Overlooked No More: Marthe McKenna, Nurse Who Spied for the British in World War I

As a nurse in a German military hospital in occupied Belgium during World War I, Marthe McKenna spent her days saving the lives of German soldiers. All the while, she secretly helped the British plot attacks against them.

McKenna, who was Belgian, spied on the Germans for almost two years starting in early 1915, using her position to observe them and gain their trust.

“Because I am a woman I could not serve my country as a soldier,” she said in her memoir, “I Was a Spy!” (1932). “I took the only course open to me.”

“I Was a Spy!” told of harrowing missions and narrow escapes. Much of the account was later determined to be invented, but the book captivated audiences in Britain. “Her tale is a thrilling one,” Winston Churchill wrote in the introduction. “Having begun it, I could not put out my light till four o’clock in the morning.”

McKenna described passing coded messages about the movements of German troops, helping Allied prisoners escape when they were brought to the hospital and even disguising herself as an injured German soldier to gather information about intelligence leaks.

Sometimes, McKenna wrote, she would pass information to other Allied spies who were known to her, and sometimes she would simply slip messages through a window as “a hand — white against the darkness — came out.”

At the same time, McKenna’s multilingualism and nursing skills became so indispensable to the Germans they awarded her the Iron Cross, a military decoration that she said ultimately saved her life.

Marthe Mathilde Cnockaert was born in October 1892 in Westrozebeke, Belgium, one of five children. Her parents, Félix and Marie-Louise, were farmers before the war.

The Germans’ invasion of Belgium in 1914 interrupted McKenna’s medical studies at Ghent University. She began working at a makeshift hospital in Westrozebeke set up by nuns, treating both German and Allied soldiers. In early 1915, she and her family relocated to Roeselare, a small city in Flanders, Belgium, where she began working in the German military hospital.

It was there, McKenna wrote, that the British called on her. She describes how a family friend named “Lucelle” recruited her, but according to Gilbert Coghe, an author and historian from Westrozebeke, this was the code name for her aunt, Maria Deroo, who was already working for British intelligence.

McKenna agreed to become a spy out of patriotism, she wrote, “to defeat such an abhorrent machine, which is attempting to overrun our beloved land.” But the nature of the work often horrified her. In one mission, she describes flirting with an officer who worked at the train station to learn when munitions would be delivered to the German front. She was successful, and the British sent planes to shell the station.

When it dawned on McKenna that the officer would likely be in danger as a result, “for a moment ghastly terror shook me in every limb. Was I — quiet, harmless Martha Cnockaert — really about to do this terrible thing?” (The book uses the English spelling of her first name.)

McKenna said she was eventually caught after she aided in the explosion of a weapons stockpile. She lost a wristwatch engraved with her initials at the scene and the Germans, suspecting the owner of the watch to be the culprit behind the explosions, put up a notice saying they had found it. She fell into their trap and claimed it.

They searched her home and found hidden coded messages, and she was arrested on espionage charges in November 1916. Though the penalty for spying was usually execution, McKenna said she was spared and imprisoned instead because of her work as a nurse and the Iron Cross she had received.

Later, McKenna received honors from France and Belgium. She was hailed in dispatches to England by British Field Marshal Sir Douglas Haig, who made a list of Belgians who had provided “distinguished and gallant services.”

After the war, she married John McKenna, a British officer, and they moved to England. Historians believe her husband was likely the ghostwriter for “I Was a Spy!” though publicly the couple claimed Marthe McKenna wrote it. The book sold about 200,000 copies when it came out and received rave reviews.

“From first page to last it is a thrilling, breathtaking book,” The New York Times wrote. The Sunday Dispatch in England printed excerpts, describing the book as the “greatest of all war stories” and comparing McKenna to Joan of Arc. But how much of it is true remains a question.

Coghe, the historian, said many parts of the book were fictionalized and that some events combined McKenna’s experiences with those of her aunt.

Churchill wrote in the introduction that, “I cannot, of course, vouch for the accuracy of every incident; but the main description of her life, intrigues, and adventures is undoubtedly authentic.”

The memoir was adapted into a well-received movie of the same name in 1933.

In the two decades that followed, McKenna and her husband released more than a dozen other books, mostly spy novels. One of them inspired the film “Lancer Spy” in 1937. The books and movies made McKenna a celebrity in the United Kingdom, where she attended movie premieres and toured to promote her books.

McKenna and her husband moved back to Westrozebeke around 1947. He left her for another woman some time in the early 1950s, Coghe said, about the time the spy novels stopped being published. McKenna lived largely in isolation until her death, around 1966.

She had no children.

Despite her fame in England, McKenna had been largely forgotten in Belgium until recently. In 2000, a biography about her led to the first Dutch translation of “I Was a Spy!” In 2016, as part of ceremonies commemorating the war, an interactive exhibition throughout the city of Roeselare featured McKenna as a character. In it, she helped guide participants who were pretending to be spies.