General Angus Campbell gave evidence at the final public hearing day for the Royal Commission into Defence and Veteran Suicide.
"Our people deserve and should rightly expect the support and care they need both during and after their service," he said.
Angus Campbell says Defence has a "great deal of work to do" to win back the trust of veterans. (HANDOUT/ROYAL COMMISSION INTO DEFENCE AND VETERAN SUICIDE)
"I acknowledge that this has not always been the case and tragically it's led to the deaths by suicide of some of our people.
"Defence is committed, and I am committed to doing better.
"I apologise unreservedly for these deficiencies."
General Campbell said the courage displayed by those who came forward to share their experiences was deeply admirable.
"I sincerely appreciate the efforts of those who have contributed to my learning and our deeper understanding of suicide and suicidality and its enduring aftermath," he said.
The defence force chief said he and his colleagues who had served in the military for decades were committed to addressing the failures.
Asked about evidence presented earlier in the inquiry that highlighted an attitude of exceptionalism in the military, General Campbell said that perspective was rejected by the ADF as "deeply damaging".
"Those who might be seen by the public as most exceptional, are people who we expect to be most humble," he said.
Describing the alleged war crimes committed by Australian troops in Afghanistan as a "catastrophic failure", General Campbell rejected the argument that senior leadership hadn't taken responsibility.
"I stood up in front of our nation and took absolute responsibility and apologised to Australia, to all those defence personnel who were affected, and to those in Afghanistan who may be affected by the credible information of allegations of unlawful conduct," he said.
On tribalism, the head of the ADF said it was important for building cohesion and identity within a team to manage the stress of combat, but that it became an issue when tribalism stopped other teams from working with each other to form an integrated force.
General Campbell said Defence had a "great deal of work to do" to win back the trust of veterans who had been treated poorly.
He said the ADF had people attending the hearings every day, and of different ranks, so that the evidence given at the royal commission would flow through the military for generations to come.
General Campbell is the last and only witness appearing at the inquiry in Sydney on Thursday.
The Royal Commission will be adjourned after Thursday's hearing until the Ceremonial Closing Sitting in Sydney on August 28.
Its final report is due to be handed down in September.
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