Agnes Meyer Driscoll
"Miss Aggie" was the Navy's preeminent cryptanalyst for thirty years — breaking Japanese fleet codes that no one else could touch.
Agnes Meyer Driscoll
Agnes Meyer Driscoll was an anomaly: a woman with formal training in mathematics, physics, and four languages who joined the Navy as a "yeomanette" in 1918 and never left. Assigned to OP-20-G — the Navy's radio intelligence division — she broke the Japanese Red Book naval code in 1926 and the Blue Book in 1930, giving the U.S. Navy crucial advance intelligence about Japanese fleet doctrine and operations. In 1935 she broke the Japanese M-1 cipher machine (also called the "Orange" machine), an electromechanical device considered unbreakable by the Japanese, purely by hand analysis. Her methods for attacking machine ciphers directly influenced Joe Rochefort's team at Station HYPO and shaped every American cryptanalytic program until the war. She spent three years in WWII unsuccessfully attacking the Naval Japanase JN-25 codes — the problem eventually solved by others with IBM punch-card machinery. She retired from NSA in 1959 after 41 years of service, having trained the majority of the Navy's senior cryptanalysts.
Why This Person Matters
Agnes Driscoll is the founding figure of American naval cryptanalysis. Every break that mattered in the Pacific — JN-25, the Imperial Navy's operational codes, Station HYPO's contribution to Midway — traced its institutional lineage through her training programs, her methods, and the analysts she mentored. Joe Rochefort, who led the Pearl Harbor code-breaking effort, was her student. Tommy Dyer, who ran the analytical section at HYPO, was her student. She broke the Japanese M-1 cipher machine by hand long before Americans had their own cipher machines to attack, using pure mathematical analysis — a feat that was not replicated until Bletchley's Colossus team attacked Lorenz a decade later under far better-resourced conditions. Despite this, she received no public recognition until long after her death. The first serious historical account of her work appeared in 1995; she had been dead for 24 years.
The Japanese Navy used a series of codebooks to encrypt operational communications. The "Red Book" (JN-1), used from 1918 to 1930, was a two-part code with 100,000 entries. Driscoll recovered it by 1926 through a combination of traffic analysis and crib techniques — identifying fixed phrases in message headers and exploiting the limited vocabulary used for weather and routine naval dispatches. The successor "Blue Book" (JN-4/5) was more complex, with additive key superencipherment on top of the base code. Driscoll broke its additive tables by 1930, again largely through depth attacks — messages sent in the same additive key position, where the two ciphertexts could be XOR'd to produce the sum of two plaintext groups, which could then be solved by guessing probable words. These techniques became foundational doctrine for American signals intelligence.
The Japanese M-1 cipher machine (also known as the Type 91 Printing Telegraph, or "Orange machine" in US parlance) was an electromechanical device using drum rotors to generate polyalphabetic substitution. It was introduced in 1931 for high-level naval attaché communications. Driscoll attacked it without any captured hardware using purely traffic analysis and algebraic techniques: she identified the cycle lengths of the rotors from ciphertext alone, determined the wiring from depth exploitations, and recovered daily keys for extended periods of traffic. American officials were so surprised by her success that they initially assumed she must have bribed someone for physical access to the machine. She had not: the break was entirely analytical. The methodology she developed was later applied by Frank Rowlett to PURPLE.
Perhaps Driscoll's least visible but most consequential contribution was institutional: she spent decades teaching Navy cryptanalysts. In an era when cryptanalysis had no formal curriculum anywhere in the world, she developed training programs for OP-20-G from scratch. Analysts who passed through her training in the 1920s and 1930s went on to lead the most important cryptanalytic operations of WWII. The overlap between her students and the key figures at Station HYPO, OP-20-G's Pearl Harbor outpost, was near-total. When President Roosevelt asked in 1942 how the Navy would replace the Pearl Harbor losses in cryptanalytic capability, the honest answer was that the training pipeline Driscoll had built over twenty years was already producing the answer. She never held flag rank or formal command authority; she held intellectual authority instead, and it proved more durable.
| Born | July 24, 1889, Geneseo, Illinois |
| Died | September 16, 1971, Washington, D.C. |
| Education | Ohio State — BA Maths, Physics, Languages |
| Service | OP-20-G / NSA, 1920–1959 |
| Key breaks | Red Book (1926), Blue Book (1930), M-1 (1935) |
| Notable student | Joe Rochefort (Midway) |
| Award | Navy Meritorious Civilian Service |