Luke MacMaster demoted, sentenced to military detention after Holsworthy Barracks explosion

An army corporal has been demoted and sentenced to military detention after committing “a grossly stupid” act at a Sydney army barracks.

Luke MacMaster outside court on Thursday. Picture: Blake Foden

An army trainee had to be hospitalised with burns after an instructor put a box containing gunpowder on a campfire, said “surprise, watch this”, and walked off before it “went boom”.

The incident at a Sydney army barracks was partially captured on a six-second Snapchat video, which showed what a Defence Force magistrate described on Thursday as “an almighty explosion”.

The magistrate, Major General Michael Cowen KC, made that comment as he stripped Luke Thomas MacMaster of his rank and sentenced the 30-year-old to 120 days in military detention.

MacMaster, who was demoted from corporal to the rank of private, must serve 40 days of the term before the balance is suspended.

Luke MacMaster, centre, speaks to his lawyers outside the Defence Force Magistrates Court in Canberra. Picture: Blake Foden

He had earlier pleaded guilty to a charge of negligence in the performance of duty.

MacMaster entered the plea on Thursday after prosecutors elected not to proceed with the original, more serious charge of dangerous conduct with recklessness as to the consequences.

The incident occurred at Holsworthy Barracks. Picture: Sunday Telegraph

Reading from an agreed statement of facts at the Defence Force Magistrates Court in Canberra, a prosecutor outlined how MacMaster committed his offence at Holsworthy Barracks in July 2023.

He said School of Military Engineering trainees were relaxing by a campfire after finishing a day of “high explosive and demolition range serials”, which had involved gunpowder being used to simulate battle noises.

MacMaster, an instructor at the school, had been assigned the role of ammunition safety supervisor on the day.

As the trainees relaxed, he placed a cardboard box containing about 200 grams of unused gunpowder on the campfire and told them to prepare for a surprise.

Luke MacMaster is a member of the Australian Army.

Some inquisitive trainees peered into the box and, when the powder subsequently “went boom”, as Major General Cowen put it, it unleashed what the prosecutor called a “fireball”.

A scream could be heard in the short video, which Major General Cowen described as being “in glorious technicolour”.

The explosion resulted in one of the trainees suffering burns to his face, head and neck.

He ended up in the burns unit at Concord Hospital, where he stayed for three days and underwent surgery.

While he did not sustain any permanent scarring, the court heard he had “blemishes” on his face.

MacMaster was placed on restricted duties during the ensuing military police investigation.

A sign for Holsworthy Barracks, where the offence occurred. Picture: Sunday Telegraph

The court heard it was not unusual for gunpowder to be disposed of via a campfire, and that MacMaster had twice sought the approval of his boss, who is not accused of any wrongdoing, before doing so on the day in question.

However, he accepted he had acted with gross negligence by performing the disposal in proximity to trainees and failing to give them clear and concise orders in accordance with his duties.

By acting in the manner he did, prosecutors said, MacMaster turned what could have been a legitimate activity into an unjustifiable act of “tomfoolery”.

MacMaster’s defending officer, Lieutenant Commander Matthew Tyson, told the court the 30-year-old had represented Australia in gymnastics and worked as a mechanic before enlisting in 2015.

He said MacMaster had an otherwise “unblemished” record and aspired to join the special forces.

MacMaster had apologised to the trainee who was injured and taken responsibility for his offending, Lieutenant Commander Tyson added.

The prosecution and defence both said the offence did not warrant imprisonment or dismissal.

Lieutenant Commander Tyson also urged Major General Cowen not to reduce MacMaster’s rank, noting he would not be able to continue as an instructor if he was demoted.

While the defence sought a fine, Major General Cowen said that would be “woefully inadequate”.

The magistrate told MacMaster it was “extremely fortunate” nobody was more badly injured, remarking that the 30-year-old was lucky the trainee who suffered burns did not lose his eyesight.

Major General Cowen noted MacMaster had walked away from his “surprise” and minimised the risk to himself, acting in a “cavalier” fashion and failing “spectacularly” in his duty by doing nothing to alert the trainees to the “gross and obvious risk to their welfare”.

“A surprise it was,” he remarked.

In imposing a sentence of detention, Major General Cowen said he needed to send a message that safety must come first when handling “fundamentally dangerous” materials.

“Even a child would be able to appreciate the danger to other people, let alone someone who was the ammunition safety supervisor,” he said, labelling MacMaster’s act “grossly stupid”.