William McCann, who appeared on Tuesday morning before the commission in Hobart, was medically discharged from the army in 2019 after 13 years, due to struggles with post-traumatic stress disorder.

He said he had benefited from a great support network, a medical network and supportive family since his diagnosis.

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"Despite that, throughout my time dealing with mental condition and post deployment, I have suffered with almost persistent suicidal ideation, culminating in points where I have actively plan my own suicide," Mr McCann said.

He was part of an observer unit deployed to Sinai in Egypt in 2015 in what was understood to be a peacekeeping role.

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Mr McCann said a two-week training course could not have prepared the team for what they were to experience.

He said on arrival, the security situation had deteriorated greater than anticipated as Islamic State elements increased hostilities against the Egyptian forces.

"It escalated to a point that we started seeing direct attacks on our camp," he said.

"Whether or not these were directly targeted us in order to draw out other forces, we were still being targeted."

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On his return from his deployment, he said things started to deteriorate for him.

Mr McCann said he was later surprised to learn that he had post-traumatic stress disorder - something he expected could be related to a peacekeeping mission.

He said the diagnosis made him feel ashamed, weak and he was worried that colleagues perceived that he was faking his mental condition.

"I was afraid to accept my conditions, I was afraid to get help," Mr McCann said.

"I was fearful of being mocked or invalidated by others.

"I believed I was a failure, not worthy of being a soldier or an officer, let alone being a husband and a father.

"I believed I was not worthy to be alive."

He said the defence force had a good culture of support amongst officers and access to services was adequate for people while they were employed, but it was a struggle to get the same level of help once discharged.

The final day of Royal Commission hearings will be held in Hobart on Wednesday.

The commission is scheduled to release an interim report on the inquiry on Thursday.