8

 

The U.S. Tackles Japan's Codes

 

 

When Secretary of State Stimson sniffed at the idea of reading other gentlemen's mail and closed down Herbert Yardley's Black Chamber, American cryptology seemed to have come to an end. It had not. Quietly, other agencies, from the FBI and the Federal Communications Commission to the army and navy, carried on the task, independently of each other and often involving rancorous internecine turf wars.

Inheriting Yardley's files, the U.S. Army Signal Corps in 1930 created the Signal Intelligence Service (SIS). To head it up, the corps hired William Friedman, whom many consider the greatest cryptologic genius of all time.

Friedman came to code work by a serendipitous route. Born in Russia in 1891, he was brought to the U.S. as an infant. His family settled in Pittsburgh, and as a high school youth, he became caught up in a Jewish "back to the land" movement which led him, when he was a graduate student at Cornell University, to plan a career in plant genetics. In 1915 an eccentric millionaire cotton merchant named George Fabyan went to Cornell in search of a geneticist to work at his Riverbank Laboratory, near Chicago, on improving crop strains. Friedman, recommended by one of his professors, became head of Riverbank's Department of Genetics and involved himself in such Fabyan projects as planting oats by the light of the moon to see whether the phases made any difference in their growth.

Fabyan, who had the wealth to support his flights of fancy, also became intrigued by a woman whose research had convinced her that Francis Bacon had written the works attributed to William Shakespeare and, what was more, had included coded messages to that effect in the early folios of the plays and poems. She claimed the secret messages also revealed that he was the illegitimate son of Queen Elizabeth I and the rightful heir to the British throne. To fill out his team conducting this research, Fabyan hired Elizebeth Smith, a Hillsdale College graduate, whose mother had insisted on the unusual spelling of her name to prevent its being shortened to Eliza.

The theory of the Bacon codes was based on variations in the typefaces in the folios. Handy with a camera, Friedman helped the project by making photo enlargements of the type fonts. He was drawn to the cryptographic work. "Something in me," he commented later, "found an outlet."

Since Europe was then at war and American military involvement was becoming increasingly likely, Elizebeth and William foresaw the need for the U.S. to become more proficient in secret communications. Ever the opportunist, Fabyan enthusiastically supported this new phase of their research. For a time Riverbank was the only organization in the country skilled in deciphering coded messages. Their mutual professional and personal interests led Elizebeth and William to marriage in 1917.

When, later that year, the army created its Cipher Bureau, Fabyan arranged for the Friedmans to conduct classes in cryptography for army officers. A famous photo from that era shows Elizebeth and William surrounded by their eighty bright young students in khaki. The students' faces are turned either directly toward the camera or away from it to register a bilateral coded message: Bacon's aphorism "Knowledge is power."

As texts for his classes, Friedman began writing a series of booklets on cryptography—one of them with Elizebeth as collaborator. Impressed, the army brass offered him a first lieutenant's commission. He spent the last five months of World War I on General Pershing's staff in France, concentrating on breaking German codes. The experience gave him ideas that subsequently he was to use with great effect. On his return to Riverbank he published a new booklet, The Index of Coincidence and Its Application to Cryptography. David Kahn has written that it "must be regarded as the most important single publication in cryptology. It took the science into a new world."

Cryptanalysis had, previously, been rather an occult process in which the would-be breaker pored over a ciphertext waiting for some intuitive insight to lead to a solution. Friedman's "new world" consisted of methodically applying a statistical and mathematical science to codebreaking. His new booklet added a useful technique. He had observed that if the horizontal lines of a message are arranged so that the letters are placed in vertical rows precisely below each other, now and then the same letter will appear, the one directly beneath the other. This coincidence, he had determined, will vary in frequency with each language. In English it occurs in 6.67 columns of every 100. This was a step forward in cryptanalysis that gave Friedman a tool in analyzing the new machine-encoded ciphers when they began to appear.

During the 1920s both Friedmans were engaged in code work for the government. William made national headlines when he cracked the codes of the conspirators in the Teapot Dome scandal and helped send several of them to prison. He also became chief codebreaker for the War Department, where he developed the reputation of being like Midas, except that everything he touched turned not into gold but into plaintext. Elizebeth, in addition to starting a family, helped the Department of Justice and later the Treasury Department in efforts to enforce Prohibition. She broke the increasingly sophisticated codes of the rum-running syndicate and testified against them in well-publicized court cases.

When, in the autumn of 1929, William became chief of the newly created Signal Intelligence Service, he was empowered to begin building a cryptographic staff. He requested mathematicians, and chance gave him Frank Rowlett, a high school mathematics teacher from Virginia, and two graduate mathematicians from the City College of New York, Solomon Kullback and Abraham Sinkov. Also foreseeing the need for a translator fluent in Japanese, Friedman was swayed by a congressman to hire his nephew, John Hurt.

There were only five of them, but what a team they turned out to be! Friedman adroitly challenged his staff, first by having them study his cryptography writings, then by giving them relatively easy ciphers before moving on to more difficult examples. He threw at them a Great War German cipher that he, with a French cryptanalyst, had had considerable trouble in cracking. The team surprised him by the speed with which they broke it. He turned them loose on the Hebem mechanical enciphering device, which had taken him six weeks of intense concentration to solve; they broke it in less than a month. They were ready, Friedman decided, to take on "real work": breaking the Japanese nonmachine "pencil and paper" codes then current. To Hurt's delight the cryptographers were soon giving him plaintext to translate and interpret. Sinkov recalled of Friedman, "His teaching was such that we developed on our own."

