Early in World War II, from May to June 1940, he was the youngest French general. He led his division during the Battle of France, at the battles of Rethel, Champagne-Ardenne, and Loire and until the Armistice of 22 June 1940. During the Vichy Regime, he remained in the Armistice Army, first in regional command posts, then as commander-in-chief of troops in Tunisia. After the disembarking of Allied forces in North Africa, on 11 November 1942, the Germans invaded the free zone; de Lattre, Commander of the 16th Military Division at Montpellier, refused the orders not to fight the Germans and was the only active general to order his troops to oppose the invaders. He was arrested but escaped and defected to Charles de Gaulle's Free France at the end of 1943. From 1943 to 1945 he was one of the senior leaders of the Liberation Army, commanding the forces which landed in the South of France on 15 August 1944, then fought up to the Rivers Rhine and Danube. He was the only French general of World War II to command large numbers of American troops, when the US XXI Corps was attached to his First Army during the battle of the Colmar Pocket. He was also the French representative at Berlin on 8 May 1945, with Eisenhower, Zhukov and Montgomery.