An Australian Army captain who violated a male colleague with a beer bottle — in what his lawyer described as "tomfoolery gone wrong" during a work function— has been found guilty of rape.

Key points: Assault happened in the men's toilets during a work social function

Assault happened in the men's toilets during a work social function The victim says he experiences ongoing trauma and anxiety

The victim says he experiences ongoing trauma and anxiety Prosecutors say the accused has not apologised and showed "no contrition"

Rhiley Boyson, 26, is expected to be sentenced by a court martial panel in Canberra on Wednesday.

On Tuesday the court heard the assault happened in the men's toilets during a work social event last year.

Prosecutor Sarah Robin said there had been a certain amount of low-brow humour in the toilets, which spiralled out of control.

She said the victim had been on the floor trying to stop his pants being removed at the time of the incident.

Ms Robin read a statement from the victim in which he outlined the trauma and anxiety he had since suffered.

He said he carried a sense of shame for the impact it had on his young family.

The man said he had also had a great deal of difficulty because social events triggered his anxiety.

"I know this is as a result of this incident — at a work function, with my work colleagues — where I thought I was safe," his statement said.

'Momentary lapse' with lifelong consequences

Ms Robin questioned whether Boyson had shown remorse.

"There has been no contrition," she said.

"There is also no apology before you.

"A message needs to be sent to him that pranks that result in a violation of the person will not be tolerated."

But Boyson's lawyer, Flight Lieutenant Sophie Callan, told the court the actions of her client were an aberration.

"This conduct was an act of tomfoolery gone wrong," she said.

"There was no aggravating features like violence or restraint.

"This was a momentary lapse, which will have life long consequences for him."

Flight Lieutenant Callan also claimed the attack was not done for sexual gratification.

"This was an instance of momentary penetration, a few seconds long," she said.

The panel of five officers, who found Boyson guilty, will now consider what sentence it should impose.

The options include a term of imprisonment, dismissal and a financial penalty.