The trial of Royal Military College cadet Jonathan David Hibbert, 26, began on Monday in the ACT Supreme Court.

The trial is expected to hinge largely on whether consent was withdrawn during what started as consensual sex, and whether Hibbert knew it had been withdrawn.

The complainant, a relatively new cadet at the officer training institution, had just taken part in her first Anzac Day march in regional NSW.

She told the court that the pride she felt while marching for her country had helped her overcome doubts about whether she belonged at Duntroon.

"I had a bit of a hard time," she said.

"There were definitely times when I doubted wanting to be there, I guess everyone did to an extent.

"Anzac Day was one of the best days of my life ... I sort of forgot the hard parts of my training."

When she returned, she continued drinking back at Duntroon's campus bar.

She began dancing near Hibbert, a more senior cadet whom she had a crush on.

Hibbert, she said, invited her up to his room in the Gallipoli block.

Once inside, they began having consensual sex.

But prosecutors say she asked him to stop when the sex became rough and painful.

Prosecutor Shane Drumgold said she clearly withdrew consent, repeatedly telling him to stop, but Hibbert told her he wasn't finished.

Hibbert is accused of pinning her down by her arm and her neck.

"He could obviously tell I was panicked," she said.

"All the lights were on. He was looking directly at me and he would have seen the terror in my eyes."

She allegedly told him she couldn't breathe and tried unsuccessfully to get out from under him.

But Hibbert's barrister, Philip Dunn, QC, used his cross-examination to accuse the woman of inventing a "desperate plan" to protect herself, after realising she had been seen breaking Duntroon's non-fraternisation rules, which ban male and female cadets from being alone together in rooms.

Mr Dunn accused her of lying about being choked, saying there was no medical evidence of bruising or injury around her throat or upper chest area.

He said she lied after the sex had become painful, she began to sober up, and realised that there was now little chance of an ongoing romance with Hibbert.

"You'd sold yourself cheaply," he said.

"So you knew you'd blown your chance of being a romantic interest."

The woman denied any of that was in her mind, saying she was scared and beside herself after the alleged rape.

Once she left the room, the woman said she went downstairs and sat outside before a friend came past and saw her in tears.

She said she told two friends what had happened, then a superior officer, who referred it up the hierarchy and to police.

The woman was then medically examined, and found to have bruising and sensitivity on her arm.

Mr Dunn told the jury in his opening that his client admitted having rough sex with the woman.

But the issue, he said, would be whether consent was clearly withdrawn.

"He denies that when he had sex with this young lady, in the circumstances of this night ... that he was aware she had withdrawn consent to having sexual intercourse," he said.

Mr Dunn said Hibbert conceded he had grabbed the woman's arms.

"But he denies that he did that to pin her under him to force her to have sex with him," he said.

The trial continues before Justice Richard Refshauge on Tuesday.