The convoy left the Western Australian town of Albany on November 1, 1914, carrying 20,000 Australian and 8,500 New Zealand soldiers bound for Gallipoli in modern day Turkey and later the battlefields of Europe.
"It was a heavy day in our history and it led to even heavier times to come," Australian Prime Minister Tony Abbott said in remarks welcoming New Zealand leader John Key to the country.
"The first World War was the crucible in which the Australian identity was forged. In 1914 we were a country with a flag and a parliament but little sense of nationhood.
"The baptism of fire that was the Great War changed all that. The scale of sacrifice and loss was beyond anything imaginable."
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Losses in Gallipoli were hard, with the offensive claiming the lives of more than 11,000 New Zealand and Australian troops in a matter of months, although worse battles were to follow in the Great War, Key said.
"But the service, and sacrifice, of those who fought for us -- would play a critical role in forging our national identities.
"Our experiences in the First World War marked an important point in our coming of age as countries. They made us look at who we were, and we came from colonies to became nations," Key said.
Before the service thousands had lined the streets of Albany for a commemorative troop march, ahead of a symbolic departure of a flotilla of naval warships from King George Sound.