At the start of the German invasion of Belgium on 10 May 1940, Rajchmann went into hiding with a friend. After advising his wife who was staying at her parents house at 32 Avenue Jean Volders in Saint-Gilles to flee to France, Rajchmann took a train with his father-in-law and brother-in-law out of Belgium. His brother alighted at Tournai, while they both continued travelling to Montréjeau. When Rajchmann arrived in Montréjeau, he was interned at the Saint-Cyprien internment camp. His father, who was not arrested, went to stay in Revel in Haute-Garonne. The Saint-Cyprien internment camp was established on the 8 February 1939 at Saint-Cyprien coastal strip in Rosellón along with several other internment camps in the same location. Its main purpose was the hold Republican prisoners who were fleeing the Republican defeat at Barcelona on 26 January 1939. By March 1939, it held 90000 prisoners.