The Battle of Midway (Pivotal Moments in American History) (23 page)

Captain Redman’s appointment not only shelved the experienced Safford, it introduced a new tension into the cryptanalytic community. Redman did not know Rochefort or any of the veteran cryptanalysts personally. Perhaps because Rochefort was Safford’s appointee (and not an Academy graduate), Redman was loath to take Hypo’s assessments at face value. Much later, Rochefort recalled, “As long as Safford was in Washington, I just about knew what to expect…. It worked very nicely on a personal basis. It was when other people became involved in it as part of the expansion that we began to have trouble.” In effect, Redman did not trust Rochefort’s judgment enough to be receptive when Rochefort used his intuition to fill in the many blanks in decrypted naval messages. Fortunately, Rochefort found a more sympathetic audience for his assessments in Chester Nimitz. Though Rochefort was under the administrative command of the 14th Naval District and reported officially to Redman in Washington, his mission made him invaluable to CinCPac, and in the end it was Rochefort’s relationship with Nimitz, not the one with Redman, that proved crucial.
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Besides Safford’s dismissal, another change was wrought by the onset of war. On December 17, Rochefort finally received authorization to drop the unprofitable pursuit of the Japanese admirals’ code and join in the common effort to crack the Japanese Navy’s far more widely used operational code, often referred to as the “five-number code.” Nimitz wanted him to pay particular attention to the “deployment of enemy carrier strike forces.” Soon the team in the dungeon began to squeeze bits and pieces of intelligence out of the messages.
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Back in the 1920s, when the Americans first began to pay serious attention to the Japanese naval code, they dubbed it JN-1 (Japanese naval code, version one). Over the years, the Japanese regularly changed their codes, and every time they did so, the American code breakers had to start over again. In June of 1939, the Japanese adopted a new and more complicated system. Since it was the twenty-fifth version of the code, it was dubbed JN-25. Then on December 1, 1940, the Japanese modified that code yet again, and this new variant was labeled JN-25b. It resisted the code breakers right up to the day of Pearl Harbor. When Rochefort’s team received authorization to turn their efforts to this code, they attacked it with a vengeance.
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The JN-25 b code consisted of 40,000 to 45,000 five-digit number groups, such that the messages that went out over the air waves looked something like this:

48933    19947    62145    02943    20382    16380

Some of the number groups were dummies, or fillers, added to confuse the code breakers. In addition to that, however, before sending a message, the Japanese enciphered the code again by using a cipher tablet. The encoder selected a five-digit number from this tablet and added it to the first number group in the message; the next cipher number was added to the second number group, and so on throughout the message. An indicator buried in the message itself revealed the exact location—page number, column, and line—where the cipher number additives could be found in the secondary tablet. Thus the code group for “east” might be 10236, but it would be encrypted again by adding another five-digit number from the cipher tablet. If the encoder added the number 45038, the word “east” became 55264. (Note that in adding the two numbers, there was no carrying: although adding 8 and 6 yields the number 14, only the second digit was used in the product.) To decrypt the message, the recipient needed the initial code book, the secondary code tablet, and the indicator, showing how to subtract the second from the first. The puzzle, in short, was extraordinarily complicated, which is why the Japanese remained confident that their radio messages were secure. In May 1941, when Japanese officials conducted a review of their message security, they concluded: “We need not worry about our code messages.”
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Breaking through these layers of secrecy was tedious. It was helpful that the Japanese ensured that all of the original number groups were divisible by three. The reason for this was to let the recipient know he had subtracted the correct cipher—if the final code number was not divisible by three, he had probably made a subtraction error. Of course, this also allowed the code breakers to know if they were on the right track.

In addition, the volume of message traffic in JN-25 ballooned after the war began, giving the analysts more opportunities to divine the structure of the code. And finally, for a few weeks the Japanese sent messages in both the JN-25 code and the new JN-25b code because some commands had not yet received the new codebooks. This allowed the Americans to compare the messages. Station Cast identified two messages—one that was encrypted and another that was sent out in plain language—that appeared to be identical. It was the Rosetta Stone of naval messages, and it allowed the Americans to verify several of their guesses. Despite that, there were few such “aha!” moments at Station Hypo, and lots of tedious and often unrewarding analysis—plus some educated guesswork.

Because there was a shortage of personnel at Hypo, men frequently worked twelve-hour shifts, or longer. Only about 60 percent of all the messages that were intercepted could be subjected to analysis at all because there were so many messages—five hundred to a thousand every day—and breaking them took time. Of those that were analyzed, fewer than half yielded any useful information, and within those only small fragments, perhaps 10–15 percent, might be rendered comprehensible. Often the code breakers at Hypo could determine the sender and the recipient, and perhaps one or two other phrases. Here, for example, is an actual decrypt from May 5, 1942:

“KAGA and (blank) (blank) less (blank) and (blank) will depart
Bungo Channel (blank) May 4th and arrive (blank) (blank).”

