Before 1914, Australia only had a ground forces for home defence. A little regular army was formed in 1901 and they  were also a part-time volunteer militia (45,000 men in 1914). Men of combat age have to undertake minimal military training regularly. On 3 August 1914, the Australian government offered Great Britain 20,000 men for the war effort. Consequently, a new volunteer force for overseas service was created: the AIF (Australian Imperial Forces).

That army benefitted of an intensive recruitment campaign and a popular enthusiasm for War. The first AIF and New Zealand troopships left Western Australia on 7 November 1914 and a second convoy sailed on 31 December. Recruitment decreased from 1915, but conscription was always refused except by extreme British nationalists. A total population of about five millions eventually contributed about 322,000 volunteers. Among them, 280,000 were casualties (including almost 60,000 dead), one of the highest rate of attrition suffered by a national army.

Overseas forces were composed of five Australians divisions. With New Zealand Forces and some British units, they formed the Australian and New Zealand Army Corps (ANZAC) until late 1917. After there was only a single Australian Corps. ANZAC or diggers  - their knickname after Somme battle -used to lack of military etiquette what many British officers could not accept. However, by 1918 Australians were generally recognized as one of the best fighting troops.

Australian units were sent first to Egypt for training, some participated in the defense of Suez. The first big involvement was Gallipoli in 1915, where they proved their military value. AIF arrived in France in 1916 where it took part at a series of campaigns on the Western Front still 1918. Under Australian general John Monash from may 1918, Australians led Allied counteroffensives in the central sector of the front from Hamel until just before the Armistice. Australian Cavalry Brigades first fought dismounted in Gallipoli and France and were then transferred to Palestine in 1917-1918 and played a vital role in Allenby’s victories.