Sergeant Ian Turner was found dead in his Sydney home in July 2017 in the months following his final deployment to Iraq, which was only made possible after his company commander intervened to have a refusal of medical clearance reconsidered.

The inquest has heard the defence force was absolutely aware Sgt Turner had developed post-traumatic stress disorder years earlier, turned to alcohol to cope, and began abusing his wife and harming himself.

In his second day of evidence before the Sydney inquest on Thursday, Lieutenant Colonel AF reiterated that he had intervened to see Sgt Turner deployed on his final Iraq tour because it was "in his best interest".

Sgt Turner's mental health had been getting "better and better" during 2016, his self-worth was tied to his ability to deploy and the tour would give him six months away from alcohol and his deteriorating relationships at home, he had argued.

However, the inquest has heard Sgt Turner's colleagues were concerned about his ongoing PTSD symptoms, that he was rumoured to have smuggled alcohol onto the base in his previous deployment and had originally been deemed at high risk of deterioration should he undertake the tour.

He was deployed without a mental health care plan because Lt Col AF didn't see it as necessary, and was not provided with immediate psychiatric intervention after several incidents on tour which greatly distressed him.

Given the evidence, Lt Col AF was on Thursday given the opportunity to reconsider some of comments he made earlier in the inquest.

"You've said ... 'There's a point where I think the organisation didn't fail him, for lack of a better term, and, this is harsh, he failed the organisation'.

"Do you think that you might walk back from that comment with the benefit of hindsight?" a lawyer acting for Sgt Turner's parents asked.

"No, I don't walk back from those comments," Lt Col AF replied.

"Ian was a friend of mine and he was a good soldier, but he was also an adult, and adults are responsible for their decisions and actions."

When asked how exactly Sgt Turner failed the defence force, Lt Col AF said it was a "tough question".

"The answer is, suicide is unacceptable."

"Killing yourself is an unacceptable course of action and Ian should not have done it."

He argued Sgt Turner had the "tools" to beat his challenges despite his deteriorating mental health and substance abuse.

"He was very intelligent and had the tools and the support network to work through what was a challenging and complex time for him at work, but more, more importantly, in his personal life."

"Do you not accept that by reason of his mental health problems, he didn't have the tools to work through those challenges," counsel assisting the coroner Kristina Stern asked.

All Sgt Turner had to do was ask for psychiatric help, Lt Col AF said.

"The defence force's mental health network was there for him to use."

The coronial probe, overseen by Deputy State Coroner Harriet Grahame, will consider whether the defence force appropriately managed Sgt Turner's welfare in the lead-up to his death.

The inquest comes as a royal commission into veteran suicides is set to begin, to investigate why the rates of suicide for ex-services personnel are much higher than in the broader Australian population.

Australian Associated Press