The second heavy responsibility placed on the Friedman five has already been mentioned: the work of developing secure cryptographic systems for the U.S. that resulted in the Sigaba M-134. Because of security restrictions, Friedman couldn't reveal even to his own lawyers the nature of the patents he was seeking. He had to write his own briefs.

 

 

Conquest of the Red Machine

 

As the 1930s unfolded, Friedman and his SIS team faced the challenge of breaking into the code machines the Japanese Foreign Office had introduced. First to be tackled was the Type A machine, the Alphabetical Typewriter 91.

Rowlett, in his memoir, The Story of Magic, gave a progressive account of how the Friedman team analyzed the Japanese machine and slowly solved it. They began by observing a quirk in the system. In their new machine ciphers the Japanese used the Roman alphabet to spell out phonetic equivalents of Japanese words, and in this new machine cipher, six letters occurred with high frequency, while the other twenty appeared less frequently. Friedman and his young analysts determined that the six consisted of the five vowels plus the letter V. The SIS was able to exploit this discovery by looking for patterns. One such pattern was that in the Japanese phonetics the Y was always followed by one of the other vowels and often by a doubling of them—YUU or YOO—and it was often preceded by R or K—RYUU, RYOO, KYUU, KYOO. Another pattern was the combination of the letters that, when deciphered, produced oyobi, the Japanese word for the English "and." In their analysis the Friedman crew noticed that their descriptions of these identifiable combinations held for only forty-two positions; then the machine introduced a stepping pattern, moving the whole process forward to a new equivalent of the letters. From those beginnings they were able gradually to open up the entire encoding system and produce plaintext from the messages.

Type A, they decided, was a rotor machine, a Japanese variation on the principles of the Enigma. Its encipherment mechanism included two rotors, each of which had twenty-six electrical contacts wired around the circumference of one of its sides. There was also a gear wheel with forty-seven pins projecting from it. A unique feature was that the gear wheel pins were removable. If a pin was in place, it moved the rotors forward with one stroke of the typewriter keys. If it was removed, the machine jumped over that contact, giving the machine an irregular movement meant to foil cryptanalysts.

The machine simply didn't have enough complexity to withstand the SIS team's attack. They were able gradually to open up the entire encoding system and produce plaintext from Type A's messages.

While solving its riddles, the cryptanalysts referred to it often as "the Japanese code machine." They realized that this term was so descriptive that its use might result in an inadvertent security break. They gathered together to settle on a cover name, and eventually the discussion got around to considering colors. "All of us were in agreement," Rowlett wrote, "that the first color of the spectrum was an excellent choice as a cover name for the first cipher machine that we had solved which was actually used for enciphering official messages of a foreign power. And from this moment on, the Japanese diplomatic cipher machine was always referred to as the 'Red Machine.'"

In short order the five team members began to flood the president, the secretary of state and the chiefs of the army and navy with John Hurt's translations of Japanese diplomatic exchanges. Friedman, incidentally, had overcome the usual interservice animosities and developed a friendly, mutually beneficial collaboration with Commander Laurance F. Safford, his counterpart in charge of the navy cryptologists.

Appreciation of the team's exploits took the practical form of increased funding for IBM processing machines, a move to more spacious quarters and an increased staff, including the hiring of bright young women such as Genevieve Grotjan.

 

 

The Breaking of Purple

 

In late 1938 and early 1939, Friedman and his expanded team began deciphering Red messages announcing the distribution of Red's replacement, angoo-ki taipu B, or "cipher machine Type B." They hoped that the new machine would be only a modification of Red, but a new series of messages sent in by U.S. intercept stations beginning on March 20, 1939, dashed that hope. They proved unbreakable by the methods applied to Red cryptanalysis.

As the Americans were to learn, slowly and painfully, Japanese cryptographers had built on their experience with Red and had perfected a machine whose principles were completely different from those in the German Enigma or other code machines and presented complexities greater than those of the Enigma.

Again Friedman met with his team to choose a new cover name. Sticking to the light spectrum, they chose the color Purple.

Ronald Clark, in his biography of Friedman, The Man Who Broke Purple, told of the felicitous decision made early in 1939 by General Joseph O. Mauborgne, chief of the Signal Corps. Disturbed by the slow progress being made in solving the Purple machine, Mauborgne saw that Friedman was too burdened by administrative details and work on the Sigaba to be effective in the attack. In February 1939, consequently, he ordered Friedman to drop all other duties and concentrate on Purple cryptanalysis. "Friedman," wrote Clark, "now began the most acute eighteen months of intellectual effort he was ever to undertake."

Rowlett's memoir suggested that Friedman had much less to do with the cracking of Purple than did Rowlett and other members of the SIS. However it was, progress did come at a brisker pace. Japanese errors helped. Reliance on ceremonial diplomatic forms of address such as "I have the honor to inform your excellency" handed the analysts cribs of probable plaintext to test against the ciphertext. Purple messages sent to embassies equipped only with the Red machine were obligingly repeated in that code, offering another angle from which to unravel the cipher. And on occasion a sender would admit having erred in one of his settings and re-send the message correctly, supplying the analysts with an insight into the proper setting.

Exacting analysis also showed that Purple offered the same structural opening as Red. Its system included a subsequence of six often-used letters enciphered separately from the other twenty. Unlike in the Red, though, these six could include any letter rather than just the vowels plus V. Rowlett drew up plans for a machine that would be an equivalent of the mechanism the Japanese used for enciphering and deciphering the sixes. Friedman, impressed with the plan, recommended that SIS employ Captain Leo Rosen, who had joined the Reserve Officer Training Corps at MIT while studying to become an electrical engineer.

