Marthe Cnockaert: The Lady Double Agent of WWI

Marthe Cnockaert: The Lady Double Agent of WWI

Shannon Quinn - July 3, 2018

Marthe Cnockaert was living in Westrozebeke, Belgium with her parents and brothers in 1914 when she learned the world was going to war. Her brothers went off to serve in The Great War, which would later be known as World War I. Marthe secretly wished that she could do something to fight for her country, as well, but women were not allowed to serve in the armed forces. It didn’t take long for the Germans to occupy Belgium, and locals were trying to defend their land at all cost.

Marthe Cnockaert: The Lady Double Agent of WWI
Portrait of Marthe Cnockaert. Credit: Wikimedia Commons.

German soldiers accused her father of trying to shoot at them. This was not uncommon. Roughly 1,000 Belgian civilians shot at German soldiers when they invaded their villages, and it was taken very seriously. They wanted to demonstrate that the would not tolerate civilian intervention in the war, so they burned down the Cnockaert family home. While she was able to escape with her parents, they were left homeless, surrounded by the enemy.

A kind neighbor let them stay in their home, and Marthe’s father decided to move to a nearby town called Rousseliere to work and earn some money to they could find another place to live. Marthe and her mother stayed behind in Wstrozebeke. She decided to become a nurse at the local hospital, where she treated both Belgian and German soldiers on a daily basis. As a nurse, she treated her patients equally, and she gained the respect of her co-workers at the hospital.

Marthe Cnockaert: The Lady Double Agent of WWI
The town of Westrozebeke, Belgium still looks very similar to what it would have looked like back in World War I. Credit:

In 1915, a family friend named Lucelle Deldonck came to visit the Cnockaerts, and she asked Marthe if she wanted to serve her country by becoming a spy for British Intelligence. She agreed, and a few days later, an elderly woman who was selling beans in town slipped Marthe a piece of paper with instructions to meet a spy named “Lissette”, which she later learned was her family friend Lucelle’s spy name.

Marthe’s job was simple, but crucial. She was to continue living her day-to-day life, but keep her eyes and ears peeled for any information she may overhear from the German soldiers about locations of their ammunition, or plans of what they were going to do for the next attack. If she heard anything, she was supposed to meet up with members of the spy network, and get that information back to British Intelligence. A man with two safety pins on his collar was the person she knew to give her notes to. He knocked on her window in the middle of the night, and she would slip a piece of paper with encoded messages to him. This was not always the same man every night, but Marthe knew that as long as she saw the safety pins and knocked their secret knocks, she could trust him.

Marthe Cnockaert: The Lady Double Agent of WWI
In 1933, there was a movie based on MartheCnockaert‘s life, called “I Was a Spy”. The movie poster shows her passing secret messages to her fellow spies. Credit:

Marthe’s father bought a cafe in a nearby town called Rousseliere, which had apartments above it, so he could generate income, and give his family a new place to stay. German soldiers loved to go there to relax, and a few of the high-ranking members of the military were renting the upstairs apartments, as well. This was a perfect opportunity to eavesdrop on more German conversations, so Marthe would work there to help her father whenever she had a break from her shifts at the hospital. She got to know some of the German soldiers as friends, especially if she had been their nurse at one point. From the perspective of the Germans, she was being perfectly pleasant young woman, and she showed now signs that she resented them for burning down her house and occupying her country. Her family received letters from her brothers, so they knew that they were still alive, but that never takes away from the ongoing fear that they could die on the battlefield.

Marthe Becomes a Double-Agent

Marthe Cnockaert: The Lady Double Agent of WWI
The Iron Cross was the most prestigious award that anyone could earn in Germany. Credit:

At the hospital, Marthe Cnockaert would sometimes have to work 20 hours straight, because they were such a small town, and there were not enough trained nurses and doctors available. This meant that all of the German soldiers who were recovering from their wounds knew who she was, and really liked her. Two of the high-ranking Germans also saw her working as a waitress at her father’s new cafe. They noticed how devout she was to healing wounded men, so she was awarded with The Iron Cross, which is one of the highest German medals of honor. The ironic part was that one of these men, Otto von Prompt, was actually visiting Rousseliere to find and extract Belgian spies, but she managed to slip right under his nose.

