The First Australian Imperial Force (1st AIF) was the main expeditionary force of the Australian Army during World War I. It was formed from 15 August 1914, following Britain's declaration of war on Germany. Generally known at the time as the AIF, it is today referred to as the 1st AIF to distinguish from the 2nd AIF which was raised during World War II. The 1st AIF included the Australian Flying Corps, which was later renamed the Royal Australian Air Force.
The 1st AIF was a purely volunteer force for the duration of the war. In Australia, two plebiscites on conscription were defeated, thereby preserving the volunteer status but stretching the AIF's reserves towards the end of the war. A total of 331,814 Australians were sent overseas to serve as part of the AIF, which represented 13% of the white male population. Of these, 18% (61,859) were killed. The casualty rate (killed or wounded) was 64%. About 2,100 women served with the 1st AIF, mainly as nurses. Close to 20% of those who served in the 1st AIF had been born in the United Kingdom but all enlistments had to occur in Australia (there were a few exceptions). As a volunteer force, all units were demobilized at the end of the war.