In 1942 Degueldre clandestinely entered the occupied zone to join the French Resistance under Roger Pannequin and engaged the 10th German Motorized Infantry Division at Colmar in January 1945. He then joined French Foreign Legion, under the name of Roger “Legueldre” with a claimed birth on 18 September 18, 1925 in Gruyeres in Switzerland. As a foreigner he would be eligible to join the Foreign Legion. His identity was formally corrected in 1955. He reached the rank of warrant officer in Indo-China and was received the Croix de Guerre des Théâtres d'Opérations Extérieures. After the battle of Điện Biên Phủ, he transferred to the 1st Foreign Parachute Regiment and was assigned to the Algerian conflict. He was made an officer and a knight of Légion d'honneur (Legion of Honour).