This new Japanese machine had the same letter-changing mission, but nobody knew how it worked. No Westerner had laid eyes on it, or even a facsimile or prototype. The machine was not as mobile as the Enigma—not mobile at all. Unlike Enigma, it ran on electrical current and needed an outlet it could be plugged into. Only the most important Japanese embassies were given access to it—those in Washington, Berlin, London, Paris, Moscow, Rome, Geneva, Brussels, Peking, and a few other major cities.
A machine ciphering system worked well for diplomats. In the 1930s, phone calls were costly and vulnerable to being tapped. The foreign office in Tokyo often needed to send the same message to all its far-flung ambassadors, and rather than pick up a phone and make the same call, over and over, it was easier to craft a message and hand it to a clerk, who would write it out in Romaji, a phonetic version of Japanese that used roman letters to spell out the syllables, as in ma-ru, for merchant ship. The clerk would run “maru” through the machine, producing a new stream of letters—say, “biyo”—that could be cabled. The enciphering mechanism could be set in different positions, according to a key, or setting. The machine could be used in either enciphering or deciphering mode, so the diplomats could use their own machines to restore the message to its original meaning. They also could use it to write back to Tokyo.
The Japanese diplomats were, of course, discussing their country’s war plans. They also were meeting with Hitler, Mussolini, and other key Axis leaders. If the Americans could uncover the machine’s workings, they would have access to a priceless stream of insight, gossip, and strategy, involving not only Japanese intentions but those of every tyrant in Europe.
But cracking the Japanese machine was proving elusive. By the time that Genevieve Grotjan was assigned to the project, the Americans had been struggling for months. The first message in the new machine cipher had been intercepted in March 1939, emanating from the Japanese embassy in Warsaw. The code breakers had known it was coming thanks to the fact that they had broken a simpler machine cipher that the Japanese used for much of the 1930s. The Japanese referred to the first machine by the prosaic name Angooki Taipu A—Cipher Machine Type A—and so this new one was called Angooki Taipu B. The Americans called the first one Red and the second one Purple. Purple didn’t work the way Red did. It was more complicated, which was why the code breakers were having such trouble with it.
The small number of Westerners who knew about the existence of the Purple cipher thought the Americans in William Friedman’s tiny Japanese unit were wasting their time. The British had tried to break the Purple machine—as had the Germans—but both abandoned the job as undoable. The U.S. Navy, in the wing next door, worked on Purple for four months but decided to concentrate on JN-25. William Friedman’s group of civilians were the only ones who refused to give up, or were temperamentally incapable of doing so.
The men Friedman had hired in 1930 had benefited from years of training. Now, with war raging in Europe and Asia, and America’s involvement looming—ever since the fall of France, it had become inevitable—new hires like Genevieve Grotjan were flung directly into the work. Frank Rowlett, the southerner, was supervising the Purple effort. He was a big man, friendly, and tended to play up his rural-boy persona as a way of masking his strategic intelligence and competitive instincts, saying things like, “I’m just a country boy from the sticks, but…” Grotjan found him personable and easy to work for.
As he built his team, Friedman had scoured the civil service rosters. The kind of person he wanted was hard to define. He sought intelligence but also persistence. Though a penchant for crossword puzzles is sometimes seen as an indicator of code-breaking talent, Friedman scoffed at the idea that breaking codes is truly akin to solving newspaper crossword puzzles. Crossword puzzles are easy; once you get a clue, you feel spurred on, you feel encouraged. Small victories and incentives are built in. Crossword puzzles are designed to be solved, while codes and ciphers are designed to prevent solution. With codes, you have to be prepared to work for months—for years—and fail.
In September 1940, failing was exactly what they seemed to be doing. After more than a year of frustration, the only thing the code breakers knew for sure was this: One weakness of the Japanese Purple machine stemmed from the fact that Tokyo had been a little too eager to save money. In the 1930s, when Japanese cryptographers were designing the earlier Red machine, messages often were transmitted in groups of four or five letters. Groups that could be pronounced were cheaper to send. (Friedman attended the conferences where telegraph companies in different countries laid down rules of the road like these, coordinating things like costs and structure and allocation of frequencies.) To be pronounceable, a five-letter group had to contain at least two vowels. The Red machine therefore transformed vowels into vowels, and consonants into consonants, to ensure that “marus” ended up as something like “biyav” and not, say, “xbvwq.” That way, the messages remained pronounceable.
Friedman’s team had figured out that the old Red machine employed two mechanisms to achieve this, one of which transformed the six vowels, the other the twenty consonants. They referred to these mechanisms as the “sixes” and the “twenties.” The Friedman team had managed to build a facsimile of the Red machine, using Western parts. Their facsimile worked so well that Friedman’s code breakers often were able to decipher a Red message and deliver the contents to U.S. military intelligence before the Japanese code clerks had gotten the same message to their own bosses. When the Red machine began to go off-line, in 1939, American officials found it frustrating to be deprived of the fruits they had become accustomed to enjoying.
By the time the Purple machine came along, cable companies had relaxed the rule about groups needing to be pronounceable, so there was no need for sixes and twenties. Even so, new systems often contain elements of older ones: This is known as “cryptographic continuity.” Banking on this, the code breakers hypothesized that the Purple machine also used two mechanisms, one that transformed six letters—any letters, not just vowels—and one that transformed twenty. Sure enough, when the Purple intercepts started appearing, Friedman’s code breakers were able to see that six letters appeared more often than others. But the twenties were the stumbling block. No matter what kind of system they conjectured, the Americans could not discern how the remaining twenty letters were enciphered.