During the early stages of World War I, "Sydney" was involved in supporting the Australian Naval and Military Expeditionary Force, and escorting the first ANZAC convoy. On 9 November 1914, she defeated the German cruiser at the Battle of Cocos. During 1915 and 1916, "Sydney" operated on the North America and West Indies Station, before joining the 2nd Light Cruiser Squadron at Greenock, Scotland in November 1916. On 4 May 1917, the cruiser was involved in an inconclusive action against the German zeppelin "L43"; neither was damaged. During late 1917, "Sydney" became the first Australian warship to launch an aircraft, and the first warship to do so from a rotatable platform.