Sing began his military career as part of the Australian and New Zealand Army Corps (ANZAC) forces in the Gallipoli Campaign in modern day Turkey.
Biographer John Hamilton described the Turkish terrain thus: "It is a country made for snipers.
The Anzac and Turkish positions often overlooked each other.
Each side sent out marksmen to hunt and stalk and snipe, to wait and shoot and kill, creeping with stealth through the green and brown shrubbery ..." Sing partnered with spotters Ion 'Jack' Idriess and, later, Tom Sheehan.
The spotter's task was to observe (spot) the surrounding terrain and alert the sniper to potential targets.
Idriess described Sing as "a little chap, very dark, with a jet black moustache and goatee beard.
A picturesque looking mankiller.
He is the crack shot of the Anzacs."

Chatham's Post, a position named after a Light Horse officer, was Sing's first sniping post.
Biographer Brian Tate wrote, "It was here that Billy Sing began in earnest his lethal occupation."
He set about his task with a Lee–Enfield .303 rifle.
An account by Private Frank Reed, a fellow Australian soldier, states that Sing was so close to the Turkish lines that enemy artillery rarely troubled him.
His comrades left three particular enemy positions to his attention: a trench at 350 yards (320 m) from his post, a communication sap at 500 yards (457 m), and a track in a gully at 1,000 yards (914 m).
According to Reed, "Every time Billy Sing felt sorry for the poor Turks, he remembered how their snipers picked off the Australian officers in the early days of the landing, and he hardened his heart.
But he never fired at a stretcher-bearer or any of the soldiers who were trying to rescue wounded Turks."
In contrast, Hamilton said in a 2008 interview, "We have an anecdote where, after spotting an injured Turk, he said 'I'll put that poor cuss out of his agony' and just shot him.
He was a very tough man."

Sing's reputation resulted in a champion Turkish sniper, nicknamed 'Abdul the Terrible' by the Allied side, being assigned to deal with him.
Tate alleges that the Turks were largely able to distinguish Sing's sniping from that of other ANZAC soldiers, and that only the reports of incidents believed to be Sing's work were passed on to Abdul.
Through analysis of the victims' actions and wounds, Abdul concluded that Sing's position was at Chatham's Post.
After several days, Sing's spotter alerted him to a potential target, and he took aim, only to find the target—Abdul—looking in his direction.
Sing prepared to fire, trying not to reveal his position, but the Turkish sniper noticed him and began his own firing sequence.
Sing fired first and killed Abdul.
Very shortly thereafter, the Turkish artillery fired on Sing's position—he and his spotter barely managed to evacuate from Chatham's Post alive.

Near the beginning of August 1915, Sing was hospitalised for four days with influenza.
That same month, an enemy sniper's bullet struck Sheehan's spotting telescope, injuring his hands and face, and then hit Sing's shoulder, but the latter was back in action after a week's recuperation.
Sheehan was more severely wounded, and was shipped back to Australia.
This was reportedly the only time that Sing was injured at Gallipoli.
He would not fare so well later on in the war.
Sing began his military career as part of the Australian and New Zealand Army Corps (ANZAC) forces in the Gallipoli Campaign in modern day Turkey. Biographer John Hamilton described the Turkish terrain thus: "It is a country made for snipers. The Anzac and Turkish positions often overlooked each other. Each side sent out marksmen to hunt and stalk and snipe, to wait and shoot and kill, creeping with stealth through the green and brown shrubbery ..." Sing partnered with spotters Ion 'Jack' Idriess and, later, Tom Sheehan. The spotter's task was to observe (spot) the surrounding terrain and alert the sniper to potential targets. Idriess described Sing as "a little chap, very dark, with a jet black moustache and goatee beard. A picturesque looking mankiller. He is the crack shot of the Anzacs."
Chatham's Post, a position named after a Light Horse officer, was Sing's first sniping post. Biographer Brian Tate wrote, "It was here that Billy Sing began in earnest his lethal occupation." He set about his task with a Lee–Enfield .303 rifle. An account by Private Frank Reed, a fellow Australian soldier, states that Sing was so close to the Turkish lines that enemy artillery rarely troubled him. His comrades left three particular enemy positions to his attention: a trench at 350 yards (320 m) from his post, a communication sap at 500 yards (457 m), and a track in a gully at 1,000 yards (914 m). According to Reed, "Every time Billy Sing felt sorry for the poor Turks, he remembered how their snipers picked off the Australian officers in the early days of the landing, and he hardened his heart. But he never fired at a stretcher-bearer or any of the soldiers who were trying to rescue wounded Turks." In contrast, Hamilton said in a 2008 interview, "We have an anecdote where, after spotting an injured Turk, he said 'I'll put that poor cuss out of his agony' and just shot him. He was a very tough man."
Sing's reputation resulted in a champion Turkish sniper, nicknamed 'Abdul the Terrible' by the Allied side, being assigned to deal with him. Tate alleges that the Turks were largely able to distinguish Sing's sniping from that of other ANZAC soldiers, and that only the reports of incidents believed to be Sing's work were passed on to Abdul. Through analysis of the victims' actions and wounds, Abdul concluded that Sing's position was at Chatham's Post. After several days, Sing's spotter alerted him to a potential target, and he took aim, only to find the target—Abdul—looking in his direction. Sing prepared to fire, trying not to reveal his position, but the Turkish sniper noticed him and began his own firing sequence. Sing fired first and killed Abdul. Very shortly thereafter, the Turkish artillery fired on Sing's position—he and his spotter barely managed to evacuate from Chatham's Post alive.
Near the beginning of August 1915, Sing was hospitalised for four days with influenza. That same month, an enemy sniper's bullet struck Sheehan's spotting telescope, injuring his hands and face, and then hit Sing's shoulder, but the latter was back in action after a week's recuperation. Sheehan was more severely wounded, and was shipped back to Australia. This was reportedly the only time that Sing was injured at Gallipoli. He would not fare so well later on in the war.
Billy Sing