| Australian Army | |
|---|---|
 Members of the 7th Battalion in a trench at Lone Pine, 6 August 1915 | |
| Active | 1914–18 |
| Country | Australia |
| Allegiance | British Empire |
| Type | Army |
| Size | 416,809 (total) |
| Engagements | World War I |
The Australian Army was the largest service in the Australian military during World War I. The First Australian Imperial Force (AIF) was the Army's main expeditionary force and was formed from 15 August 1914 with an initial strength of 20,000 men, following Britain's declaration of war on Germany. Meanwhile, the separate, hastily raised 2,000-man Australian Naval and Military Expeditionary Force (AN&MEF), landed near Rabaul in German New Guinea on 11 September 1914 and obtained the surrender of the German garrison after ten days; it later provided occupation forces for the duration of the war. In addition, small military forces based on the pre-war Permanent Forces and part-time Citizen Forces were maintained in Australia to defend the country from attack.
The AIF initially consisted of one infantry division and one light horse brigade. The first contingent departed Australia by ship for Egypt on 1 November 1914, where it formed part of the Australian and New Zealand Army Corps (ANZAC). The infantry division fought during the Gallipoli Campaign between April and December 1915, 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, forming part of the I and II ANZAC Corps, which were committed to the fighting in France and Belgium along the Western Front in March 1916. Meanwhile, two mounted divisions remained in the Middle East to fight against Turkish forces in the Sinai and Palestine Campaign.
Later combined into the Australian Corps in 1917, the AIF divisions in France and Belgium were often used to spearhead operations, playing a significant role in the defeat of the German Army in 1918. By the end of the war the AIF had gained a reputation as a highly effective military force. Following the armistice on 11 November 1918, a process of demobilisation began, with the last Australian personnel being repatriated in late 1919. In all, 416,809 Australians enlisted during the war and 334,000 served overseas. The AIF sustained approximately 210,000 casualties, of which 61,519 were killed or died of wounds, a casualty rate among the highest of any belligerent for the war.