None of this, of course, helped the Americans predict the attack on Pearl Harbor, and after December 7 it seemed to many that a housecleaning was in order. Just as Kimmel was shoved aside in Hawaii, Safford was replaced at OP-20-G by Captain John R. Redman. A member of the Naval Academy class of 1919 who had graduated early for service in World War I, Redman had excelled in athletics. A standout on the football and lacrosse teams, he was also captain of the wrestling team, a sport in which he competed at the 1920 Olympic Games in Antwerp, finishing fourth as a light heavyweight and just missing an Olympic medal. Redman had a strong personality and long service as a communications officer in cruisers and battleships, but no real experience or expertise in code breaking. In fact, his prime qualification for his new job may have been that his older brother, Rear Admiral Joseph R. Redman, was the director of Naval Communications.
Captain John Redman, seen here as a rear admiral in a postwar photograph, headed up the intelligence office in Washington (OP-20-G) and was often suspicious of Rochefort’s analysis. (U.S. Naval Institute)
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.8
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.9
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.10
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.”11
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.12
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.”13
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, Rochef
ort, 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.14
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.”15
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.16
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.17
While in Japan, Layton and Rochefort studied not only the language but also the culture. After the few hours of formal classroom study, they went out into the streets to strike up conversations. “I was most interested in why [the] Japanese do certain things they way they do,” Layton recalled, “why they think the way they do—why they approach a problem the way they do.” What both men learned was that in Japanese culture, as well as in their language, “there is more nuance than directness.” Even if the words were clearly understood, they might not reveal the true meaning of any given statement.18
Layton went back to sea in 1939 as the commanding officer of the destroyer-minesweeper USS Boggs, but in February of 1941 he was assigned to Kimmel’s staff as his intelligence officer. After Nimitz took over as CinCPac, he told Layton, “I want you to be the Admiral Nagumo on my staff, where your every thought, every instinct, will be that of Admiral Nagumo’s; you are to see the war, their operations, their arms, from the Japanese viewpoint and keep me advised about what you (as a Japanese) are thinking.” Of course it was not Nagumo that Layton should have been channeling, but Yamamoto. Nagumo, as we have seen, was merely a link in the chain, and not a particularly imaginative one. Yamamoto was the prime mover. Still, Layton got the idea. It was his job not only to monitor whatever fragments of information Rochefort’s hard-working team was able to glean from the Japanese message traffic but also to draw conclusions about what they meant as well. Soon a regular routine evolved in which Rochefort talked to Layton, often several times a day, on a secure phone line, summarizing what he had found and what he thought it meant, and then Layton would go see Nimitz.19
Layton briefed Nimitz every morning at precisely five minutes to eight. If a message came in that suggested a special urgency, Rochefort would call Layton or send a messenger to his office. If it was something of particular significance, Layton would go to fleet headquarters early or, more rarely, show up in the middle of the day. When that happened, Nimitz would interrupt whatever he was doing to see him. In effect, Rochefort was the cryptanalytic scientist doing the lab work in the Dungeon; Layton was the spokesman whose job it was to convince Nimitz to trust Rochefort’s conclusions. In Australia, the head of Station Cast, Lieutenant Rudolph Fabian, provided similar intelligence briefings for Admiral Leary and General Douglas MacArthur, yet without the kind of mutual trust and confidence that emerged in Hawaii.20
One problem in the command relationship was that technically Rochefort did not work for Nimitz but for the Commandant of the 14th Naval District, and he reported to Redman in Washington, where a new office called Combat Intelligence (OP-20-GI) was supposed to collect the data and do the analysis. Layton, who was on Nimitz’s staff, was not in this chain of command. But because Rochefort and Layton were such good friends, based on their years together in Japan, there was a strong sense of partnership to their efforts. Then, too, Rochefort believed that he was uniquely placed to provide both the raw data as well conclusions about what it meant. “I felt that I had the knowledge and experience of being able to estimate and form a judgment on what [the] traffic actually meant,” he said later. “I was in a better position to say what they meant than anyone else.” As a result, the Layton-Rochefort partnership effectively bypassed Washington and took intelligence estimates directly to the theater commander, a practice that Redman increasingly deplored and resented.21
The unrelenting work schedule yielded results. In February the team at Hypo achieved a kind of breakthrough, and soon they were filling in many more blanks in the Japanese message traffic. By April, they were often able to intercept, decrypt, and translate Japanese messages within hours of the original transmission. On April 5, three days before Halsey and the Enterprise left Pearl Harbor to join the Hornet en route to Tokyo, Rochefort was working on an operational message that had been sent from Combined Fleet headquarters at Hashirajima. It was addressed to the aircraft carrier Kaga, still undergoing repairs at Sasebo. One number group in the message stood out. Rochefort had already determined the code for “invasion group,” and now he saw that code used in close association with the letters “MO.” Rochefort suspected at once that it referred to Port Moresby. The Japanese had used a variety of other geographical designators for Moresby, including RZ, RZQ, and RZP, and all of these had appeared with increasing frequency in messages from Inoue’s Fourth Fleet. Now, with this new intercept, Rochefort concluded t
hat the Japanese were planning an invasion that would involve the Kaga and at least one other carrier, initially misidentified as the Ryūkaku, though it subsequently proved to be the small carrier Shōhō.22
Rochefort called Layton on the secure phone and told him that he had “a hot one,” and that he was sending the raw decrypt over by messenger. “It looks like something is going to happen,” Rochefort told him, “that the man with the blue eyes will want to know about.” When the courier arrived, the many blanks in the message left its meaning ambiguous to a nonexpert. Though it was clear enough to Rochefort, anyone not versed in reading such messages would conclude that it was hardly a smoking gun. Over the next several days, however, more clues arrived. All that week, the men of Station Hypo focused on the growing pile of evidence that the Japanese were about to launch an offensive through the Coral Sea to Port Moresby. Holmes recalled that “the chart desk was strewn with charts of New Britain, New Guinea, and the Solomon Islands.” After the British station in Colombo, Ceylon, intercepted a message that referred to special orders for Carrier Division 5—the Shōkaku and Zuikaku—Rochefort’s team studied the traffic for any reference to those two carriers. “Each incoming message was quickly scanned for references to [Inoue’s] Fourth Fleet or Carrier Division 5,” Holmes recalled. “We lived and breathed and schemed in the atmosphere of the Coral Sea.”23
The Battle of Midway (Pivotal Moments in American History) Page 16