It's near impossible to imagine 22,000 men creeping undetected over soil frozen so hard it rings with the mere step of a boot.
How could such a multitude shuffle downhill in the night to an exposed beach, the moon almost full in a cloudy sky, there to clamber aboard boats and head out to sea without alerting an enemy perched on ridges directly above; an enemy that had grown over months to know the rhythms and the sounds of all those men on the slopes below them?
Bill Scurry's tinny idea that worked.
Here was the problem for commanders given the task of evacuating all remaining Anzac forces from the Gallipoli peninsula on just two nights: December 18–19 and 19–20, 1915: precisely 100 years ago.
Gallipoli for the invaders and the defending Turks had become less a battle against each other than a battle against disease and the elements. Frigid wind tore at their worn-out clothing. Frozen earth robbed them of sleep.
From September, one in 13 Australian and New Zealand men on Gallipoli were evacuated on the sick list every week. Only twice during the whole hopeless campaign – in May and again in August, when the fighting was intense – did the proportion of those being taken off suffering wounds from bullet or bomb exceed the rate of those removed suffering illness.
"Of the men still holding the trenches," wrote military historian Ross Mallett in his 1999 masters thesis at the Australian Defence Force Academy, "77 per cent were emaciated, 78 per cent had diarrhoea and 64 per cent had skin ulcers, known to the Diggers as Barcoo rot."
By December, men who had suffered through summer's swarms of disease-carrying flies, lice and rats now froze to death. Many had such severe frostbite their toes and fingers had to be amputated. There was no longer any point staying – if there had been any point being there at all.
As word of the coming retreat filtered around the shivering hills, a young Melbourne fellow, a mere lance-corporal aged 20 named Bill Scurry, thought hard about how the Turkish forces might be lulled into the belief that nothing unusual was happening.
He was an architectural modeller by trade, but like everyone on Gallipoli, guns had become an extension of his being.
"It occurred to me that if we could leave our rifles firing we might get away more surely," Scurry wrote later. "At that time I don't think anybody dreamed that we would all get away." Quite.
No one believed the campaign – an eight-month disaster achieving nothing but a lasting legend – could end without further blood. Commanders figured deaths were likely to be as high as 30 per cent.
Vice-Admiral John de Roebuck, commanding fleet operations, wrote that such was the potential for calamity, plans had been made to "negotiate an armistice in the morning after evacuation to collect, and if possible, bring off our wounded".
But young Lance Corporal Scurry had dreamed up a rifle that would fire as the men crept away. Having experimented unsuccessfully with an idea taken from sand through an hour-glass, he hit on the concept of dripping water. He rigged up a rifle connected to two ration tins.
One tin, filled with water and a small hole in the bottom, was suspended above another. As water dripped, it began filling the tin below, which was connected to the rifle's trigger by string. After 20 minutes to an hour, the weight of the water caused the bottom tin to overbalance, its string snapping the rifle's trigger.
A lance-corporal needed a powerful friend if he wanted his wild idea to be taken seriously. Back in Melbourne, he and a man who would become one of Australia's great military leaders, Pompey Elliott, had both belonged to the 58th Infantry, known as the Essendon Rifles. Elliott was now commander of the the 7th Battalion on Gallipoli – Scurry's unit.
Elliott was much taken by the self-firing rifle. He promoted it among the brass and ordered more to be made. Ninety-six such devices were fashioned: 12 for each of eight battalion fronts.
And in the eerie early hours of the final night, as thousands of men, their boots muffled in hessian bags and socks, shuffled over blankets laid on frozen ground in trenches, down tracks already broken with picks, to piers carpeted with sacks, the sound of Scurry's "pop-off" rifles could be heard, just like every other night on Gallipoli.
By dawn, the Anzacs were gone. Not a single man had been killed or wounded. Bill Scurry went on to the Western Front where he became a Major, lost an eye and part of his hand while examining a German bomb and came home with a Military Cross to grow berries on a soldier settler's plot at Silvan in the Yarra Ranges. He died in 1963.
Tomorrow, Sunday, December 20, he will be remembered at a ceremony at his graveside at the Lilydale Lawn Cemetery. A plaque will be unveiled, Scurry's daughter, Judith Storey, will attend and the Speaker of the Australian parliament, Tony Smith, will address the crowd.
A century on, Turks argue their fighters were happy to see the backs of the Anzac invaders and simply let them go.
In Australia, Bill Scurry will always be regarded as the man who conceived the idea that saved the last Anzacs of Gallipoli.
Tony Wright is the associate editor and special writer for The Age and The Sydney Morning Herald.