The psychological assessment of navy divers, who were routinely exposed to trauma and deployed to war zones, was just a "tick and flick" exercise, an inquiry has been told.

Former captain Michael Maley said during his more than three decades of service he worked in extremely dangerous conditions.

Divers were required to deal with improvised explosive devices, clear mines, recover bodies and 음식물분쇄기 clear debris from ships, working at depths as low as 90 metres.

Mr Maley said he spent a total of 11 years at sea and more than two years in war zones, sometimes going 72 hours without sleep.

By the time his daughter turned 21, he had missed 17 of her birthdays.

But when he returned from deployments the checks on his mental health were brief and conducted too soon, he said.

"I had four, 15-minute psychological interviews which I believe were just tick and flick," he told the Royal Commission into Defence and Veteran Suicide on Thursday.

"You're still hypervigilant. You've just come out of theatre two or three days ago and you don't realise you have problems.

"You're not in a position to answer truthfully."

Mr Maley said he had also feared disclosing any mental health issues, which could lead to the loss of his security clearance.

Those same fears were expressed by other divers, including Ashley Semmens who said he went outside defence for support because of concerns over losing his career.

Mr Semmens told the commission of his own mental health struggles including PTSD, survivor's guilt and depression.

His concerns began following the suicide of a friend he had trained with and escalated after near-fatal injuries to fellow diver Paul De Gelder in a shark attack in Sydney Harbour in 2009.

That incident left him with a significant fear of going back into the water.

After hiding his own issues for about 15 years, Mr Semmens said "the option of suicide was there", though he ultimately decided he had too much to live for and a family who needed him.

But he said his efforts late in his military career, and subsequently as a civilian, to have the navy deal better with mental health issues among divers had largely been rebuffed.

He had no optimism that his call to action would be heeded.

"It's one of those things that it's kind of the topic of the week or the topic of the day," he said.

"Tomorrow there will be another topic, and that will be put through the shredder and forgotten about."

The lack of action by the navy both disappointed and angered him and made him scared for the divers still working.

Another diver Jeremy Thomas, who was on the scene when Mr De Gelder was attacked and helped save his life, said he lost trust in the navy when it failed to implement a recommendation from an investigation for tourniquets to be included in safety equipment.

He also told of his own experience with mental health problems, especially after he was injured by an IED in Afghanistan.

He said he wasn't frank in a psychological assessment out of a desire to get back to his unit so as not to let his colleagues down.

In other evidence, the commission was told of the high rates of suicide among navy clearance divers.

In one year, three took their lives.

Over the period of about a decade, there were eight deaths as well as a number of other attempted suicides.

Mr Semmens said he had lost four friends.

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