During this time that she was making so many German soldier friends, Martha learned that over 1,000 enemy troops were staying inside of the brewery in Rousseliere. She was walking home at night, and mentally preparing what her note to the “safety pin man” should say. A strange man with two safety pins on his collar was approaching a house in front of Marthe, and she stayed back. She had never seen this man before, but that was to be expected, since new spies were being recruited all the time. But she had a strong feeling in the pit of her stomach to stand back.

She figured that it would be safer to wait in the shadows, as another woman slipped her own message to the fellow spy. After knocking on the window, the “safety pin man” pulled out a gun, and shot the woman who was passing the note.

Marthe Cnockaert: The Lady Double Agent of WWI
A movie based on Marthe’s autobiography was released in 1933, called I Was A Spy. Credit: YouTube

The Germans had infiltrated the spy ring. They knew about the safety pins, the secret knock, and the coded messages. Espionage was no longer safe, now that Otto von Prompt was out for blood. Since sending messages through the “safety pin man” was no longer safe, Marthe gave a note to her mother, who was able to smuggle the information across the border, and hand it off to her friend Lucelle. The message was given to the British Intelligence, and they prepared to bomb the brewery.

The next day, Otto Von Prompt grabbed Marthe by the arm while she was in her father’s cafe, and told her to come up to his apartment, because he wanted to speak privately. She was shaking, believing that she figured out she was part of the Belgian spy ring. To her surprise, he truly did think she was loyal to the Germans, so he asked her to become a spy for him, in order to wipe out the Belgian resistance.

Marthe agreed to think it over, because she had no choice but to become a double agent. That same night, bombs were dropped on the brewery where the German troops were sleeping. Marthe had to go to the hospital to treat the survivors, staying silent about the fact she was the spy who was responsible for the attack. Otto von Prompt was furious, so he urged Marthe to use her connections in town to figure out who had leaked the information. She didn’t want to falsely accuse someone else in the village, so she wrote up a piece of paper with random numbers and letters, claiming that it was some sort of secret code she found on the leg of a carrier pigeon. At first, Prompt was very happy to get this secret code and it distracted him for a short period of time, until he realized it was a total fake.

Marthe Cnockaert: The Lady Double Agent of WWI
Political cartoons during World War I depicting the massive hand of Germany destroying a Belgian village. Germany had an unfair advantage over a small country like Belgium. The atrocities that they committed against civilians was well publicized, and it motivated US and British soldiers to help. Credit: Wikimedia Commons.

The End of the Line

Marthe feared for her life. She knew it was only a matter of time before Prompt discovered that she was actually the spy who was responsible for the death of those men. Desperate for help, she found one of the safety pin men that she recognized in town, pulled them to the side, and told him exactly what was happening. The next day, Otto von Prompt was assassinated in his apartment.

Unfortunately, the relief was short-lived, because when the Germans conducted a search of her apartment above the cafe. They found some of her real coded messages, and arrested her. She fully expected to be executed that day, but instead, they kept her in jail for several weeks before being put on trial.

When she sat before the court of German officials, she told them that she saw herself as a Belgian soldier, and it was her duty to her country to do whatever she could to defend it against invaders. She did not incriminate herself unnecessarily, of course. If they knew the extent of the damage she had done to the German army, they truly would have killed her. She did not admit to leaking the information about the brewery, or her connection with the assassination to Otto von Prompt.

Marthe Cnockaert: The Lady Double Agent of WWI
Court scene from “I Was A Spy!” in 1933. Credit: YouTube

Instead of learning about her super-spy abilities, her friends at the hospital were there to testify for her character, including German doctors. They told the German judge how she spent the majority of her days and nights healing soldier’s wounds from both sides of the war, and that hundreds of men would have died without her. They also brought up the fact that she was awarded the Iron Cross for doing so. Based on the testimonies of the court, they must have thought she was harmless. She was found guilty of being a spy, which is normally a death sentence. However, since she had the Iron Cross, she was allowed to live in prison for the next two years, until the end of World War I.

When the war was over, she was released from prison, and the British, Belgian, and French government all gave her rewards for her work. She met a British officer named John McKenna, and they fell in love, and got married. She continued to live in Belgium, where she wrote her autobiography, called, I Was A Spy!


Where Do we get this Stuff? Here are our Sources.

Women Heroes of World War I: 16 Remarkable Resisters, Soldiers, Spies, and Medics. Kathryn Atwood. Chicago Review Press. 2014.