The hiring of Rosen turned out to be another fortunate choice. Very quickly after being briefed on the nature of the Purple machine and of Rowlett's plan for cracking the sixes, he saw what was needed. This was nothing more than the use of standard telephone switchboard stepping switches. The switches were acquired, the "Six Buster" machine was built, and it did its job perfectly.

One of Safford's cooperating navy analysts, young Harry L. Clark, has been credited with raising the question of whether the Japanese, in their new machine, might be using an entirely different enciphering mechanism than those of other code machines. Could it be that the machine was based on the same stepping switches Rosen had applied in the Six Buster? Rowlett, Rosen and the others thought so, but before that question could be answered they had to gain a great deal more knowledge about the groups of twenty letters. Being able to tell where the sixes' letters occurred in a message helped by pinning down likely cribs. What was needed was a much broader base of plaintext equivalents of the twenties. The team made up large worksheets on which they recorded from each day's intercepts the most probable pairings of plaintext and ciphertext equivalents.

The process took most of a painstaking year. Then Genevieve "Gene" Grotjan, who had been doing the monotonous task of compiling indicator worksheets, made the breakthrough. Rowlett has described being in his office conferring with colleagues Bob Ferner and Albert Small when Grotjan broke in, visibly excited. She wanted to show them something in her worksheets. Leading them to her desk, she indicated where she had drawn circles around selected plaintext and ciphertext equivalents. Further, she had circled the same relationships on other worksheets. What she had found were consistent relationships, proofs that the coded letters were invariably linked with the plaintexts. As Rowlett characterized her discovery, it was "the first case of positive evidence that we were on the proper course to a full recovery of the Purple machine."

After she had pointed to the last example, Rowlett recalled, "she stepped back from her desk, with her eyes beaming through her rimless glasses, obviously thrilled by her discovery." The others immediately realized the importance of what she had found. "It was a beautiful example," Rowlett wrote, "of what we had hoped our search would uncover."

He described what followed: "Small promptly started dancing around her desk, raising his arms like a victorious prizefighter, and yelled 'Whoopee.' Ferner, who was usually very quiet and not very much inclined to show enthusiasm, clapped his hands, shouting 'Hurrah! Hurrah!' I could not resist jumping up and down and waving my arms above my head and exclaiming 'That's it! That's it! Gene has found what we've been looking for!'"

They made so much noise that Friedman came out of his office and asked, "What's this all about?"

Rowlett led Friedman to Grotjan's desk and tried to let her tell the story of her discovery. But she was so overwhelmed, and by now weeping in her excitement, that he had to take over.

Friedman carefully examined each of the areas and grasped their implications. He saw that with this break his team could go forward with actually building a replica of the Purple machine. "Suddenly he looked tired and placed his hands on the edge of the desk and leaned forward, resting his weight on them," Rowlett recalled. "I pulled a chair forward and offered it to him. Seated, he addressed everyone in the room: 'The recovery of this machine will go down as a milestone in cryptanalytic history. Without a doubt we are now experiencing one of the greatest moments of the Signal Intelligence Service.'"

The team forged ahead toward producing a clone of the Purple machine. Further work along the lines of Grotjan's discovery confirmed what Rosen and his colleagues had suspected: the devices that caused Purple to advance at regular intervals from one encipherment stage to another were stepping switches, both for the sixes' subsequence and for the twenties'. "Rosen," Rowlett wrote, "promptly started to prepare the layout of a complete cipher machine to duplicate the cryptographic functions of the Purple machine."

Postwar comparisons with the real Purple machine verified that Rosen's replica reproduced the original's complex wiring, its use of stepping switches, its intricate plugboard. If ever there was a feat of visionary engineering, this was it: to imagine the inner workings of an intricate secret machine and produce a copy that was so close an approximation of the original that of the several hundred connections in the clone, only two were wired differently from the Japanese machine. As various commentators have noted, the achievement surpassed those of the Poles and the British, who had commercially available models to serve as guides.

On September 25, 1940, just two days after Germany, Italy and Japan had signed the Tripartite Pact pledging all three to mutual support, Rowlett sat at the keyboard of the new machine in Washington's Munitions Building and started typing the ciphertext of a message. "The machine performed beautifully," he wrote in his memoir, "producing a letter-perfect plaintext."

Once again the SIS had opened a secret window through which the U.S. could spy on Japan's diplomats. As we shall see, however, the eventual consequences of the conquest of Purple were to go far beyond listening in to diplomatic chitchat.

Documentary sources make it clear that William Friedman was not the man who broke Purple. He himself said, "Naturally this was a collaborative, cooperative effort on the part of all the people concerned. No one person is responsible for the solution, nor is there any single person to whom the major share of the credit should go."

Nevertheless, the strain of those eighteen months took their toll on him. In December 1940 he collapsed and was rushed to the neuropsychiatric ward of the army's Walter Reed Hospital. He remained there until March 1941 and returned to full-time duty only on April 1. By then additional Purple replicas had been built and distributed to Allied nerve centers. The flow of information meant that both Britain and the U.S. could navigate the twists and turns of Japanese diplomacy.

General Mauborgne thought of Friedman's team as "the magicians" and gave the whole U.S. codebreaking operation the cover name of Magic. Later in the war the English code name Ultra began also to be applied to the U.S. program. In these pages, to avoid confusion, Ultra has been applied to decrypts of the Enigma and Magic to the success over Purple.

