The 20th Battalion was an infantry battalion of the Australian Army. Raised in early 1915 as part of the Australian Imperial Force, it was attached to the 5th Brigade, 2nd Division that served during World War I. The battalion first saw action during the Gallipoli campaign, before being evacuated in December 1915. After that the 20th Battalion was sent to France where they served in the trenches along the Western Front. Over the course of the next two years, they fought in many major battles, including the battles of the Hundred Days Offensive at the end of the war. The 20th Battalion's last engagement was at Montbrehain in October 1918. Following the end of the war, it was disbanded in April 1919. It was later re-raised in 1921, although it was amalgamated in 1929 due to manpower shortages. During World War II the battalion was briefly re-raised and carried out garrison duties in Australia.

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.