assistant. He finished his bath, dressed quickly and went straight to the War Department. The time: 11:25 a.m.

A hastily gathered staff meeting decided that the Jap note meant war, that a warning should go immediately to Hawaii, the Philippines, the West Coast, the Canal. General Marshall called Admiral Harold R. ("Betty") Stark, then Chief of Naval Operations. "Betty" Stark thought by some obscure reasoning that further warnings would "only confuse" field commanders.

General Marshall wrote out a warning anyway, called Admiral Stark again to read it. Stark decided on second thought that the warning might as well go to Navy commanders as well. General Marshall sent it on to the Signal Corps that promised, according to General Miles, that it would be delivered in 20 minutes. It was then 11:50 a.m.; the attack was one hour and ten minutes away.

Instead of 20 minutes, the Signal Corps took eight hours and 28 minutes to get the message to Short (by commercial cable instead of Army radio). Nobody had bothered to check up on the Signal Corps; the General Staff took for granted that the message was going full speed ahead.

Why hadn't General Marshall used the telephone? His explanation: he knew that many phone calls – including transatlantic talks between Franklin Roosevelt and Winston Churchill – had been tapped; he feared that the Japs would intercept his call and label it an "overt act." Anyway, he said, even if he had phoned he would first have called the Philippines, where he thought the real danger lay.

Said George Marshall: "We thought Hawaii was the most improbable [target] of all. . . . I was inclined to feel the hazards were too great and they would not risk it."