 

 

Tracking the Imperial Navy

 

During the 1930s the U.S. Navy employed the largest cryptologic branch among the U.S. military services. This made sense in view of the navy's responsibility to provide the first line of defense against the mounting threat of Japanese naval power. Navy leaders needed to organize the strongest effort possible to decode the signals of the Imperial Navy. But these were times when isolationist America wanted to avoid a repeat of the Great War and also when the American economy was in the grip of the Great Depression. The consequent lack of funding starved U.S. military services almost to impotency.

With its share of the inadequate defense budget the navy nevertheless built and operated a circle of radio intercept stations around the Pacific Rim and conducted a three-phase cryptologic program. One was direction finding—the use of triangulation to locate specific Japanese transmitters. The second was traffic analysis—determining from merely the sending of messages and the call signs of the senders the movements of the Japanese fleet. The third was cryptanalysis—the attempt to penetrate the content of the messages themselves. The headquarters of the cryptanalytic program was based in Washington, with outposts at Pearl Harbor and at Cavite on the island of Luzon in the Philippines.

The navy took another foresighted step. It assigned bright young officers to three-year stints in Japan, expecting them to use this duty to become familiar with the Japanese people and to develop fluency in the Japanese language.

For all the navy's prescience, however, it placed serious obstacles in the way of any career officer interested in cryptology. One was the low esteem, even contempt, in which intelligence work was generally held; time spent at it was viewed as a detour, not a step forward. Another was the encrusted rule that an officer could put in only a certain time of desk work before going on sea duty. All through the 1930s, the main source of continuity in navy cryptanalysis work was supplied by a civilian, "Miss Aggie"—Agnes Meyer Driscoll, who stayed put in Washington, did whatever codebreaking she could and trained the young officers as they came and went.

So it took a strong element of determination and grit for the navy officer to persist in pursuing code work. Fortunately for the U.S., men such as Edwin Layton, Thomas Dyer and Wesley "Ham" Wright possessed that determination and grit. So did Joseph John Rochefort.

Rochefort began his navy duties as an enlisted man and rose, by sheer ability, to head the navy's cryptographic section from 1925 to 1927. Ordinarily the navy was sending only bachelors on the three-year Japanese-learning assignment. It made an exception in Rochefort's case: in 1929, despite his being a married man with a child, he went to Japan for three years as a language student. After another half year in naval intelligence he spent the next eight years on sea duty.

In June 1941, Rochefort returned to cryptology. He was given command of the radio intelligence unit in Hawaii, to which he applied the cover name of the Combat Intelligence Unit. Within the service it became more familiarly known as Station "Hypo"—the standard name for H in the International Signal Code. While Rochefort's command included one hundred officers and enlisted men, the great majority were assigned to direction finding and traffic analysis. Only a small number were left over to concentrate on cryptanalysis.

A contest of wills was already forming between the cryptologic staff of the Washington naval headquarters and the staffs of the two outposts, the one known as Cast, from the C of Cavite, and Rochefort's Hypo on Oahu. The Washington operation, known as Op-20-G, wanted to maintain overall control. Its chiefs decided which Japanese codes the other two stations would be assigned to work on and which ones it would hold to itself.

Japan's navy relied not on cipher machines but on codes in the old sense: the use of codebooks in which a vocabulary of thousands of information elements such as harbor or battleship were given letter or numerical equivalents—98765, say, or 12345. The Japanese went beyond merely using the codebooks. When a message was encoded in its four- or five-number equivalents, it was subjected to a superencipherment, a further scrambling of the code numbers. The cryptanalyst faced the formidable task of stripping away this first barrier before getting at the code groups themselves.

The Japanese used a diversity of codes with varying degrees of cryptographic security. The two toughest were the "flag officers' system" and the main naval standby, which the U.S. Navy cryptologists identified as JN-25 because it was the twenty-fifth of the naval codes they had worked on. Lesser codes dealt with administrative matters, personnel changes, weather forecasts and the like.

In an unfortunate turn, as subsequent events proved, Rochefort's Hypo unit was assigned work on the flag officers' system, while only OP-20-G and Cast were responsible for trying to solve the JN-25 code. Washington also monopolized work on a lesser code, J-19, even though this was the code used by the Japanese consul in Honolulu. In another strange twist, the Cast operation in the Philippines had a Purple machine, and three were sent to the British, but the one for Hawaii was not scheduled to arrive until late December 1941.

Rear Admiral Edwin T. Layton, head of intelligence for the Hawaiian commander Admiral Husband E. Kimmel, told in his revealing memoir, And I Was There, how Kimmel was, in July 1941, cut out of the loop of those receiving Magic information, ostensibly for security reasons, and how his own pleas to receive Magic decrypts were rebuffed.

These quixotic assignments of responsibilities helped precipitate the coming disaster.

Rochefort and his command's efforts were wasted on the flag officers' code. Neither they nor any other Allied group ever succeeded in breaking it—partly because it was used so sparingly they never had a sufficient number of intercepts to work with. One of the most troubling what-ifs of the war was subsequently raised by Layton, Rochefort's superior: what if Rochefort, whom Layton considered the navy's most gifted performer in both linguistic and cryptanalytic terms, had been concentrating on JN-25, with which neither OP-20-G nor Cast was making serious headway? Lay-ton's answer was that if the mass of JN-25 intercepts that awaited decoding in Washington had been given to Rochefort to penetrate, the catastrophe at Pearl Harbor could have been averted. The same was true of the J-19 code. When it was eventually tackled, after the fact, its messages were found to, include highly specific exchanges between Tokyo and the Oahu consulate about U.S. warships docked at Pearl Harbor.

