In November 1942, after the German Army moved into unoccupied France and took it over to counter the threat from the Allies, who had just landed in North Africa, the French government at Vichy transferred Mandel and Reynaud to the Gestapo upon their request. The Gestapo deported Mandel to KZ Oranienburg, and then to KZ Buchenwald, where he was held with the French politician Léon Blum.