Before the Federation of Australia, each of the six self-governing colonies had individual armies consisting of full-time soldiers, militia and volunteer units. In March 1901, the Commonwealth government assumed control of defence matters, merging the colonial forces to form the Commonwealth Military Forces (CMF).
Previously, the colonial forces had participated in fighting in New Zealand in the Anglo-Maori wars, in China in the Boxer Rebellion, South Africa in the Boer War, as well as rebellions within Australia.
The process of unifying the armies was undertaken while forces were still active in South Africa, with 28,923 soldiers now falling under the banner of the new Australian Army.
Former commander of the NSW military contingent, Major General Sir Edward Hutton, became the first commander of the CMF later in 1901, returning to Australia after a five-year hiatus after serving in Ireland, South Africa and the United Kingdom.
Sir Edward was tasked with structuring the new army, and oversaw the introduction of the Defence Act of 1903, which brought all the military units under a unified legislation, as well as empowering the Commonwealth government to be able to call up 'unexempted' males in times of war for home defence.
However, these forces could not be used in industrial disputes and couldn't serve outside of Australia, but led to the Defence Act of 1909, which saw the introduction of the country's first universal training scheme, which required males between 18 and 60 years to perform militia service within Australia and its territories.
This training scheme came into operation in 1911 and saw the establishment of the Royal Military College in Duntroon as well as a system of universal national service.
Males aged 12-18 became cadets, and men aged 18-26 were forced to serve in the CMF, however, when World War I broke out just three years later, a new force was required to be established due to the Defence Act of 1903 forbidding the CMF from fulfilling Australia's pledge to supply 20,000 men to support the British Forces.
World War I
Hence, the Australian Imperial Force (AIF) was formed in August 1914, consisting of an all-volunteer force, with men stumbling over themselves to enlist, in a conflict that was expected to be over by Christmas.
Eventually, over 400,000 would enlist to serve in the first AIF.
Australia's first significant involvement in the Great War was the Australian Naval and Military Expeditionary Force's (ANMEF) landing on Rabaul on 11 September 1914, and then taking possession of German New Guinea at Toma less than a week later, followed by the neighbouring islands of the Bismarck Archipelago in October.
Six months later, nearly 104 years ago to the day, members of the AIF landed on Gallipoli in Turkey with troops from New Zealand, forming the Australian and New Zealand Army Corps (Anzac).
This began the most well-known and revered involvement of the Australian Army in conflict, in a hellish situation in a picturesque setting, as the Anzacs attempted to establish a foothold on the Gallipoli peninsula.
Over 2,000 of the 16,000 Anzacs were injured or killed on the first day of the invasion.
Overall, the operation resulted in 26,111 Australian casualties, including 8,141 deaths.
Attempts from both sides, the Anzacs trying to advance and the Turkish lines seeking to push them back, ended in a stalemate that lasted the rest of 1915, and resulted in the daring evacuation of troops.
Despite being a military failure, with the battle at Gallipoli said to have "no influence" on the course of the war, the Anzac legend was born, with the characteristics of bravery, ingenuity, endurance and mateship coming to be important and defining characteristics of the Australian personality.
Nearly two decades after, Mustafa Kemal Ataturk, regarded as the "saviour" of the Turks at Gallipoli and a father figure of the country formed after the first world war, wrote a tribute to the Anzacs, saying, "Those heroes who shed their blood and lost their lives… you are now lying in the soil of a friendly country. Therefore rest in peace.
"There is no difference between the Johnnies and the Mehmets to us where they lie side by side here in this country of ours. You, the mothers who sent their sons from far away countries, wipe away your tears. Your sons are now lying in our bosom and are in peace. After having lost their lives on this land, they have become our sons as well."
Following Gallipoli, AIF forces fought in campaigns on the Western Front and Middle East, which resulted in heavy losses and few victories.
On the Western Front, Australia played a vital role in a series of advances in 1918, before being relieved in October, with Germany surrendering a month later.
In the Middle East, the AIF was involved in the defence of the Suez Canal as well as the re-conquest of the Sinai Desert, culminating in the occupation of Lebanon and Syria and eventually the suing of peace by Turkey in late October.
The first World War was the costliest conflict for Australia in terms of deaths and casualties, with over 60,000 killed and 156,000 wounded, or taken prisoner, from the 416,809 men that enlisted.
The AIF was officially disbanded in 1921, with focus returning to boosting Australia's CMF forces, which formed the expectation of a force of around 270,000 to be able to be assembled at short notice to defend Australia.
World War II
However, when the Second World War broke out, and once again to comply with the laws forbidding overseas service from the local militia, the second AIF was formed to allow volunteers to support Australia's commitment to support the British.
The first two years of Australia's involvement in WWII was in Europe, the Middle East and North Africa, however when Japan entered the war in 1941, Australian attention shifted from British needs, and focused on needs for themselves.
Britain had made it clear that it may be unable to help defend the countries on Australia's doorstep, and with the fall of Malaya and Singapore, the threat of a Japanese invasion became very real.
Due to the time it would take to withdraw AIF forces from other side of the world, the majority of forces available to defend Australia came from the CMF militia, which was a force of around 265,000 men at this point.
Volunteers from the militia were integral to the Pacific War. After beginning as garrison troops, they soon found themselves defending vital strategic passages on Australia's doorstep, including the Kokoda Track, delaying the advance of Japanese troops for long enough to await the reinforcement from the AIF and the US.
Following the crucial roles the militia played in protecting Australia's shores, the Defence (Citizen Military Forces) Act 1943 was put into place to allow the transfer of units to the AIF if more than 65 per cent of their personnel had volunteered for overseas service, as well as being able to call upon the militia to serve anywhere south of the equator in the south-west Pacific region.
Of the 575,799 Australians that served overseas in the Second World War, 39,429 were killed, 66,563 wounded and 30,000 were taken prisoner, with two-thirds of those being captured by the Japanese during their advance through south-east Asia.
Over a third of prisoners taken by the Japanese in World War II, died in captivity.
Following the surrender of Germany and Japan in 1945, there was still plenty of work to be done for the Australian Army.