Ben Roberts-Smith has maintained his composure while questioned over claims he committed war crimes in Afghanistan, insisting he did "everything in my power" to complete a mission to capture or kill rogue Afghan insurgent Hekmatullah in 2012.
Mr Roberts-Smith, 42, is in the witness box for his first day of cross-examination at the Federal Court defamation trial launched against the publishers of three newspapers he claims defamed him in articles from 2018 by painting him as a criminal who broke moral and legal rules of military engagement.
The war hero is also suing over claims he assaulted a woman in Canberra.
He denies all the claims against him while the publishers of the Sydney Morning Herald, The Age and The Canberra Times are running a truth defence.
On Thursday, the respondents' barrister Nicholas Owens SC asked Mr Roberts-Smith whether he wanted to leave "no stone unturned" on a mission in Darwan in 2012 in a search for Hekmatullah, who had recently murdered three Australian soldiers.
"I was going to do everything in my power to complete the mission," Mr Roberts-Smith said.
The court heard that the search to either kill, capture or gain intelligence from Hekmatullah justified Mr Roberts-Smith risking his life to swim across the Helmand River, in Uruzgan province, by himself without body armour and then engage an insurgent who was hiding among boulders.
While Mr Roberts-Smith, in his evidence in chief, at times broke down in tears recounting details of his military service in Afghanistan, the two-metre tall war hero showed little sign of emotion on Thursday morning under questioning from the media outlets' lawyer.
The court has also heard evidence it was permissible for SAS troops to use "whatever force necessary" within the rules of engagement to get compliance from insurgents in Afghanistan, including at times punching persons-under control, known as PUCs, after arrest.
"If required, yes," Mr Roberts-Smith told the court.
"If they were fighting back you would use whatever force is necessary to put that person under confinement."
Earlier, the court was told that Mr Roberts-Smith understood that it was never permitted to kill or assault a PUC under the rules of engagement in Afghanistan or the Geneva Convention.
The decorated SAS veteran is likely to be cross-examined until at least Wednesday next week, the court heard.
Mr Roberts-Smith's legal team has previously argued that he is the victim of a lying campaign by failed soldiers envious of his stellar military career.
The trial has previously heard that he lost hundreds of thousands of dollars in income after his reputation was severely damaged by the media reports about his Afghanistan deployments.
The trial continues before Justice Anthony Besanko.
Australian Associated Press