The 22-year-old pilot officer knows he is lucky to be alive. Most people wouldn't survive the injuries he suffered in a military bus accident almost three years ago.

The moment he crosses the finish line at this month's Invictus Games in athletics, swimming and indoor rowing, Costelloe will finally take his life back into his own hands.

Costelloe was sleeping on a bus returning from a week-long ADFA leadership field phase in November of 2015 before the vehicle rolled on Sandy Point Road, Windellama, about 50km south-east of Goulburn.

He woke to see the bus falling on its side with his head plummeting towards the gravel in a crash that left 12 people hospitalised.

"My head was dragged along the ground, I broke bones in the left side of my face, lost about a 10x10 centimetre squared area of my scalp which was ripped off," Costelloe said.

"Apparently I was awake for the whole hour but I don’t remember anything. It’s something to do with traumatic amnesia, where the pain is that great it forces the brain to forget it, just to protect itself from painful memories.

"My heart had stopped about 70 minutes in, I was resuscitated, I was airlifted out, and then I was in hospital shortly afterwards.

"A degloving of the scalp injury, it’s usually fatal because there is no mechanism for the body to clot blood or stop the bleeding.

"I know I’m very lucky to be alive, and I know when I was in hospital I gave it everything I could give to recover as quickly as possible. I was proud of myself."

Costelloe refused to stay in hospital for the recommended month - he found the place depressing. He refused strong painkillers, which made his stay more hellacious, and told staff to wheel him into a theatre whenever one opened up.

Twelve days, four surgeries and 156 staples later, Costelloe was back at ADFA watching a parade - "it was one hell of a roller coaster, that’s for sure."

A roller coaster that made Costelloe's graduation from ADFA in 2016 even more special after a turbulent first year upon which he looks back and labels himself "an alcoholic shitfight".

Squandered opportunities and growing frustration about his behaviour saw Costelloe issued a notice to show cause for termination. He knew he needed to turn things around.

"I had to give them reasons for why I shouldn’t be kicked out. I gave them the reasons and they were happy with it, so I was given a second chance but I was on thin ice," Costelloe said.

"I had to make the most of second year. I absolutely smashed it, I was in the top third of my cohort, I had won back the respect of my colleagues, I wasn’t a shitfight to them anymore. The staff had a better idea of what I was capable of.

"Then the accident came, and that pretty much removed all the progress that I did. I knew as soon as the accident occurred, I’m not going to let that get in the way of how far I had come."

Costelloe graduated with his cohort and wore his graduation ring and new ranked slides with pride. He won't be in the military come the end of the year, but he beams he will forever be a graduate of ADFA.

He is already preparing to be medically discharged as he continues treatment for his head injury in the hope he can continue to manage his emotions and find a way to sleep better.

Costelloe is now completing a masters in business - a great thing to say, but he laughs he despises himself for choosing more study.

But first? Competing in the Invictus Games, and getting his life back.

"When I cross that finish line, it will represent me taking control of my life again and everything that is given to me. That’s what Invictus is about," Costelloe said.

"Yeah, a gold medal would look really nice. Heck, it might bring out the blue in my eyes, but I will not be disappointed with myself if that is not the case.

"I have already won, and I am yet to even compete."

Brigid Baker is "absolutely petrified" about what this month has in store. It might not be something to take solace in, but at least she knows she has been through far worse.

Baker, who joined the Australian Army Reserves as a medic in 2002 and then moved into intelligence, had just been told she would be medically discharged when she found herself staring at her computer screen, "wondering what on earth I was going to do with myself".

Completely lost and isolated, Baker's sense of belonging had been whisked away after 15 years of service in Australia and Afghanistan.

The things she saw in Afghanistan sparked her bout with post-traumatic stress disorder, anxiety and depression, illnesses she hid from family and friends for months.

Then she saw a link for the Invictus Games. Petrified, yes, but buoyed by the experience of her past, Baker has finally rediscovered her sense of belonging.

"I was very surprised at what I was capable of doing physically and mentally," Baker said as she prepares to compete in athletics and powerlifting.

"To know your perceived limitations aren’t your actual limitations, to have that in my back pocket coming into the Games is a handy thing to have.

"You have a little more confidence in yourself and your abilities, knowing ‘I’ve been through worse’."

Ruth Hunt refuses to be defined by cancer.

"I don’t want cancer to be at the centre of my world. It’s just something that unfortunately happened to me and I’m over it, it’s time to go back and be normal again," the army law officer said.

For her, Invictus Games is a platform to be normal again. It has been a year in the making, with Hunt balancing training with work and undergoing cancer treatments during her lunch breaks.

Now she has no sign of disease, but Hunt's aggressive breast cancer means she won't technically be in remission for three years.

But it was by no means an easy road - look no further than the start of her training for swimming and indoor rowing for proof.

"I got a little bit frustrated at the start when after my surgery because I couldn’t swim the way I used to and I ended up being in the slowest lane, which I don’t think I’d ever been in in my time swimming," Hunt said.

"I was at the back of the slow lane, and I just knew there was this mountain of work ahead of me, but it motivated me to keep going to training.

"I just had to balance it - if I wasn’t feeling well enough to train then I just the decision that I wasn’t going to train.

"That was just part of the process, and I would just have to deal with that and not get too worked up because I wasn’t going to training.

"I applied in October last year, it has been almost a year of training and camps and stuff, and now I am keen to race."