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 Japanese 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 next matched when Rowlett's team reconstructed PURPLE in 1940 under far better-resourced conditions. Despite this, recognition came only long after her death. She died on 16 September 1971; the NSA/CSS inducted her into its Cryptologic Hall of Honor in 2000, twenty-nine years later.
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 differenced (non-carrying subtraction) to yield the difference of two code 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. She never held flag rank or formal command authority; she held intellectual authority instead, and it proved more durable.
- National Cryptologic Foundation — Agnes Meyer Driscoll ↗ (death 16 September 1971; NSA/CSS Cryptologic Hall of Honor, 2000)
- Naval History and Heritage Command — “Agnes Meyer Driscoll: The First Lady of Naval Cryptology” ↗
- Holtwick, Jack S. Pearl Harbor Revisited: U.S. Navy Communications Intelligence, 1924–1941 (NSA Center for Cryptologic History) — the declassified internal history of OP-20-G in which Driscoll’s Red Book, Blue Book and M-1 work is documented ↗
- Carlson, Elliot. Joe Rochefort’s War (Naval Institute Press, 2011) — Driscoll as Rochefort’s instructor ↗
- Indiana University, Center of Excellence for Women & Technology — Agnes Driscoll profile ↗
- Wikipedia — Agnes Meyer Driscoll (encyclopaedia overview) ↗
Removed as unsourced: a claim that the first serious historical account of her work appeared in 1995. No work of that year appears in any source consulted, and the NCF lists the Kevin Wade Johnson studies undated. The documented recognition record has been used instead. An FDR anecdote was removed from this page in the same pass.
| 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 |