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 shortage