The 18th Battalion was an infantry battalion of the Australian Army. During World War I, the battalion was raised in 1915 as part of the Australian Imperial Force, attached to the 5th Brigade, of the 2nd Division. It was sent initially to Gallipoli, where it suffered many casualties before it was withdrawn from the line and sent to France and Belgium, where it served at the Western Front as part of the Australian Corps and took part in most of the major battles between 1916 and 1918. The battalion's last engagement of the war was at Montbrehain in October 1918 and it was disbanded in April 1919.

5th Brigade is a brigade of the Australian Army. Originally raised as a militia formation in 1912, the 5th Brigade was re-raised for overseas service in 1915 as part of the Australian Imperial Force during the First World War. The brigade then served during the Gallipoli Campaign and on the Western Front. During the inter-war years, it was re-raised as a part-time formation as part of Citizens Military Force. It undertook garrison duties in Australia during the Second World War, but was not deployed overseas before being disbanded in 1944. Following the war, the brigade was re-raised in 1948 once again and it is currently a Reserve combined arms formation based in New South Wales and forms part of the 2nd Division.