Even though Rochefort's team had to derive most of their intelligence from direction finding and traffic analysis, they went at their work in a manner that differed sharply from the general practices then in force on Oahu. Even in 1941, with war an increasing menace, slack peacetime ways were the rule. In many units the men were on duty only one day out of four; a commander who tried to impose a change to one day out of three met with almost an insurrection, especially on the part of the servicemen's wives. Rochefort, by contrast, aware of the Imperial Navy's ever more belligerent actions, drove himself and his men hard. As W.J. Holmes has written in Double-Edged Secrets, his record of those times, "Had I not witnessed it, I never would have believed that any group of men was capable of such sustained mental effort under such constant pressure for such a length of time."

With estimates based on the limited means of Sigint available to Hypo, Layton and Rochefort did their best to keep Admiral Kimmel informed about the Japanese military's plans. They could tell him with confidence that the Imperial Navy had organized a powerful force in Taiwan and Indochina. And where might this force strike? The intelligence officers' best guess was that it was poised to conquer Southeast Asia and the Netherlands East Indies.

Their estimate made sense. The English, Dutch and Americans had imposed an oil embargo on Japan. The Imperial war machine faced declining energy reserves. Japan's most likely response, the officers told Kimmel, was to seize the oil fields of the East Indies.

Layton and Rochefort were also intensely aware that the Japanese were moving southward, island jumping in their progress toward Australia. They had moved into the Marshall Islands southwest of Hawaii. The intelligence officers saw the Marshalls as the most likely base for an attack on Oahu. On their say-so, Kimmel used his inadequate air fleet to patrol more to the south and west than to the north.

The guesses by Washington ranged all over the Pacific map. The navy's chief war planner dogmatically asserted the attack would fall on the Soviet Union's easternmost provinces. Others speculated the coast of California, the Panama Canal or the Aleutian Islands, off Alaska. In a memorandum submitted to President Roosevelt ten days before the attack, Admiral Stark warned that it might fall on sites as remote as Thailand, Malaya or the Burma Road, but made no mention of Pearl Harbor. The strongest response by Washington's top brass, however, was the decision to strengthen the air fleet under the command of General Douglas MacArthur in the Philippines. A large flight of B-17 bombers was sent from the West Coast to the Philippines, with stopovers on Midway and Wake Islands. As an indication of how little anyone in power expected an attack oh Pearl Harbor, Kimmel was ordered to load half his fighter planes onto the two aircraft carriers available to him—the third was in the U.S. for an equipment refit—and deliver them to Midway and Wake. There the fighters would await the B-17s and escort them on their way to the Philippines. A smaller squadron of bombers was also to fly to Oahu.

For Layton and Rochefort, the most worrisome aspect of their reporting to Kimmel was that they could not determine with any certainty the whereabouts of Japan's aircraft carrier force. They could not know it, but they were being tricked. Fake radio traffic made the men both at Cast and Hypo believe that the carriers were in home waters. In fact, the carriers had been ordered to observe radio silence, so there was no direction finding or traffic analysis call signs to give their location away. Instead of idling close to home, the carriers, in the midst of their huge escorting fleet, were sneaking down toward Hawaii.

 

 

The Debacle at Pearl Harbor

 

The question still rankles those who lived through the experience: how, with Purple solved and three different signals intelligence units concentrating on Japanese naval codes, did the U.S. fail to anticipate Commander Isoroku Yamamoto's Hawaiian surprise that put out of action a large part of the U.S. Pacific Fleet and cost 2,403 American lives?

William Friedman himself gave the most succinct answer: "There were no messages which can be said to have disclosed exactly where and when the attack would be made"—at least not among the messages that were decrypted.

In retrospect, of course, investigators probing into the disaster found reams of evidence that should have awakened U.S. commands to the possibility of the assault. But the definitive proof that was necessary to pierce through lax peacetime attitudes and clouds of uncertainty never came.

Books and long Internet articles have been written supposedly "documenting" that American inaction was the deliberate result of a Franklin Roosevelt "conspiracy" to plunge the U.S. into war on the side of his friend Winston Churchill. These writers have characterized FDR as a "Communist" and a "traitor" who knew the Japanese plans but purposely avoided taking action because he wanted them to come to fruition.

Historian John Keegan has said these charges "defy logic." They fail to mention that to have achieved so malign a purpose, Roosevelt would have had to persuade the army chief of staff George Marshall and navy chief Harold Stark to go along with him. Professor Gordon W. Prange, who spent thirty-seven years researching At Dawn We Slept, dismissed the conspiracy charges as "an absurdity." Ronald Lewin labeled them "moonshine." In her respected work Pearl Harbor: Warning and Decision, Roberta Wohlstetter wrote that hostile critics of FDR "confuse his frank recognition of the desirability of an incident with knowledge of the Pearl Harbor attack." In his 2001 book, Roosevelt's Secret War, Joseph E. Persico reported on his research showing that on the night before Pearl Harbor, FDR actually drafted an appeal to Emperor Hirohito "to join him in a statesman-to-statesman effort to stave off disaster"—hardly the act of a leader hoping to see that disaster happen.

The sacrifice of ships and sailors at Pearl Harbor is most honestly seen as the necessary price paid for shaking off the complacency that beset the public and military alike. The Japanese timed their attack to fall on a Sunday morning because they knew full well that the American navy wanted, like everyone else, to enjoy its weekend. More ships would lie in port then than at any other time of the week, and the guard systems would be least manned.

