Codenamed Amniarix, she evaded Gestapo agents while gathering crucial information on the Germans' emerging rocket weapons programs from behind enemy lines.

Her intelligence reports, forwarded to London, led directly to the British raid on Peenemünde and to delays and disruptions in the V-1 and V-2 programs, saving many thousands of lives in the West.

After the outbreak of World War II, she moved with her family to Dinard, in Ille-et-Vilaine, where the mayor, a friend of her parents, asked her to work as an interpreter to facilitate negotiations between the local services and the German authorities.

She took a job at the French national chamber of commerce as a translator and soon became the organization's top staffer, meeting regularly with the German military commander's staff.

She was a frequent visitor with the Germans, discussing commercial issues, such as complaints about Nazi commandeering or offers to sell them goods, such as steel and rubber.

In 1941 she moved to Paris where she began working for a Parisian company that supplied materials to the German war effort, thus positioning herself as a source of valuable information for the Allied forces.

[8] Lamarque remembered Rousseau from the University of Paris, where she had shown talent in languages, including German, and finished first in her class, in 1939.

Her collection and forwarding of this intelligence under very difficult circumstances led, through Jones' analysis and persuasive abilities in London, to British air raids on Peenemünde.

While recovering in Sweden from tuberculosis contracted during her imprisonment, Rousseau met Henri de Clarens, who had been in the Buchenwald and Auschwitz concentration camps.