In July 1937, Besson was promoted to full general, commanding the Sixth Army, and he became a member of France's Supreme War Council. During the German invasion of France in May and June 1940, he commanded the 3rd Army Group (consisting of 3 armies totaling 36 divisions on the extreme right flank of the Allied line) on the Colmar-Mulhouse section of the front, protected by the Jura Mountains and Switzerland. During the German assault, Besson's troops found the overwhelming German air superiority particular demoralizing.
Following the German breakthrough, Besson followed orders and withdrew to the Seine River on 8 June, to positions below the Aisne and the Somme Rivers as far as Neufchâtel. Within a week, as his men retreated in disorder to be isolated on the Loire River, he had become a strong advocate of signing an armistice, preferring that outcome to the continued and senseless slaughter of his forces. Besson spent the remainder of the war as a German prisoner of war, sparing him the opprobrium attached to many Vichy officials. Subsequently, he became director of the French Prisoner of War Service. He died in Paris on 25 July 1969. Priscilla Roberts
Crémieux-Brilhac, Jean-Louis. Les Français de l'an 40. 2 vols. Paris: Gallimard, 1990.; Draper, Theodore. The Six Weeks' War: France, May 10–June 25, 1940. New York: Viking, 1964.; Horne, Alistair. To Lose a Battle: France 1940. Boston: Little, Brown, 1969.; Spears, Edward L. Assignment to Catastrophe. 2 vols. New York: Wynn, 1954–1955.