On the outbreak of the Second World War, Prince Louis wrote to the French prime minister, Édouard Daladier, offering to serve in the French Army. His offer was refused, and so he assumed the "nom de guerre" of "Louis Blanchard" and joined the French Foreign Legion, seeing action in North Africa before being demobilised in 1941, following the Second Armistice at Compiègne. He then joined the French Resistance and was arrested by the Germans after attempting to cross the Pyrenees on his way to London to join Free French leader Charles de Gaulle. Following his arrest, he spent time in various prisons, including Fresnes. Following his release, he joined the French Resistance group "Organisation de Résistance dans l'Armee" under the name "Louis Monnier". Another member of the Charles Martel Brigade to which he belonged was his cousin Joachim, Prince Murat, who was killed in July 1944. Prince Louis himself narrowly escaped death a month later when, on 28 August, he was badly wounded as part of a seven-man patrol that came under attack; he was the sole survivor. Following his recovery, he joined the Alpine Division and was later decorated for bravery.