The 15th Battalion was an infantry battalion of the Australian Army. Formed in 1914 as part of the all-volunteer Australian Imperial Force from Queensland and Tasmanian recruits, the battalion fought during the Gallipoli Campaign and on the Western Front during the First World War. It was disbanded after the war in 1919, but later re-raised as a part-time Citizens Forces unit based in Queensland in 1921, consisting of a mixture of volunteers and conscripts. Economic pressures and limited manpower resulted in the battalion being amalgamated with other battalions a couple of times during the inter-war years. In mid-1939, as rising tensions in Europe led to an expansion of the Australian military, the battalion was re-formed in its own right. During the Second World War the 15th Battalion was mobilised for wartime service and initially undertook defensive duties in Australia before taking part in the fighting against the Japanese in New Guinea and Bougainville in 1943–1945. The battalion was disbanded in 1946 and never re-raised.

The 4th Brigade is a brigade-level formation of the Australian Army. Originally formed in 1912 as a Militia formation, the brigade was re-raised for service during World War I, elements of the brigade served at Gallipoli and in the trenches on the Western Front before being disbanded in 1919. In 1921, the brigade was re-raised as a unit of Australia's part-time military forces, based in the state of Victoria. During World War II the brigade served in the New Guinea and New Britain campaigns. Following the war, the brigade formed part of the 3rd Division, however, it was later reallocated to the 2nd Division, where it serves as a Reserve combined-arms formation including units and personnel from all corps of the Army including armoured, infantry, artillery, engineers, signals and ordnance.