Guy de Montlaur was at the front at the onset of the war on 3 September 1939. He was with the based at Sarreguemines, regrouped in the and took part from the start of the war in numerous raids in Saarland, Germany (Kleinblittersdorff, Walsheim, Herbitzheim and German Bliesbruck). His unit became part of the from 17 October, he was under the command of Capitaine de , future commander at Dien Bien Phu in 1954. In June 1940, Montlaur was fighting the invasion in a losing battle and ended in Limoges two days after the armistice was conceded by Pétain to Hitler. In 1942, after crossing Franco's Spain, he arrived in Lisbon, where for three months he worked for MI6.