Upon establishment, the men from the 7th ALH formed the bulk of Regimental Headquarters, and A and B Squadrons, while AIF volunteers made up the remainder of the new unit. Among them were veterans of the New South Wales Lancers who had fought in South Africa. Sailing from Sydney on 19 October, the 1st Light Horse disembarked in Egypt on 8 December 1914 and later went on to fight in Gallipoli, after being dispatched there in May 1915 with the 1st Light Horse Brigade. Serving in a dismounted role, they reinforced the New Zealand and Australian Division around Anzac Cove, and undertook mainly defensive tasks. In August, the regiment mounted a diversionary assault around a position dubbed "the Chessboard", where they suffered heavy casualties. After withdrawal from Gallipoli in December 1915, the regiment returned to a mounted role and was assigned to the Anzac Mounted Division. After defensive duties around the Suez Canal, the regiment joined the Sinai and Palestine campaign against Turkish forces. Its first battle came at Romani. It was followed by numerous others over the next two-and-a-half years, including Maghdaba, Rafa, Gaza, Jaffa, Es Salt, before the war end in late 1918.