Code Girls


written by Alan R.

In the years leading up to and during World War II, increasing usage of radio and telegraphic transmissions to send secret communications necessitated the need for ciphers to disseminate sensitive information, such as military planning and operations. As the ability of one force to crack the enemy’s codes improved, the requirement for elevated sophistication of code generation became essential. This landscape eventually evolved into using machines to create ciphers, typically with moving parts and electromechanical rotors. These devices became so complex that their outputs mandated a complete recreation of the machines themselves if a codebreaker wanted to read an enemy communique. This process was extremely labor-intensive since computers did not yet exist.

The Allied Forces invested heavily in cracking codes made by the machines of the Axis Powers. The most famous apparatus was the Enigma machine, used by the Germans, which was ultimately solved by Polish intelligence experts.

The Enigma I machine - photo by Alessandro Nassiri

In previous Woman Crush Wednesday articles from The Mountains Are Calling, I have been amazed by the incredible achievements and contributions to life, culture, science, and technology by women. Once again, related to today’s topic of cryptology and national security in times of war, we have clear evidence of the monumental additions by women.

At the beginning of World War II, more than 11,000 American women joined WAVES – Women Accepted to Volunteer Service – for the purpose of deciphering communications between enemy forces and developing methods to ensure the security of Allied dispatches. The transmissions on both sides ranged from routine messages to military operations to logistics. Synergizing the information gathered from these sources often painted a picture of enemy activity and planning, which was crucial for successful responses. The work was tedious, but cryptographic breakthroughs yielded the ability to provide protection for Allied forces by anticipating enemy actions.

Today, we highlight two pioneers in cryptology prior to and during the Second World War.

Agnes Driscoll - photo from National Cryptologic Museum/NSA

Agnes Driscoll’s military service began in 1918, toward the end of World War I. She enlisted in the Navy, joining the Code and Signals Section. She possessed ideal qualifications for cryptology, holding a bachelor’s degree in mathematics and physics, while proficiently speaking English, French, German, Latin, and Japanese (Editor’s note: Driscoll studied at Otterbein College and the Ohio State University, both proximal to TMAC HQ!).

During the interregnum between the World Wars, the Japanese developed a series of communications systems using an operational code known as the “Red Book.” Agnes Driscoll became the primary codebreaker for this method and several other Japanese Naval codes. She provided the United States with important intelligence on the planning and execution of naval maneuvers, in addition to the Japanese strategies to defeat and exploit our own coding weaknesses. This knowledge enabled the US to make appropriate adjustments.

The Japanese, of course, continued to refine and improve their techniques, which we persisted to decode until they developed machine-based ciphers. Aggie’s early successes laid the foundation for the Allied capability to crack mechanically generated ciphers, as the US entered World War II.

Many pre-war Japanese codes were broken mathematically with pen and paper; machine code required more refined methods.

Enter Genevieve Grotjan.

Genevieve Grotjan - photo from NSA

Grotjan earned a degree in mathematics, yet, inexplicably, could not find a position as a teacher in early 20th-century America. So, in the late 1930s, she entered the military as a cryptologist for the Army’s Signals Intelligence Service (SIS) and built upon Driscoll’s work.

Less well known than Enigma, but potentially as important, was a Japanese code, called “Purple Machine” by the Allies. As the Japanese continued to develop more complex machines and codes during the war, the Allies appended different colors to their internal references. “Purple” was the most sophisticated and difficult code to crack, used by the Japanese between 1939 and 1945 to transmit diplomatic messages.

Allied codebreakers spent 18 months trying to solve the cipher. In late 1940, Grotjan began to notice patterns, repetitions, and cycles in the encrypted missives, which ultimately led to its resolution. As a result of her achievement, the SIS recreated the machine used by the Japanese to crank out the code. The importance of Grotjan’s discovery cannot be overstated. The Japanese continued to utilize the Purple Machine until the end of the war, apparently believing its integrity to be intact. Grotjan’s solution in 1941 provided four years of free intelligence! Not until the end of the war did the Japanese realize their communications had been compromised.

Grotjan’s success led directly to several strategic victories. The decoded messages helped decisively win the Battle of Midway; they also allowed the Navy to track and down a plane carrying the Japanese Admiral Yamamoto, leading to his death. These two instances had a dramatic effect on World War II.

The replicated Purple Machine, on the right - photo from US Army

Most of the 11,000 cryptologists involved in WAVES remain criminally unrecognized. Their individual and combined efforts resulted in countless intelligence triumphs, helping pave the way for an Allied victory.

Agness Driscoll and Genevieve Grotjan are but two of the outstanding women whose mental gifts undoubtedly saved many lives during the World Wars. Perhaps the thousands of others each deserve individual examination, but a grateful nation can, at the very least, recognize them as a collective.

On behalf of the scores of WAVES cryptologists, we welcome Driscoll and Grotjan to the Hallowed Halls of Woman Crush Wednesday at The Mountains Are Calling.

Further Reading and Exploration

Code Girls: The Untold Story of the American Women Code Breakers of World War II by Liza Mundy

Interview with Liza Mundy – The National World War II Museum

Pioneering Women in Cryptology – National Air and Space Museum

WWII Women Cracking the Code – National Air and Space Museum

Agnes Meyer Driscoll – NSA

Genevieve Grotjan Feinstein – NSA

Women Cryptologists of World War II Stamps – USPS

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