Upon the outbreak of the First World War Cros was recalled to metropolitan France and fought in defence of Paris at the First Battle of the Marne, leading an ad hoc unit of zouaves and tirailleurs. He was wounded and spent two days directing his troops from a horse-drawn carriage before he was forced to leave his command. On 15 September 1914 he was promoted to colonel and subsequently received command of the 2nd Moroccan Brigade which he led at the Battle of the Yser and the Second Battle of Artois. It was at Artois that he was killed in a German counter-attack. Cros' name is recorded alongside that of Colonel Pein, who commanded the 1st Moroccan Brigade at Artois, on the Moroccan Division Memorial at Vimy.