The outbreak of war was greeted in Australia, as in many other places, with great public enthusiasm.
In response to the overwhelming number of volunteers, the authorities set exacting physical standards for recruits.
Yet, most of the men accepted into the army in August 1914 were sent first to Egypt, not Europe, to meet the threat which a new belligerent, the Ottoman Empire (Turkey), posed to British interests in the Middle East and the Suez Canal.
An Australian digger uses a periscope in a trench captured during the attack on Lone Pine, Gallipoli, 8 August 1915.
After four and a half months of training near Cairo, the Australians departed by ship for the Gallipoli peninsula, with troops from New Zealand, Britain, and France.
The Australians landed at what became known as ANZAC Cove on 25 April 1915 and established a tenuous foothold on the steep slopes above the beach.
During the early days of the campaign, the allies tried to break through Turkish lines, while the Turks tried to drive the allied troops off the peninsula.
Attempts on both sides ended in failure and the ensuing stalemate continued for the remainder of 1915.
The most successful operation of the campaign was the evacuation of troops on 19 and 20 December, under cover of a comprehensive deception operation.
As a result, the Turks were unable to inflict more than a very few casualties on the retreating forces.
After Gallipoli the AIF was reorganised and expanded from two to five infantry divisions, all of which were progressively transferred to France, beginning in March 1916.
The AIF mounted division that had served as additional infantry during the campaign remained in the Middle East.
When the other AIF divisions arrived in France, the war on the Western Front had long been settled in a stalemate, with the opposing armies facing each other from trench systems that extended across Belgium and north-east France, from the English Channel to the Swiss border.
The development of machine-guns and artillery favoured defence over attack and compounded the impasse, which lasted until the final months of the war.
Troops of 53rd Battalion wait to don equipment for the attack at Fromelles, 19 July 1916. Only three of these men survived.