Mason Edwards, the Commando killed in a training accident on Tuesday, was a consummate professional soldier who had completed two tours of duty in Afghanistan and another in East Timor.

He loved his work, his unit and his comrades and was strong, gentle, caring and loving, his family said in a statement released by defence on Thursday.

Lance Corporal Edwards, 30, died when accidentally shot in a live fire training exercise in South Australia, ahead of a third deployment to Afghanistan with the Special Operations Task Group.

The circumstances of the accident are now under investigation by defence and the South Australian police.

"I want everyone to know that I love this line of work, the unit and the guys I work alongside," Lance Corporal Edwards wrote in his pre-deployment memoir, part of which defence released.

"We do what we do for many reasons. I need little more reason than this - anyone of us could have been born in this country (Afghanistan) but we are the lucky few who enjoy a lifestyle unsurpassed by anyone in the greatest country on earth (Australia).

"As a final note, I tell my family, friends and my one and only Cassie that I loved them all until the day I died. I will stay young forever and I will love them forever."

Family members said Lance Corporal Mason meant the world to them.

"He was so strong and yet the most gentle, caring, and loving man you would ever meet," they said.

"He made us laugh every time we were together and his easygoing attitude was infectious.

"Our hearts ache for Mason, and there aren't enough words to describe him as a person, and how we felt about him."

He is survived by his parents Julie and Kerrin, siblings Katie, Remie and Jared, nephew Henry and his partner Cassie.

Corporal Edwards, from Brisbane, was born in Birmingham, England, but spent most of his life in Queensland.

He attended Kelvin Grove State High School and then completed a Bachelor of Arts in Psychology at the University of Queensland.

He joined the army in January 2004 as one of the first entrants through the Special Forces Direct Recruiting Scheme.

He was posted to the army's commando battalion 4RAR, now designated 2nd Commando Regiment, subsequently deploying to East Timor in 2006 and to Afghanistan for the first time in May 2007. He returned to Afghanistan in June 2008.

Defence said that throughout his short but extremely busy career, he proved himself to be a consummate professional.

"During his tours to Afghanistan he demonstrated considerable mental toughness and physical endurance whilst deployed on combat operations," it said.

"When receiving both direct and indirect fires, Lance Corporal Edwards displayed a cool disposition and attended to his duties without hesitation."

His confident demeanour and professional approach under fire provided junior members of the section with an excellent role model on which to base their own reactions to difficult circumstances.

"In recognition of his strength of character, integrity and uncompromising work ethic, he was held in the highest regard by both commanders and peers alike," defence said.

Having displayed immense leadership potential in combat, he then took a promotion course, achieving the rare feat of being awarded student of merit and the best instructor.