He became acting commanding officer of his battalion in February 1917 and led his regiment at the Second Battle of Kut in February 1917 and the Fall of Baghdad in March 1917. Having been mentioned in despatches and having received the Distinguished Service Order in 1917 for his service in Mesopotamia, he was promoted to the substantive rank of major on 21 January 1918, to temporary lieutenant-colonel on 23 May 1919 and to brevet lieutenant-colonel on 15 November 1919 for his "distinguished service in Southern and Central Kurdistan" on the recommendation of the Commander-in-Chief of the Mesopotamia Expeditionary Force.