Ecole Spéciale Militaire as a lecturer in musketry on 18 October 1890. Diou left St-Cyr on 11 October 1894 when he rejoined the 69th Infantry Regiment, assuming responsibility for their musketry and training. In early 1895 he received command of a company before, on 29 December 1895, he was promoted to chef de bataillon in the 4th Regiment of the Algerian Tirailleurs with the Army of Africa. He served with them in Tunisia from 6 February 1896 and was appointed a chevalier of the Legion of Honour on 29 December. Transferred to command the 4th Battalion of the Light Infantry of Africa on 29 December 1897, Diou received praise for his service at Gabès which was acknowledged as a difficult posting. He remained in Tunisia until November 1900 and received the Colonial Medal for his service there. Diou served in the French possession of Tonkin, Indo-China in 1900–1 and also apparently saw action in the Boxer Rebellion, receiving the 1901 China expedition commemorative medal. He returned to Tunisia on 21 October 1901, was appointed an officer of the Tunisian Order of Glory on 14 June 1903 and was promoted to lieutenant-colonel of the 121st Infantry Regiment on 31 December. Diou was appointed a commander of the Order of Glory on 3 May 1904. He transferred to the 2nd Regiment of Algerian Tirailleurs on 21 May 1906 and served in Algeria and the wider Sahara region until 29 August 1907. Diou was posted to Morocco on 30 August 1907, transferred to the 56th Infantry Regiment on 21 January 1908 and was promoted to colonel of the 81st Infantry Regiment on 23 February 1908. He was engaged in the action at Taddert on 11 July 1907 and at the affair at Sidi Bahin on 25 July 1907. Diou saw action in the landings at Casablanca in 1908 that led to the establishment of the French protectorate of Morocco and commanded the French column operating upon the Moroccan coast thereafter. He fought eight battles in Morocco in early 1908 and was mentioned in dispatches at the army level for actions against the enemy at Oued Aceila on 8 March 1908. The French commander in Morocco, General Albert d'Amade, praised Diou's actions there stating that he "took part in almost all the engagements of the historic campaign in Casablanca and the outlying regions" and that he was sure to set an "example of calm