Born on 28 October 1892, in Westrozebeke, a remote village in the Belgian province of West Flanders, Marthe Mathilde Cnockaert was one of five children of Félix and Marie-Louise Cnockaert, who were farmers before the war. She was studying at the medical school at Ghent University, but her studies were interrupted by the outbreak of the World War I.In the month of August 1914, German troops invaded their peaceful village, killed about a thousand villagers and burned it down completely. While she was able to escape with her parents, they were left homeless.
As they took shelter in the house of a kind neighbour, Marthe’s father decided to move to the nearby Rousseliere town, with the hope to find a way to earn money and find a place of living. Meanwhile, her brothers had already left to serve the country in the Great War, only Marthe stayed behind in Westrozebeke with her mother. Armed with her medical knowledge, Marthe became successful to get a job of a nurse at the local hospital and started to treat both Belgian and German soldiers on a daily basis and was valued for her medical training and her multi-lingual skills, speaking English and German as well as French and Flemish.Within a short time, she gained the respect of her colleagues for her efficiency and sincerity.
In 1915, she was transferred to the German Military Hospital in Roulers, where she shifted with her parents. Around that time, she was approached by a family friend and former neighbour, Lucelle Deldonck, who asked her, if she is interested to serve her country as a spy, attached to an Anglo-Belgian intelligence network operating in the town and she agreed. Her job was simple, while she was to continue her daily life as before as a dedicated nurse, she was to keep her eyes and ears alert to gather any information that she may gather by overhearing the conversation of the German soldiers, about the locations of their ammunition or their plans for any future attack. She was to relay the information to other agents attached to the spy network, for their onward passing that information to the British Intelligence. Most of the time, her contacts were two other female Belgian spies, an elderly vegetable seller code-named ‘Canteen Ma’, and a letter-box agent code-named ‘Number 63’.
Meanwhile, Marthe’s father bought a cafe in Rousseliere, which had apartments on the upstairs. The German soldiers loved to visit the cafe to relax and apart from that, some of the high-ranking members of the military also took rent of the upstairs apartments. Marthe strongly felt, the place would provide her a perfect opportunity to eavesdrop on more German conversations. To grab the opportunity, she started to help her father by working as a waitress in the café, whenever she had a break from her shifts at the hospital. As a result, she became friendly with some of the Germans, especially if she had been their nurse at one point.
Thus, for two years, Marthe Cnockaert secretly carried her code-named ‘Laura’, used her cover as a nurse at the hospital and as a waitress at her parents' café, to gather important military intelligence for the benefit of the British and their allies. Apart from Canteen Ma and Number 63, she came to know that, any man with two safety pins on his collar was the person to whom she should hand over her notes. She would slip a piece of paper with encoded messages to the unknown hand, which knock on her window in the middle of the night. She used to pass coded messages about the movements of German troops and also helped the Allied prisoners to escape when they were brought to the hospital.During the war, she was instrumental in destroying a telephone line which a local priest was using to spy for the Germans. She also gathered details of a planned but cancelled visit by Kaiser Wilhelm II, for a British aerial attack.
As the small town hospital did not have sufficient trained nurses and doctors, Marthe Cnockaert had to work hard and sometimes had long working hours, which continued for about 20 hours at a stretch. As a result, all the ailing German soldiers knew her by name and by face and liked her dedication. Apart from that, two high-graded Germans also noticed her working sincerely as a waitress at her father’s new cafe. The appreciation of all these people helped her in achieving the Iron Cross, one of the highest German medals of honour. One of those influential persons, who appreciated her dedication, was Otto von Prompt, who was actually visiting Rousseliere to find the Belgian spies.
In the meantime, Marthe came to know that over 1,000 German troops were sheltered inside of the brewery in Rousseliere. However, she also knew that sending the message through a man with ‘safety pin’ is not at all safe, since by that time, the Germans became aware about the so called safety pins, the secret knocks on the window in the wee hours of the night and the coded messages. She, therefore, gave her message to her mother, who smuggled the information across the border, to reach it safely to her contact Lucelle.
On the next day, when Otto Von Prompt grabbed Marthe by the arm in her father’s café and asked her to meet him upstairs, in his apartment, for an important private talk, Marthe was almost sure that her game was over. However, to her utter surprise, Otto told her that he trust Marthe as loyal to the Germans and asked her to work as a German spy to help him to wipe out the Belgian resistance. Marthe had to agree to think it over, as she had no other choice but to become a double agent. During the same night, bombs were dropped on the brewery where the German troops were sleeping. Nevertheless, Marthe was scared of her life. She knew that she would be caught by Otto at any moment. Desperate to save her life, one day as she came across one of the safety pin men on the road, she pulled him to the side and told him everything in short. It yielded a quick result, as Otto von Prompt was assassinated in his apartment on the next day.
In the autumn of 1916, Marthe discovered an abandoned sewer tunnel that ran beneath the German ammunition depot. As she dispatched the news, she was ordered to blow it up. Accordingly, Marthe and another agent named Alphonse, placed dynamites at just the right spot to destroy the depot. Unfortunately, during the operation, Marthe lost her watch, engraved with her initials and the Germans discovered it. Naturally, the Germans became suspicious about Marthe, searched her home, found hidden coded messages and arrested her on espionage charges. During interrogation, she refused to betray her comrades and was sentenced to death for her espionage. However, in spite of learning about her super-spy abilities, her colleagues at the hospital, including the German doctors vouched for her character. Her clean record, her dedicated and impartial service as a nurse and above all, the award of the Iron Cross, saved her life. Her death sentence was commuted to life and she served only two years in a prison in Ghent, as she was released after the end of the Great War in 1918.
After her release, Marthe Cnockaert received honours from France and Belgium and was hailed by Field Marshal Sir Douglas Haig of Britain in his dispatches on 8 November 1918. In addition, she received a British certificate for gallantry from Winston Churchill, who led Britain to victory in the Second World War. Later, she met and married John McKenna, a British Army Officer and moved to England. Her memoir, I Was a Spy, published in 1932, received rave reviews and initially sold around 200,000 copies. It was adapted into a successful movie of the same title in 1933. After that, Marthe and her husband published more than a dozen spy novels. Though the books were published under Marthe’s name, it is maintained by many that the books were actually written by John McKenna.
The couple moved back to Marthe's family home in Westrozebeke around 1947. John McKenna left Marthe for another woman sometime in the early 1950s. They did not have any issue and Marthe McKenna lived largely in isolation, until her death around 1966.