Even so, the codebreakers came agonizingly close to ringing the alarm bells. All during 1941 the Purple decrypts kept U.S. leaders informed on the instructions Tokyo's Foreign Office was sending its embassy in Washington. To read these messages is to glimpse a group of Japanese diplomats caught between the harsh demands of the military and the unwillingness of the Americans to accede to the terms the embassy was empowered to offer. Purple told of Japan's foreign minister desperately seeking some concession from the U.S., knowing the alternative was that "a lamentable situation will occur." This sense of urgency was heightened after October 16, when the moderate government of Prince Konoe fell and was replaced by the jingoistic Tojo cabinet. On November 26 the U.S. State Department presented its conditions for resolving the negotiations. Knowing these would be unacceptable to Tojo, Tokyo's diplomats pleaded with their embassy staff to secure some crumb of a compromise; otherwise "the fate of the Empire hangs by the thread of a few days" and "things are automatically going to happen." Finally, on December 6, Tokyo warned the Washington staffers to expect a long reply to the American proposal. It came in fourteen parts, the last of which was intercepted at three a.m. on December 7. Merely rehashing the Tojo cabinet's intransigence, it ends with the ominous words that "it was impossible to reach an agreement through further negotiations." A four thirty a.m. intercept instructed the ambassador to "submit to the United States government (if possible the Secretary of State) our reply to the United States at 1:00 p.m. on the seventh, your time." And at five a.m. the final message came through, ordering the embassy to destroy its code materials.

The Americans in Washington who saw these decrypts understood their meaning. Roosevelt himself said, "This means war." But from that point on, an incredible series of mistakes blocked effective response to the warnings.

FDR, failing to notice that the one p.m. deadline was just past dawn at Pearl Harbor, followed the general line of thinking that the attack would come on Southeast Asia. So, while he could have called Hawaii on his scrambler phone, he did not, because Pearl Harbor seemed an unlikely target for the Japanese.

Admiral Harold Stark, chief of Naval Operations, could have called Kimmel, but not realizing that the Hawaiian commander was no longer receiving Purple decrypts, he presumed Kimmel was as fully informed about the crisis as he was.

General Marshall could have used his scrambler phone to call General Walter Short, his commander in Hawaii. Not trusting the phone's security, however, he asked that his warning message be sent by radio. It happened that radio interference that morning was bad; Marshall's message went by commercial telegraph to San Francisco and from there was relayed seven, hours later. A messenger on a motorcycle delivered it to General Short only after the Japanese planes had completed their first run.

In Hawaii, as well, the alarm was nullified by slipups and errors of judgment. Two privates manning a radar station on Oahu detected the oncoming Japanese planes and phoned in their report. But the lieutenant on duty knew that the flight of B-17s from the mainland was due to arrive that morning, presumed that these were causing the blips on the privates' screen and told them to forget it. The navy had both air and ship patrols operating. Both reported seeing unescorted submarines and launched attacks against what were later revealed to be Japanese midget subs trying to augment the mayhem at Pearl Harbor. The officer in the Naval Operations office, hearing these reports, knew immediately that "we were in it." Before he could rouse an official response, though, the Zeros were already incoming.

One possible warning in which the cryptanalysts of OP-20-G in Washington placed great store came to be known as the "winds execute" message. The Japanese had signaled to their outposts that in the case of an emergency, such as cutting off diplomatic relations, they would add to regular radio weather forecasts a "hidden phrase code" calling for the destruction of code machines and materials. The code for the termination of relations with the U.S. was "east wind rain," that for the USSR "north wind cloudy," and that for Britain "west wind clear." Ralph T. Briggs, then a twenty-seven-year-old U.S. Navy communications intelligence technician in Washington, has sworn that he did receive the fateful words "higashi no kase ante"—"east wind rain"—embedded in a Tokyo weather broadcast on the morning of December 4. Briggs recalled recognizing the message's importance and reported that with his "heart pounding and adrenaline flowing," he informed his superiors and received the congratulations "Well done" from Captain Laurance Safford, founder of the navy's Communications Intelligence operation. Together, Briggs and Safford thought they had produced the bit of vital information that would alert the navy to the coming attack.

From that point on, however, the story of Briggs's intercept becomes clouded in mists of confusion and, it would appear, deliberate cover-up. Higher officials in the chain of command failed to act on the message and later denied receiving it. Briggs's report on the message disappeared from the files.

In planning the Pearl Harbor raid, Admiral Yamamoto saw it as the way out of a personal dilemma. A blunt bullet of a man who had been a language student at Harvard and had served as a naval attache in Washington, he understood America and the Americans better than his colleagues and had argued in prewar councils that to provoke war with the U.S. was folly. "The United States would never stop fighting," he was quoted as saying, "and ultimately we would not be able to escape defeat." Yet he also came to realize that the momentum toward war could not be stopped. He persuaded himself that by destroying the U.S. fleet in Hawaiian waters, he could strengthen the isolationist spirit in the U.S. and weaken the will to fight, generating a desire for a negotiated peace. As Admiral Samuel Eliot Morison wrote in his multivolume History of United States Naval Operations in World War II, Yamamoto "knew that he must annihilate the United States Fleet in 1942 or lose the war."

The attack on Pearl Harbor, carried out by a task force under the command of Vice Admiral Chuichi Nagumo, achieved nearly everything Yamamoto had hoped for. His planes sank or seriously damaged eighteen U.S. naval vessels, including eight battleships at anchor. Because General Walter Short, the army commander, had interpreted the warnings from Washington as orders to guard against sabotage from within the islands rather than attacks from without, he had grouped his aircraft in tight circles to make them easier to guard, allowing Yamamoto's raiders to destroy them en masse. And the Japanese admiral could take satisfaction in knowing his planes had put out of action broad ranks of servicemen who died or were seriously wounded.

