A military prosecutor is seeking a four-year prison sentence for a former warrant officer who led a deadly training exercise in Afghanistan.

Maj. Tony Tamburro told a sentencing hearing Wednesday that Paul Ravensdale failed to protect soldiers on a weapons range near Kandahar city three years ago.

Tamburro said the soldiers trusted their superiors and never realized they were in danger.

The defence had yet to make its sentencing submission.

Ravensdale, who is now retired, was convicted last month by a court martial of four charges, including breach of duty causing death, which carries a maximum sentence of life in prison.

He was leading a test of C-19 anti-personnel mines when one misfired, killing Cpl. Josh Baker and injuring four other soldiers.

"This is a weapon of war," Tamburro said. "It's designed to do one thing and one thing only — and that is kill."

Ravensdale was convicted for ignoring safety rules that require soldiers to be at least 100 metres behind or shielded from a C-19 mine.

"[The soldiers] had the right to assume their superiors would take care of them. Tragically, as we now know, they were in harm's way," Tamburro said.

A psychologist who testified earlier in the day said jailing Ravensdale would add to his depression and hurt his recovery from post-traumatic stress disorder.

Dr. Trudi Walsh said her patient, who has been working hard to get better, has had difficulty with crowds and strangers ever since his tours in Afghanistan.

Ravensdale was leading a test of C-19 anti-personnel mines in February 2010 when one mine misfired and sent hundreds of steel ball bearings in the wrong direction. Instead of fanning out forwards, the bearings shot backwards toward soldiers who were watching.

Walsh testified that the accident, along with the deaths of some of his friends during an earlier tour in Afghanistan, have left a mark on Ravensdale.

"He has significant difficulty trusting people," she said.

"It will take a long time, with dedicated treatment, for him to get better."

Walsh said she has worked with Ravensdale for the last two years to address his anxiety and depression. He is on medication and is learning to adapt to crowds by making excursions into shopping centres and other public areas. He also is cared for by professionals at a Winnipeg clinic who specialize in post-traumatic stress disorder.

"If he is incarcerated, he would no longer have access to that specialized treatment."

Under cross-examination, Walsh acknowledged that she has not been in a jail or prison recently and has only a "general knowledge of how things work."

Ravensdale faced the most serious charges stemming from the accident because he gave the order to fire and was also the safety officer on the weapons range that day. Days after the accident, he told a military investigator he had no idea why the mine misfired. He said the blast was much louder than it should have been and "all hell broke loose."

His lawyer told the court martial last month that Ravensdale was following a training plan that had been approved by his superiors and could not have foreseen the accident.

Two of Ravensdale's superiors have already been convicted in the wake of the accident.

Maj. Darryl Watts was demoted two ranks to lieutenant and given a severe reprimand on charges of negligence and unlawfully causing bodily harm.

Maj. Christopher Lunney was demoted one rank to captain and given a severe reprimand after pleading guilty to negligent performance of duty.