The 10th Light Horse was concentrated at Claremont, Western Australia, before departing for the Middle East on the transport "Mashobra" in February 1915. After arriving at Alexandria, Egypt, in March 1915, the regiment moved to Mena Camp near Cairo. In May, the 3rd Light Horse Brigade began moving, without horses, to Gallipoli, preceded by the machine-gun sections, which embarked at Alexandria on 8 May 1915. At Gallipoli, the machine guns were brigaded together to provide additional firepower. Robertson's machine guns were in support during the disastrous Battle of the Nek on 7 August 1915, during which much of the 10th Light Horse became casualties. Afterwards, Robertson was promoted to captain and became second in command of A Squadron. He assumed command of C Squadron on 28 August, and led it in the fighting at Hill 60 the next day.