By then, a “research desk” had been set up in Room 1645 of Navy headquarters, located in a large, low wooden building along what is now Constitution Avenue. Cryptanalytic offices always have vague names, to disguise their true purpose. The desk was staffed by a small number of people, civilians as well as some naval officers, but the problem for the officers was that paging through codebooks, however helpful to the larger mission, was bad for their careers. This was even truer in the Navy than in other branches of the military. Cryptanalysis is shore duty, an office job. In the U.S. Navy, if you were a career naval officer with any ambition, shore duty was not what you wanted. What you wanted was sea duty and a position as “line officer” and commander. Being a specialist of any sort was not a viable career path. And so officers came and went from the research desk, studying for a couple of years and then shipping out to sea, as their careers required.
It was Agnes Meyer Driscoll who sat perpetually at the research desk, a civilian and a woman and therefore sentenced to permanent shore duty, unlocking the secrets of the naval fleet code that Japan was honing during the 1920s and 1930s. A fleet code is the main system that bases, ships, and organizations use to talk with one another about strategy and tactics, logistics, intelligence, morale, ship movements, situation reports, even weather: anything and everything a commander deems important. Agnes Driscoll studied the stolen codebook day after day, year after year. One of her trainees, Joe Rochefort, later remembered her turning pages with the tip of a pencil eraser, flipping back and forth. She cursed like a—well, like a sailor. She was seen as aloof and sensitive to any kind of treatment that smacked of being patronizing, a trait that Edwin Layton attributed to her discomfort at being a woman so outnumbered by military men. She liked to say that “any man-made code could be broken by a woman.” She and her husband didn’t socialize much, which is a handicap in the prestige-conscious Navy, where men’s careers often are aided by wives who entertain admirals and throw dinner parties.
Even so, the men fetishized her genius. Studying the codebook, never having seen the Pacific Ocean or a single Japanese vessel, Agnes Driscoll became fluent in Japanese ship names and—importantly—cryptographic habits.
She also figured out how the Japanese disguised their fleet code, using a method called “superencipherment” that involves both a code and a cipher. For the main fleet code, the Japanese were using a large codebook containing thousands of three-character code groups that stood for Japanese words, syllables, phrases, and even punctuation marks. Once a clerk wrote out a coded message, he then enciphered each character, somehow, so that the code group would be sent as a different set of characters entirely. The “research desk” knew what the code groups stood for, thanks to the theft of the codebook, but that didn’t do them any good. When they intercepted an actual message, the groups they were looking at had been enciphered. They couldn’t make heads or tails of a message unless they could figure out how to get rid of the encipherment and restore each code group to its original form.
The tiny Navy team—Driscoll, one or two officers, a couple of clerk-typists, a translator—worked for years to achieve this. Joe Rochefort said that the process literally made him sick. It destroyed his appetite and caused him to lose twenty pounds, sitting every day in what he called the “staring process,” smoking everything he could get his hands on: cigars, cigarettes, a pipe. After work he would have to lie down for several hours before he could eat. That the team succeeded he attributed to Miss Aggie—as Agnes Driscoll was called—who discerned that the encipherment was accomplished by transposing or switching the position of the characters.
Successful code breaking often comes down to diagnostics—the ability to see the whole rather than just the parts, to discern the underlying system the enemy has devised to disguise its communications. The Japanese, Agnes diagnosed, were encoding their messages and then using something called columnar transposition, which involves writing the code groups out horizontally but transmitting them vertically, aided by a grid with certain spaces blacked out, whose design changed often. “Mrs. Driscoll was responsible for the initial solution and for most of the solution of the new ciphers and ‘transposition forms,’” said Rochefort, who, as a naval officer, technically headed the desk. The intelligence gleaned provided insight into Japanese fuel supplies, ship accidents, aviation advances, naval maneuvers, and—importantly—strategy for conducting combat operations against the United States. It also revealed that the Japanese were alarmingly well versed in America’s own naval war plan.
Mastering the fleet code was a never-ending undertaking, for the Japanese and for Agnes Meyer Driscoll. As a security measure, the Japanese Navy periodically changed its codebooks—burning the old codebooks, printing new books, and distributing them to every ship, office, and island. When this happened, each word would be assigned a new code group, and the American code breakers would have to start from scratch. Sometimes, the changes were even bigger: In 1931, Thomas Dyer, then a trainee, was puzzling over a new intercept; Driscoll walked up behind him, took his work sheet, looked at it, and said, “The reason you’re not getting anywhere is because this is a new code.”
She was right. The Japanese had changed their system, coming up with code groups that were longer and organized in a tougher, more complex way. Puzzling out the new system took three years, and once again it was Driscoll who did the bulk of the work in cracking one of the most complicated systems ever seen. “Mrs. Driscoll got the first break as usual,” said Rochefort. Her success “was the most difficult cryptanalytic task ever performed up to that date,” Laurance Safford wrote later. When Edwin Layton rotated into the unit, he came to appreciate what he called the “magnitude” of Agnes’s contribution and described it as “spectacular.”
Her feat had enormous real-world impact. In 1936, Driscoll’s efforts revealed that the Japanese had refitted a battleship that now could travel in excess of twenty-six knots. The United States didn’t have a ship that fast, so the Navy upgraded a new class of battleships to exceed that speed. It was a major piece of intelligence and one that justified the entire expense of setting up a research desk. The naval code-breaking office was gradually enlarged, but in 1937, Agnes Driscoll was the only person who knew something about everything. “There is… only one fully trained individual among the permanent force who is capable of attacking any problem,” an official history noted.