These efforts took on pressing importance when, after their conquest of Poland, the Nazis turned their armies toward France. At that time, the French government issued a call for every able-bodied man to register for army service. The Rebbe reported to the draft office and was given a certificate attesting to his willingness to serve. Although he was never summoned for military duty, this certificate proved very useful. For he was frequently stopped in the street and asked to prove his identity and to show that he was not a draft-evader.

When the Nazis entered Paris, they immediately ordered a census of all the inhabitants, including information regarding their race and religion. When they came to the Rebbe's apartment, he was not home. Since their intent was obvious, when asked regarding their religion, one of the people staying in the apartment answered, "Orthodox." This was not a lie, because it could have been interpreted as "Orthodox Jews." Nevertheless, the implication was "Russian Orthodox ." When the Rebbe returned and heard of this, he hurried to the census office and asked to correct the matter by adding the word "Jew."

The Rebbe sought to leave Paris where the Nazis had vigorously imposed their rule. One of his acquaintances, a general in the French army, offered to let him stay in a castle outside the city's suburbs. The Rebbe, however, declined the proposal, explaining that the Nazis' rule over Paris would be longer and more difficult than people conceived. Instead, he and the Rebbitzin fled to Vichy, which was still under French control, departing on the last train to leave Paris.

They arrived shortly before sunset on the day before Shavuos. Unable to reach their hotel before the holiday, the Rebbe sent their belongings with a taxi and he and the Rebbitzin made their way by foot, a journey of several hours.

They stayed in Vichy only for a few months. Afterwards, the Rebbe chose to continue to Nice which was under Italian rule. Although allies of the Nazis, the Italians showed more understanding toward the Jews and many were able to live there in relative security.