The Secret Cryptographer - OZY | A Modern Media Company
Joan Clarke


Because World War II history is still leaving out some of its most important female movers and shakers.

By Jack Doyle

No puzzle was too complex for Joan Clarke. So when war gripped Europe in 1939 and she found herself trapped in a world of contradiction, Clarke found a way out. 

She had just graduated with top marks in mathematics from Cambridge University, but she couldn’t get her degree. Britain was mobilizing for war, but she couldn’t join the fight. So while her male colleagues collected their diplomas and uniforms — Cambridge didn’t award degrees to women until 1948 — Clarke decided to head underground. 

The native Londoner would become a combatant in World War II’s biggest clandestine battle: the race to break the Nazis’ impenetrable code. During the war, Clarke would join the world’s greatest minds, with mathematician and father of the modern computer Alan Turing asking for her advice and relying on her input. She would go on to help turn the tide of war by literally doing the “impossible.” But today, very few know her name.

Knowing how dangerous Enigma was, the British put a call out for the nation’s best and brightest.

The Enigma code, invented in Germany shortly after World War I, represented one of the Allies’ biggest challenges. Using small, portable electrical machines with rotating wheels, the Nazis scrambled messages via a complex system of letter substitution. To an untrained eye, Enigma-coded messages appeared to be a meaningless jumble of letters. But with the help of an Enigma machine, U-boat commanders, spies, pilots and Nazi government officials could effortlessly communicate crucial information about military movements and plans of attack.

Knowing how dangerous Enigma was, the British put a call out for the nation’s best and brightest. Modern code-breaking was still an uncertain art, so the Government Code and Cypher School discriminated less when recruiting, pooling from chess champions, foreign nationals and — perhaps most boldly — young women.

And so Clarke entered the mysterious world of Bletchley Park, the British government’s secret headquarters dedicated to cracking the uncrackable code. When Cambridge mathematics don Gordon Welchman was asked who might fit the bill for the formidable task of cracking Enigma, he didn’t hesitate. His best student was 23-year-old Clarke.

Bletchley Park

During World War II, Allied cryptographers at Bletchley Park broke a large number of Axis codes and ciphers, including that of the German Enigma machine.

Clarke’s obvious gift for logic helped her stand out. Struggling with low pay, discrimination and exclusion from Bletchley’s darkest secrets, she nevertheless earned a promotion that put her in the line of fire. Bletchley Park was, by all accounts, a strange and intimidating place. For Clarke, a shy middle-class girl used to keeping her head down around rowdy Cambridge boys, it was a bit of a culture shock. Bletchley employed eight women for every one man, but the men made significantly more money and worked more closely on cracking the code, leaving the women to smaller, less secretive clerical tasks.

She began a new job at Hut 8 cracking the naval Enigma, the key to the deadly U-boat force’s movements and plans. Joining her were some of the finest minds of the century, including Turing. As they worked frantically to crack the code, often staying well past working hours, Clarke and Turing developed a powerful bond. 

Sadly, this is the part history remembers most — Clarke was briefly Turing’s fiancée, doomed to rejection when he revealed his homosexuality shortly after proposing. But in reality, Turing fiercely depended upon Clarke as a friend and esteemed colleague. During work hours, they struggled with the same data and bounced ideas off each other; off-duty, they played chess and talked over the day’s problems.

Joan Clarke

Joan Clarke

Clarke’s quiet exit from wartime life also, in part, explains her relative lack of renown. Though she was decorated for her services in cracking Enigma, the public would not learn of her achievements for decades. In 1954, few people knew about her connection to the famed Turing, when he committed suicide after undergoing court-ordered chemical castration for his homosexuality.

Clarke seems to have been happy to settle down into a quiet married life working on mathematics and history. She became an expert in rare Scottish coinage and later returned to work for the Government Communication Headquarters in the 1960s. Secrecy laws prevented her from divulging details of her wartime accomplishments, but they don’t explain why she’s been edited out of fictionalized portrayals of Bletchley Park.

This will soon change with Keira Knightley’s portrayal of her in the upcoming Bletchley film The Imitation Game. But the Hollywood star has warned that it isn’t a true-to-life documentary — meaning Clarke’s personality has been altered to appeal to a modern audience.

Clarke, who died in 1996, deserves more recognition in her own right as a woman who helped defeat the Nazis.


Sign up for the weekly newsletter!

Related Stories