The 21st Brigade was formed on 4 April 1940 and was composed of the 2/14th Battalion from Victoria, the 2/16th from Western Australia, and the 2/27th from South Australia. It was intended that along with the 19th and 20th Brigades it would form the 7th Australian Division. By the time the 7th Division was deployed operationally for the first time in April 1941, however, the 21st was the only original brigade that remained on its order of battle. Its sister formations were now the 18th and 25th Brigades, and would remain so for the rest of the war. The 21st Brigade's major campaigns were the invasion of Syria and Lebanon June-July 1941); the withdrawal on the Kokoda Trail (August-September 1942) and the destruction of the Japanese beachheads in Papua (December 1942-January 1941); the capture of Lae (September 1943) and the Ramu Valley-Finsterre Mountains advance (September 1943-February 1944) in New Guinea; and the Balikpapan landing in Dutch Borneo (July-August 1945). The 21st Brigade disbanded in 1946.