at a registry office in Collingwood. The ceremony was kept secret, because at the time junior officers required the Army's permission to marry, and at age 20 Robertson would not have received it. Later they would claim that they had been married in 1916. Their marriage produced no children. First World War Major General William Bridges decided that the Duntroon cadets, none of whom had yet finished their training, should be split up and posted to the various units of the AIF as regimental rather than staff officers. Robertson was posted to the 10th Light Horse as its machine-gun officer. He was one of seven members of his class in the 3rd Light Horse Brigade. By the end of August 1915, three of them would be dead. 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. The 10th Light Horse was reorganised after returning to Egypt in January 1916, and Robertson assumed command of B Squadron, with the AIF rank of major from May 1916. This was as far as he could go, for Duntroon graduates could not be promoted above major in the AIF. This was the result of an AIF policy aimed at giving them a broad a range of experience, which would benefit the post-war Army, while not allowing an accumulation of young officers of high rank, for whom the reduced post-War Army would not have sufficient posts. His substantive rank remained that of lieutenant; he would not be promoted to the substantive rank of captain in the PMF until 30 September 1920, and promotion to major would not come until 1 July 1932. At the Battle