But the former cadet's defence barrister said while it was not in contention that the two had sex, it was in dispute that the woman had not - by her words and conduct - consented.

The former cadet Harlan Agresti, 23, is charged with one count of sexual intercourse without consent. He has pleaded not guilty.

The jury heard the case is a retrial.

Mr Agresti and the alleged victim, who legally cannot be identified, were both 18 and first year officer cadets at the Australian Defence Force Academy in 2013, the ACT Supreme Court heard.

On June 22 that year, a Saturday night, a group of cadets went out drinking in Civic, including Mr Agresti and the woman.

The woman, whose evidence was a video recording from the earlier trial played to the court, said she told Mr Agresti she could not see properly and needed to go home.

She did not remember the taxi ride but remembered being supported and guided by Mr Agresti and vomiting in the garden while they walked to her room.

The next thing she remembered was lying on the bed with Mr Agresti on top of her and the two of them kissing and then having sex, she said.

She said before he left her room he told her it would be their secret, and she agreed. She told the court she was worried about rumours.

"I wouldn't under my normal character have slept with Agresti," she said.

The next morning she was "very, very sick".

She said she believed Mr Agresti had also been "very intoxicated."

Later, when messaging each other about the incident, she said Mr Agresti told her if she ever wanted to know what happened to ask him.

"I guarantee I remember it accurately," he said.

In an opening address to the jury, prosecutor Rebecca Christensen said the intercourse between Mr Agresti and the woman took place "when one was too drunk to consent."

"Mr Agresti was not the one too drunk," she said.

She said Mr Agresti had about five or six drinks that night, and the other cadet a lot more.

She told the jury the effect of the woman's intoxication was so substantial she was unable to consent and Mr Agresti knew that.

She said the two agreed to keep what happened a secret, but Mr Agresti left her room that night and told the first person he saw.

He told other cadets he had sex with the woman, and described the woman as "starfishing" during the act, the prosecutor said.

Mr Agresti's barrister Philip Dunn QC told the court in his opening address the woman did not report the allegation to the military until August 2014, more than a year after the incident.

He said that meant there was no surveillance footage of the night, and the court would rely on people's memories of events.

He flagged that among the matters in dispute were whether Mr Agresti believed the woman was consenting, whether rumours that the woman was a "bad root" got back to her, and if that upset her.

He asked the jury to consider whether human memory was like a tape record, or did it alter over time and if you had a certain view of things.

Justice Michael Elkaim warned the jury not to read or listen to any media reports of the case, and if they came across any, to ignore it.

The trial continues.