 The First Australian Imperial Force ( 1st AIF ) was the main expeditionary force of the Australian Army during World War I. It was formed on 15 August 1914 , following Britain 's declaration of war on Germany , initially with a strength of one infantry division and one light horse brigade . The infantry division subsequently fought at Gallipoli between April and December 1915 , being reinforced by a second division which was later raised , as well as three light horse brigades . After being evacuated to Egypt the AIF was expanded to five infantry divisions , which were committed to the fighting in France and Belgium along the Western Front in March 1916 . A sixth infantry division was partially raised in 1917 in the United Kingdom , but was broken up and used as reinforcements following heavy casualties on the Western Front . Meanwhile , two mounted divisions remained in the Middle East to fight against Turkish forces in the Sinai and Palestine . 
