[1] After the installation of the Vichy regime, Bloch was barred from her laboratory because she was a Jewish communist and had to work as a tutor in order to survive.

In 1941, she participated in the first groups of the communist resistance led by Raymond Losserand and installed a small, rudimentary laboratory in her two-room apartment on the Place du Danube located in the 19th arrondissement in Paris.

Taking the name Claudia in hiding, she worked with Colonel Dumont making grenades and detonators used in attacks organized by the youth resistance (called the Young Battalions) at the end of August 1941.

After four months of interrogation and torture, she was condemned to death by a German military tribunal, along with 18 co-conspirators (who were all immediately executed).

On the site of the Hamburg prison, a plaque on the back wall of the detention center commemorates two members of the Resistance who were killed there.

[3]Bloch's husband, Frédo Sérazin was arrested in February 1940, under the Daladier government, imprisoned first at the Sisteron fortress in March 1940, then at Châteaubriant, and finally at the Voves camp.