Dalziel volunteered for the Australian Imperial Force (AIF) in early 1915 and was posted to the 15th Battalion as a reinforcement. He served throughout the Gallipoli Campaign until he was evacuated, along with the rest of his battalion, to Egypt in December 1915. From July 1916, he served on the Western Front in France and fought in the Battles of the Somme, Pozières and Mouquet Farm. His service continued into 1917, including the Battle of Messines but he was wounded during the Battle of Passchendaele at Polygon Wood. He returned to the front in June 1918.