An Australian soldier who groped a female colleague during a night of off-duty "hijinks" with other Defence Force members has been sentenced to 60 days in military detention.

Key points: Private accused seven sexually inappropriate acts during two nights off drinking

Private accused seven sexually inappropriate acts during two nights off drinking Guilty of groping female colleague but not guilty of charges arising from taking photos of her buttocks and kissing a male colleague twice

Guilty of groping female colleague but not guilty of charges arising from taking photos of her buttocks and kissing a male colleague twice Trial heard in military court and 60 day sentence to be served in a Defence Force Correctional Establishment

But the private was acquitted of two more indecency charges for showing others an image of his penis, with an Australian Defence Force magistrate finding it was not sexual in nature and followed risque "banter" in a beer garden.

The magistrate also acquitted the father of two of prejudicial conduct charges for taking photographs of the female colleague's buttocks — and showing colleagues — saying the behaviour took place on a night of "hijinks and joviality".

The trial was held this week at the Royal Australian Air Force's base at Amberley, south-west of Brisbane, giving a glimpse into how the military justice system operates.

Though access to the base is tightly controlled, Defence Force magistrate trials are generally public hearings.

The soldier had been on a military police training course when he was accused of inappropriate behaviour towards colleagues over two nights of "raucous" drinking at a pub.

There, the court heard he walked up behind a female colleague, slipped his hands between her legs and touched her genitals over her clothes.

The indecency offence carries a maximum penalty of seven years' jail.

The trial was held at the RAAF Base in Amberley, south-west of Brisbane. ( Supplied: RAAF )

Defence Force magistrate Commander Greg Sirtes said it was not "the worst of its kind" and instead sentenced the soldier to 60 days in military detention, 15 of those suspended.

He called the man's behaviour "utterly reprehensible" and unacceptable in the Defence Force or wider community.

It is understood those sent to the Defence Force Correctional Establishment at Holsworthy, in NSW, are stripped of their rank, with no phone or TV access, and are subjected to tough conditions and a strict rehabilitation regime, while under the gaze of 24/7 surveillance.

Nature of night out leads to acquittals

The private pleaded not guilty to seven charges, including acts of indecency without consent, assault, and prejudicial conduct.

Commander Sirtes said while CCTV footage had captured the man touching the woman's backside, a fellow soldier's "steadfast" eyewitness testimony gave the "missing link" — that he also touched her between the legs.

The victim told the trial her reaction to the incident was "what the f***?".

But Commander Sirtes found the soldier not guilty of the six other charges.

This included two more counts of an act of indecency without consent, for showing colleagues a photo of his penis while socialising in the beer garden.

The correctional establishment is in the Holsworthy Army Barracks, in Sydney's south-west. ( Dean Lewins: AAP )

Commander Sirtes said there was evidence the soldier had produced the photo during a "group discussion" about the size of his figure and his penis, but did not find the behaviour amounted to an indecent act.

The soldier was also charged with prejudicial conduct arising from taking photos of his female colleague's buttocks from different angles at the venue and later showing one picture to others that night.

Several members of the ADF testified they saw a photo.

The Defence Force magistrate said while the photos did tend to objectify the woman, he said it was a night of "hijinks and joviality" involving drinking, discussion of a sexual nature, and ADF members kissing.

He also pointed out that none of the group were in uniform or on duty at the time.

"There was no suggestion that defence members socialising at a civilian venue were acting in a way inherently prejudicial [to the ADF]," he said.

"It would have taken only a few additional facts to make it prejudicial [such as it happening on base], rather than a drunken night out."

Further, he said the prosecution also failed to prove that "two unwanted kisses" on a male colleague's mouth constituted assault.

'Inebriated at the time of gross violation'

During sentencing submissions, the soldier's defending officer, Lieutenant Russell Clutterbuck, argued the man should be sentenced to a period of detention rather than be removed from the Army or sent to a civilian jail, and said his client had taken steps to self-rehabilitate since the incident.

"He apologises to those concerned," Lieutenant Clutterbuck said.

Prosecuting officer Lieutenant Commander Simon Lindsay said the incident was "entirely unacceptable" and that every member of the ADF should be able to come to work, or socialise outside, in an environment "free from molestation".

"It's not the example expected of an Australian Army soldier," he said.

He also made reference of the ADF's Pathway to Change strategy, which is focused on cultural reform, and said the soldier's behaviour had flouted the Army's values of courage, respect and teamwork.

But he said the soldier had no criminal history and there was nothing to indicate that he "doesn't have good prospects".

In sentencing him, Commander Sirtes took into account the scale of the offence and the soldier's personal characteristics, as well as the need for punishment, deterrence, denunciation and rehabilitation.

He said although the man had been "highly inebriated" at the time, he was no longer in the throes of youth.

He labelled the offence a "gross violation" of a female colleague.

"The [ADF] environment depends on trust, teamwork and honour," he said.

"[The offence was] utterly reprehensible and an utter violation not tolerated in the Defence Force or anywhere."

The Department of Defence's website stated offences were tried within the military justice system when they substantially impact service discipline in the ADF.

"Otherwise, criminal offences or other illegal conduct are referred to civil authorities, such as the police," it said.

Earlier this year, the department began publishing details of upcoming hearings online, as part of a push to "make the military discipline system more open and transparent".