Yamamoto had secured nearly everything he sought. He remained discontent, however, for two reasons. He had been led to believe the leaders in Tokyo would declare war before his planes struck. That was the plan, but it was thwarted by a series of blunders and delays. The admiral felt his honor had been sullied, and he knew the effect on Americans would be the opposite of desiring to negotiate a peace settlement. His second disappointment was that the U.S carriers were absent—they were on their plane-delivering mission to Midway and Wake.

The Japanese celebrated Pearl Harbor as a great victory. As for the U.S., the wound to the American psyche seemingly could be healed only by the cashiering of Kimmel and Short, the injustice of which is richly documented in Layton's memoir, and by the interminable investigative commissions and embittered congressional hearings that filled thirty-nine volumes of discordant testimony.

Yet in the long sweep of history it was a huge miscalculation by the Japanese. Admiral Morison's history summed up the attack as a "strategic imbecility." To have an enemy plot a vicious sneak attack even as its diplomats were carrying out a pretense of polite negotiations united the American people as nothing else could have. Pearl Harbor cleaned the decks of questionable commanders and brought in bright, energetic new leaders. It accelerated the American productive machine in turning out the masses of materiel that in the end would overwhelm the enemy's resources. It dashed the Japanese hope that they could achieve in the 1940s what they had accomplished in the 1905 settlement with the Russians: an advantageous peace without any attempt at invading enemy territory. As for its real effect on American naval power, the Japanese, as a U.S. admiral told Gordon Prange, "only destroyed a lot of old hardware." In fact, the raid failed to accomplish even that. The shallow waters of the anchorage permitted the salvage and repair of most of the crippled vessels; only two battleships—Arizona and Oklahoma—were beyond recovery. And the obvious surprise of the attack confirmed the Japanese in the belief that their codes were inviolable.

An odd corollary to the Pearl Harbor raid came in the Philippines, where Douglas MacArthur was the commander in charge. The Japanese planned their raid on the American bases on Luzon to follow as soon after Pearl Harbor as they could manage. But there was a two-hour time zone difference. In addition, fog delayed the departure of the mission. Consequently, MacArthur and his aides had nine hours to prepare for the Japanese assault. Yet they were strangely dormant, not even dispersing the aircraft lined up on their airfields. Dwight Eisenhower subsequently told an interviewer that MacArthur, his former commander, had some notion that the Japanese would not attack the Philippines. But attack they did, and their surprise was complete. "We still could not believe," a Japanese flier later recalled, "that the Americans did not have fighters in the air waiting for us." The U.S. lost more than one hundred planes—a good portion of the Philippines force—and suffered more than two hundred casualties. Admiral Layton has tartly pointed out that for this dereliction, in contrast to the treatment of Kimmel and Short, MacArthur was not even censured.

Though a smashing victory, Pearl Harbor's effects were so temporary that Yamamoto felt compelled to begin quickly the planning of another surprise strike—one whose outcome would be entirely opposite to his success at Pearl. Japanese Admiral Tadaichi Hara perhaps summed it up best in his postwar analysis: "We won a great tactical victory at Pearl Harbor and thereby lost the war."

They lost it in good part because of the harsh light the Pearl Harbor raid cast on the inadequacies of the U.S. intelligence system. The lack of a Purple machine in Hawaii has already been noted. Also highlighted were the system's ridiculously slow methods of gathering information. Sigint results from Oahu and Cavite were often dispatched to Washington in weekly bundles aboard a Pan American clipper; if the flight was canceled, they went by surface ships. The list of high-level recipients was also seen as far too restrictive: commanders with the strongest of all needs to know were not included. In Washington the methods for disseminating the information were cumbersome in the extreme. Copies of that vital fourteenth part of the final Japanese series to its embassy, for example, were locked into dispatch boxes and hand-carried by two officer-couriers making the rounds of the White House, the State Department and the offices of the military chiefs.

Japan's Pearl Harbor raid had two powerful effects on Station Hypo and Joe Rochefort. First, it left him with a profound sense of guilt that he had been unable to warn his admiral of the coming attack. Despite the fact that he had not been assigned the code from which he, with his deep knowledge of the Japanese mind and the Japanese language, might well have extracted the information, he felt that he had let his boss down. As he said in his oral reminiscence recorded in 1969, "An intelligence officer has one task, one job, one mission. That is to tell his commander, his superior, today, what the Japanese are going to do tomorrow. . . . We did not inform Admiral Kimmel prior to December 7th that the Japanese were going to make the attack. . . . Therefore we failed." His wounded conscience drove him and his closest associates to work twenty-hour days to make sure nothing like it happened again.

The second result was that just days after the raid, Washington had second thoughts about Hypo. Rochefort and his team were ordered to drop their work on the flag officers' code and join in the attack on JN-25b, the latest version of the Imperial Navy code. That change would make all the difference.

 

 

Purple and the Obliging Baron

 

When the cryptanalysts of Friedman's Signal Intelligence Service distributed their replicas of the Purple machine, they could not have imagined that Purple's decrypts of diplomatic traffic would ever throw more than an indirect light on military affairs, especially in Europe. Yet, by an odd twist, Purple decrypts became a vital contribution to military intelligence in the European theater.

