General Angus Campbell will take the stand for the second time during the inquiry, having previously given evidence at a 2022 hearing in Townsville.

Royal Commission chair Nick Kaldas said General Campbell's appearance on Thursday would be an opportunity to determine what cultural and systemic challenges the inquiry had identified within defence.

"Nearly two years ago, General Campbell admitted defence was not doing enough to address this national tragedy," Mr Kaldas said.

"We're keen to hear what urgent steps defence has taken in the intervening period to improve health and wellbeing outcomes for its people."

The army, navy and air force chiefs have previously given evidence to the commission.

Mr Kaldas said the tri-service chiefs had acknowledged suicide and suicidality as a service issue and spoke openly about improvements needed within defence.

"It was particularly good to hear the chiefs of air force and navy acknowledge there is a link between what happens during service and the adverse outcomes some experience after they leave the military," he said.

"This is something defence has not previously acknowledged, believing that this was a problem mainly for those who have left service and therefore for the Department of Veterans' Affairs."

On Tuesday, the commission will hear evidence from Department of Defence secretary Greg Moriarty.

A final report is due to be delivered to the governor-general by September 9.

Australian Associated Press