At the outbreak of the war in 1939, Zirnheld was assigned to a Défense Contre Avions (DCA) unit in Lebanon. Zirnheld tried to transfer to serve in the Metropolitan Army in France, but the Armistice was signed before he could do so. Zirnheld then defected to British-held Palestine to join the Free French forces. He was assigned to the 1st Colonial Infantry Battalion as a private and served at the Battle of Sidi Barani. Because of his education, he was reassigned as the Deputy Director of the Department of Information and Propaganda in Cairo. Although this was a "safe" position, he requested a frontline posting. He was then sent to the Officer Candidates' School in Brazzaville, French Congo, where he graduated 5th in his class as an Aspirant (Brevet-Lieutenant).