It was Rochefort’s job to fill in those blanks. To say, then, that the Americans were “reading” the Japanese message traffic is an exaggeration. After much hard work, they might in the end be able to decipher a tiny fraction of it, and they had to rely on their experience, informed guesswork, and intuition to determine what it might mean and how to take advantage of it.
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Rochefort and his team worked long hours and with great intensity. Unable to tell whether it was night or day in their windowless quarters, they ignored the clock and often worked all night. It was routine for many of them to work twenty hours or more per day. Even the “roofers” worked watch and watch: twelve hours on, twelve hours off. One member of the Hypo team, Lieutenant Jasper Holmes, later wrote, “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.”
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Because air conditioners were needed to protect the IBM machinery, it was cold in the Dungeon. Ensign Donald Showers recalled later that “it was cold as hell down there.” To ward off the chill, Rochefort often wore a maroon-colored corduroy smoking jacket over his uniform. To protect his feet from the hard concrete floor, he wore slippers. This has led some to conclude that he was highly eccentric. In the 1976 film
Midway
, Hal Holbrook portrayed him as a kind of cheerful goofball. In fact, Rochefort, by now a full commander, was a serious-minded and entirely professional naval officer. Asked about the smoking jacket after the war, he replied simply, “It was a practical matter, and I was just cold.” He often slept on a cot in the Dungeon instead of heading back to his lonely quarters. (His family had been evacuated back to California.) In part, his intensity derived from the nagging sense of guilt—that if only he had had access to the JN-25 intelligence before December 7, he might have been able to predict the raid.
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At his desk, Rochefort laid out the pieces of message traffic that he or someone else on his team had been able to decrypt. “You see a whole lot of letters and a whole lot of numerals, perhaps in the thousands or millions,” Rochefort recalled after the war, “and you know that there is a system in there, and there’s a little key to the system that’s something real simple, and you just keep after it until you finally solve it.” Another team member recalled, “We went over the papers one by one, we went through the whole compilation of traffic analysis, how each command, or unit, became associated with others.” Eventually, by matching number to number, phrase to phrase, and unit to unit, Rochefort could begin to assamble a bigger picture. One officer likened it to being able to visualize the overall pattern of “a Virginia reel or square dance.”
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For several weeks after Pearl Harbor, Rochefort and Hypo confined themselves to providing raw data about fleet movements and communications activity, the result, perhaps, of their intense disappointment that they had failed to predict the raid. Then in January, 1942, Rochefort noted that several of the messages he and his team were working on contained the code group that he believed stood for
koryaku butai
(invasion force), and that some of those same messages also contained the letters “RR,” which he believed stood for Rabaul. (In the Japanese system, all geographic locations were assigned a two- or three-letter code.) Based on that, and the overall pattern of message traffic, Rochefort predicted that the Japanese would invade Rabaul in the third week of January. When the Japanese went ashore there on January 23, it seemed proof of Rochefort’s ability to produce substantial intelligence out of a few scraps of radio traffic, and it helped lay the groundwork for a partnership of trust that soon emerged between Hypo and CinCPac—that is, between Rochefort and Nimitz.
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Lieutenant Commander Edwin Layton was Chester Nimitz’s intelligence officer. Layton briefed his boss every morning at five minutes to eight, passing along whatever information the Hypo team had managed to cull from the airwaves. (U.S. Naval Institute)

The man who acted as the liaison in that partnership was Edwin Layton, a 39-year-old lieutenant commander with dark curly hair, thick glasses, and prominent ears. He looked more like a high school math teacher than a naval officer. After graduating from Annapolis in 1924, Ensign Layton had been assigned to escort a group of visiting Japanese naval officers around San Francisco, and he was surprised to discover that they all spoke perfectly colloquial American English. He wondered how many American naval officers spoke Japanese, and when he learned that the answer was none, he wrote to the Navy Department, deploring this fact and volunteering to become the first. At the time, Navy regulations stipulated that in the entire U.S. Navy, only two officers at a time could be assigned to language studies, and, in any case, no one could apply for it until he had completed five years of sea service. Five years later, after serving aboard the battleships
West Virginia
and
Pennsylvania
, Layton applied again. This time he was accepted. While crossing the Pacific en route to Tokyo for his new assignment as a Japanese-language officer, he met another young officer bound on the same mission. It was Joe Rochefort.
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