The reason for this unexpected cryptanalytic plum was Hiroshi Oshima, the Japanese ambassador to Germany. Both a baron and a general, he was also ardently pro-German. William L. Shirer wrote of him that he was "more Nazi than the Nazis." His strong advocacy of German interests won him the approval of top Nazi officials, including Foreign Minister Joachim von Ribbentrop and Hitler himself. Speaking fluent German, Oshima had hours-long interviews in which Hitler disclosed his innermost thoughts and plans. The Germans took him and his military attaches on tours of German production facilities, defense installations and frontline attack formations. An excellent reporter, Oshima prepared multipage summaries of his observations, which his subordinates encoded on his Purple machine. And of course Allied analysts in Washington and Bletchley read his transmissions almost as quickly as they were decoded in Tokyo.

Moreover, the Japanese reports from Berlin were not the only rich sources of inside information for the U.S. and Britain. The Japanese ambassador in Moscow kept Washington and London advised on their less-than-forthcoming Soviet ally. The ambassador in Rome used his Magic machine to report what he could learn of Mussolini and the Italians. Japanese ambassadors and military attaches in the neutral countries of Switzerland, Sweden, Portugal and Latin America were eager to transmit their findings.

General Marshall said of Oshima's reports that they were "the main basis of information regarding Hitler's intentions in Europe."

As early as January 1941, for example, the baron began informing Tokyo of Hitler's plans to attack the Soviet Union. He tried to persuade Japanese leaders that when this happened they, too, should declare war on the Soviets. Later, he persuaded Hitler to pledge that, in Oshima's words, "if a clash occurs by any chance between Japan and the United States, Germany will at once open war against the United States."

He, Ribbentrop and Hitler liked to get together and dream of the time when Japan would gain mastery over Burma, India and the Indian Ocean while Germany pushed through Ukraine and the Middle East for a linkup in Asia that would presage "a new world order." Oshima's persistence in urging this dream on Tokyo eventually drew a sharp rebuke from a new foreign minister, who let him know that any such idea was completely unrealistic.

Oshima was bold enough to offer criticism to the short-tempered führer. When the Germans did invade Russia and sent in the SS troops to liquidate masses of Russian citizens, he told Hitler what a serious mistake this was. It had turned the conflict into "a war of the peoples" when it could have become a struggle to free the Russian masses from Bolshevism. How much better, he said, if Germany had followed Japan's example in seizing Manchukuo, where they had granted the people a degree of independence that included the formation of a puppet government. How much wiser to have allowed a share of autonomy to Ukraine instead of savagely eradicating masses of its people. His advice fell on deaf ears.

For the U.S. a tragic omission in Oshima's reports was any word about Pearl Harbor. If the Japanese military had let him in on their plans, he would no doubt have wired back that he had relayed this information to Hitler. But since the generals were cagey about what they told the diplomats, there was nothing explicit for Allied eavesdroppers to overhear.

As the war progressed, the Allies learned more about the fighting on the eastern front from Oshima than from the Russians themselves. In March 1943, for instance, the Soviet gave a large Japanese contingent permission to travel across Russia, east to west and then down through neutral territory and on to Berlin. Everyone in the troupe was a spy, eager to gather information as the tour progressed. From Berlin, using Oshima's Purple machine, they reported back to Tokyo—and to Anglo-American analysts—their copious findings on Soviet rail transport, lend-lease aid, and the rebuilding and relocation of factories, oil storage facilities, food resources and the like. They also confided their observations of the solidarity of the people in support of the war. The tone of their reports reflected their awe at the enormous reserves of Soviet manpower and materiel as well as their feeling that the tide had turned against Germany.

Oshima fought against such pessimism. When he realized how the shortages of rubber and other materials were hampering the German war machine, he led the way in establishing the Mutual Economic Aid Pact for Winning the War. Central to this pact were what were called the Yanagi operations, blockade runners carrying vital Far East materials to Germany in exchange for German machinery and sophisticated armaments. Oshima envisioned a steady traffic back and forth that would ease the most urgent needs of both Axis partners. But since the Allies were decrypting his messages as well as those of the Japanese navy, Allied subs knew exactly where to go to intercept and sink the Yanagi ships. The Germans were soon reduced to converting old U-boats in order to transport minimal supplies through the blockade and then abandoned the operation altogether.

Throughout the war, Oshima kept the Allies informed of shifts in the attitudes of Axis leaders. Early on, the partners were wary toward each other about the possibility of one or another splitting off to sue for peace. On December 14, 1941, the baron reported the signing of a war alliance supplement to the Tripartite Pact: it pledged that none of the three Axis powers would negotiate a separate peace with the U.S. or Britain. As for Oshima's pleas that Tokyo declare war on the USSR, in July 1942 Oshima was told unequivocally that there would be no Japanese attack on the Soviets—information that President Roosevelt immediately relayed to Stalin. In the dark days when German armies were plunging deeper into Russia, Churchill and Roosevelt feared that it was the Soviets who would yield to a separate peace. Oshima's messages confirmed that Stalin was holding staunchly against any such temptation. When the tables were turned and the Russians were overpowering the Germans, the baron reported that now it was Hitler who stood adamant against a peace initiative.

It is one of the war's great ironies that the reports of Japan's German ambassador and his consular colleagues were of far greater value to the Allies than they were to their masters in Tokyo.

It seems almost unfair that after all he'd done for them, the Allies after the war tried Oshima as a war criminal and sentenced him to life imprisonment. However, Hitler's Japanese confidant was paroled in December 1955 and granted clemency in April 1958.

Baron Oshima's story adds an incredible extra dimension to the importance of U.S. cryptology during World War II. From the low point of Pearl Harbor, American cryptanalysis swiftly climbed to a dominance that made the plans of Japanese leaders an open book to Allied commanders, while Japan's widespread use of its Purple machine helped extend that dominance to the European conflict. The combined effect was to make the contribution of U.S. intelligence to Allied victory second to none.