This week marks 100 years since the World War I battles of Fromelles and Pozieres — two of the deadliest and most gruesome in Australia's military history.

Sorry, this video has expired The battles of Fromelles and Pozieres: 100 years on

In an attempt to feint and distract German forces who were battling the French and British on the Somme in the south, Australian forces were sent into Fromelles, about 100 kilometres north, at 6:00pm on July 19, 1916.

It was Australia's introduction to the Western Front — the main theatre of the war — after spending months fighting in Gallipoli, and the results were disastrous.

Fromelles: 'Don't forget me, cobber'

A shell explodes on the battlefield at Fromelles. ( ABC TV )

It is estimated there were some 5,500 Australian casualties on the first day — the greatest loss in a single day in Australia's history.

By 8:00am the next morning the Battle of Fromelles was over, with Australian forces forced to withdraw.

A bible page with passages underlined that was unearthed in 2009. ( Commonwealth War Graves Commission )

The Australian War Memorial refers to the offensive as "the worst 24 hours in Australia's entire history".

"Practically all my best officers are dead," said senior officer General Harold Edward 'Pompey' Elliott, who described Fromelles as a "tactical abortion".

"I presume there was some plan at the back of the attack but it is difficult to know what it was."

A number of factors set the Western Front apart, explains Joan Beaumont, a WWI historian at the Australian National University.

"One was the sophistication of the trench system and the scale of the battle compared to Gallipoli, which was much more confined," she says.

"But more notably, the Western Front was a battle that was very much determined by heavy artillery, and the Germans had a much higher level of skill and weaponry at hand."

Australian troops prepare for the attack on Fromelles. ( AWM )

The heavy artillery and organisation employed by the Germans, along with gruesome scenes of body parts strewn across the battlefield, had a shocking effect on the Australian troops, who were almost entirely civilian volunteers with limited military training.

The famous phrase "Don't forget me, cobber" originated in Fromelles, when it was shouted by a wounded soldier at Sergeant Simon Fraser — who reported on the aftermath in a letter home — during a rescue mission.

It has also been established that 27-year-old Corporal Adolf Hitler was amongst the Germans in Fromelles fighting the Australians.

Pozieres: 'My friends are raving mad'

An Australian fatigue party passes a German bunker at the western end of Pozieres. ( Australian War Memorial )

Just days later, at 12:30am on July 23, Australian forces were sent to join the British and French allies in the small town of Pozieres along the Somme, for another battle that would make records as one of Australia's deadliest.

Australian soldiers walk back to their billets after fighting on the frontlines in Pozieres. ( AWM )

Although the six-week battle for Pozieres was somewhat a success, with allied forces taking over the town, there were some 23,000 Anzac casualties, a figure comparable to the 28,000 suffered during the eight months spent fighting in Gallipoli.

Australian WWI correspondent Charles Bean famously reported the Pozieres ridge was "more densely sown with Australian sacrifice than any other place on Earth".

"The men were simply turned in there as into some ghastly giant mincing machine," he later wrote.

The Australian War Memorial — which was conceived by Bean during the 1916 battles — says that "for men thrown into the fighting at Pozieres, the experience was simply hell".

"My tunic is rotten with other men's blood, and partly splattered with a comrade's brains. It is horrible, but why should you people at home not know?" Lieutenant John Raws later wrote.

"Several of my friends are raving mad. I met three officers out in No Man's Land the other night, all rambling and mad."

The two battles served as a cruel introduction to the harshness of the war on the Western Front, and as word of the gruesome battles got out volunteer numbers began to fall.

Professor Beaumont explains: "there's no doubt that Australians back home were very aware of how terrible the casualties in Fromelles and Pozieres were."

"The scale of losses are essentially what triggered the subsequent conscription debates, and the nature of those battles made the debates extremely emotional."

Conscription referendum of 1916 defeated

In early September, Australian divisions were taken out of the main battle in Pozieres to recover and rebuild their strength.

With volunteer numbers dropping, Australian prime minister Billy Hughes moved to hold a referendum on whether or not overseas conscription should be mandatory.

A WWI recruitment poster. ( AWM )

Until that point, only military service was mandatory for Australians.

Hughes had long wanted to introduce conscription, rather than voluntary recruitment, but could not get the support in the Government, so on October 28, 1916, Australians were asked:

"Are you in favour of the Government having, in this grave emergency, the same compulsory powers over citizens in regard to requiring their military service, for the term of this War, outside the Commonwealth, as it now has in regard to military service within the Commonwealth?"

The referendum was narrowly defeated — 51 per cent against versus 49 per cent for — with many attributing reports of the Battles of Fromelles and Pozieres as the reason.

But Australians remained bitterly divided over the issue.

"There were lots of reasons why Australians voted no, ranging from labour unions fearing conscription would hand jobs over to immigrants, to libertarians outright saying it's not right to force a man to kill," Professor Beaumont says.

"But the meetings and debates became quite violent. Everyone knew who had served and who hadn't in their communities, and people would get on tables and name names.

"It is by far one of the fiercest debates in Australia's history."

One of the consequences of the debates that lingers in Australia today, Professor Beaumont says, "is the entrenched belief that you could not conscript men to fight overseas" — an issue that was touched upon again in subsequent wars.

Nonetheless, 1916 — through the Battles of Fromelles and Pozieres — is widely seen as the first year Australians played a full role in WWI, and although many of that year's offensives did not achieve their goals, they helped deal significant blows to German forces.