Alexander returned to the Western Front in August 1915, fought at the Battle of Loos and was, for ten days in October 1915, an acting major and acting Commanding Officer (CO) of the 1st Battalion, Irish Guards as a "Battle Casualty Replacement".
On 10 December 1916, his twenty-fifth birthday, Alexander became second-in-command (2-i-c) of the 1st Battalion, Irish Guards as an acting major [REF].