"People say 'So tell me what it was like', and it's an impossible question to answer. [For the soldiers] after eight months of driving out there into the desert and being engaged by an enemy, being involved in deaths so directly, there's no answer."

The embed in 2011 led to a collection of works titled that is now touring Australia. The portraits - huge, thickly textured canvases of visceral flesh and dark tones - show the human face behind the headlines about shootings, helicopter crashes and IED (improvised explosive device) strikes in Afghanistan.

Quilty says Afghanistan took him to the extremes of human experience, continuing his exploration of masculinity and what he describes as its "self-indulgent" rites of passage.

He was invited on very short notice, and deployed six weeks later. The pre-deployment training, which he describes as "emotional preparation" for some of the worst possible outcomes, was in itself an inspiration. "[It's] quite [a] confronting and very moving experience to sit in this big theatre with all these quite often really young people who are listening to this stuff with very real reason - they're going to Afghanistan."

Once deployed, Quilty says he tried to remain in the background, feeling out of place and way out of his depth as rockets sailed into Kandahar base at night and he lay "s***-scared" on a cot in an armoured shipping container.

The troops were intrigued by his presence, a welcome break from the monotony and adrenaline of their lives, and Quilty says he met "quiet, sensitive and normal" people.

The major question for Quilty was "why".

"They're 18 and they look like they can't even shave, [you want to ask] 'Does your mum know what you're doing? What are you doing here?'"

Some were following the family tradition, others were attracted to the emphasis on fitness, physicality and hierarchy, or had flunked school and saw military service as more respected and better paid than learning a trade. It was a sensitive topic - "why" was something they couldn't, or wouldn't explain.

"A lot of them wanted to get out … [but] there's no way they want their friends to hear that. It's destructive, you've got to keep your s*** together for everyone."

The pressure can boil over - once Quilty saw an all-in brawl break out over a hockey game in Kandahar, and he was warned to stay away from the US quarters, where women walked around "wearing bra tops with M16s slung across their shoulders, the guys have tattoos and big chains and M16s and sidearms".

There were also profound moments: soldiers doing a yoga class, going on patrol with a priest's blessing of the trucks at 3am. "Every time you see someone drive through those gates you wonder if they're going to come back."

Once back in Australia, Quilty found it difficult to reconnect with the experience and asked some of the men and women if they would come to his rural studio and sit for him. Bleak, stirring tales emerged.

"It was impossible to make a bad painting of those people. They're unbelievably powerful subjects, broken sometimes," he says.

Several men had been diagnosed with post-traumatic stress disorder; Quilty spoke to their psychiatrists to ensure he was doing the right thing by asking them to relive the events that scarred them so deeply.

"All of them said yes. It's been a really positive thing in an otherwise bleak year for these guys," he says.