But a single meeting derailed his shining 26-year career.

In 2006 he walked into his superior’s office and admitted he had been diagnosed with post-traumatic stress disorder.

“I spoke three languages. I was familiar with people of significance in foreign countries. I understood how those countries worked, what their procedures were, what they thought about things," he said.

“And yet the system was quite prepared to just toss me onto the junk pile and say, ‘see you later’.”

After working on international peace missions, running an entire army’s communications in war zones and picking through earthquake rubble, Colonel Carey suddenly found himself with little else to do than mow his lawn.

He was aware there were countless others in similar circumstances - soldiers sitting at home, frustrated and lost, completely cut off from their powerful support system.

Those soldiers were at increasing risk of suicide and self-harm.

From 2001 to 2016, there were 373 suicides in serving, ex-serving and reserve ADF members.

Across 2014-16, young ex-servicemen aged under 30 had a suicide rate more than twice that of non-serving men in the same age group.

For Colonel Carey, the trauma thousands of his colleagues have experienced in the sharp and disconcerting break from military life to civilian is real, damaging, and needs to change.

At a recent Brisbane hearing for the joint parliamentary inquiry into the transition from the Australian Defence Force into civilian life, the former officer detailed a concept for a full-scale regiment of these medically discharged soldiers serving in relief and emergency aid projects - a Black Dog Regiment.

The regiment would sit within the current Australian Defence Force, providing a clear transition process over several months for servicemen and women who were being medically discharged.

The regiment would also include emergency services personnel such as police and firefighters who had also suffered mental injury.

From disaster response and support for regional communities struggling with infrastructure woes, to labour for drought-stricken farmers, the chance to use former servicemen and women would not only benefit Australia, but the soldiers as well, the former officer argued.

During that transition they would be deployed across the nation in practical projects with professional psychiatric and social worker support.

Setting the regiment within the existing Defence structure would cost, Colonel Carey said, but the pay-off would outweigh the immediate financial outlay.

Speaking to Fairfax Media after the hearing, he said the driving motivation behind most soldiers joining the Defence force was simply to serve their country.

“The skills that we have are universal. Soldiers aren’t just mindless creatures that run up hills and shoot people,” he said.

“Most soldiers are carpenters, electricians, plumbers, medics, pilots, truck drivers.

“We spend hundreds of thousands, if not millions of dollars, training these people, and the second that there’s some sort of issue healthwise - gone.”

There are already small projects where former servicemen and women with traumatic mental and physical injuries are sent as community contributors, including a recent program in Townsville’s ex-ADF support organisation The Oasis.

The Oasis is sending small groups of veterans to assist drought-stricken farmers with free labour, skilled technicians and support to Winton, north of Longreach.

Colonel Carey’s vision is on a far larger scale.

It was after responding to earthquakes in Papua New Guinea in 1992 that he suffered his first symptoms of PTSD.

Continuing to rise through the ranks, working internationally and on Australian soil in numerous prominent leadership positions, he played key roles in war zones and peace missions, training colleges and communications.

Serving in the early years of the Afghanistan war, still with his PTSD undisclosed, then-Major Carey ran the Army’s entire communications network for six months.

“The wheels fell off” when he was sent directly from Malaysia back to Papua New Guinea as the Deputy Head of the Australian Defence Force.

“I got PTSD in PNG, and I always had it in the back of my mind that if I went back there one day, and I could smell it and taste it, I could fight this,” he said.

“But I went back there and I smelt it and I tasted it, and I fell apart.

“So the boss said 'best you quit.'”

Now retired, Colonel Carey is still determined to see change to protect others like himself from falling through the cracks, their skills and experience wasted.

Finding his own support through the years since he left the military, he developed a network of fellow medically discharged former servicemen and women, supporting each other through social media.

That small group of contacts has proved critical.

“We’ve already saved two lives,” he said.

Like him, those veterans want to see their skills put to use, their experience once again serving the nation, rather than being left flailing in mental pain.

“We’ve got to get over this mindset that if you’re not for the military you’re not good, full stop,” Colonel Carey said.

The parliamentary inquiry continued hearings around the country in October.

If you require help or support, contact Lifeline on 13 11 14.