Before "the incident" David had two major goals: to rise up in the ranks of the Air Force, and to retire at 55. He worked his way up to sergeant; that's one milestone. But he won't reach the second. He'll be medically discharged in October at the age of 50. He'll never serve again and he is unlikely to ever work again.

"I was ten-foot tall, bulletproof, nothing could get in the way of what I wanted to achieve." David speaks softly and looks you straight in the eye. He's a good talker. We are sitting in a common room in a hospital in Melbourne, which has been his home for three weeks. David is wearing grey tracksuit pants and a black Def Leppard T-shirt. He's sporting thongs and a moustache.

He's here because life began to unravel. David says it was like a seal on a pipe; it began to leak and once it started, it wouldn't stop. After holding off doing anything about it for a while, the wake-up call came from his wife, Deborah. "She said, 'If you keep on talking to me like I'm a piece of shit, I'll leave.'"

David takes me back to 2004. Two years into his second stint in the Air Force, an incident changed his life forever. He tells me details of that day, the face he sees every day in his nightmares. I can't share that part of his story but I can see why it haunts him. It took six years for the trauma to surface but its personality had already started to show itself: anger, disconnection from his wife and children, depression. "It was buried very deep in the back of my brain." It took a car hitting a metal plate behind him - a random sound and event - to bring it to the surface. "Suddenly I was lying on the ground, crying, I was a mess."

David was diagnosed with severe post-traumatic stress disorder (PTSD) - an illness so powerful that it can take everything away from a person and render the strongest of men helpless. It breaks apart marriages and causes collateral damage to children. But there are ways to proactively treat it.

David has already been through a 12-week outpatient PTSD program but now he's an inpatient in Ward 17 of Melbourne's Heidelberg hospital, along with another dozen or so men. It's where current and former servicemen and women come when they've hit rock bottom. David's here because he needs some specific help: he couldn't bring himself to fill in the paperwork for a medical discharge. His time here is helping him come to terms with what his life is now, and to give him the tools to look ahead to an undefined future.