SHILO, Man. -- 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 Paul Ravensdale completely failed to protect soldiers while testing C-19 anti-personnel mines on a weapons range near Kandahar city three years ago.

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

"(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.

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 penalty of life in prison.

He was leading a test of the mines on Feb 12, 2010 when one misfired, sending hundreds of steel ball bearings backward instead of forward. The projectiles killed Cpl. Josh Baker and injured four other soldiers.

Ravensdale was convicted for ignoring safety rules that require soldiers to be at least 100 metres behind a C-19 mine unless they are shielded in a dugout, a vehicle or by some other barrier.

The weapons test had been planned for a week and the court martial was told earlier Ravensdale never consulted a military weapons training guide or the operating instructions for the C-19s.

"He did have plenty of time to get into that training safety manual and to run that range properly, but he failed to do so," Tamburro said.

The defence is expected to make its sentencing recommendation Thursday and might ask for no jail time. Ravensdale's psychologist testified for the defence Wednesday and said any incarceration could hurt Ravensdale's recovery from depression and post-traumatic stress disorder.

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

Walsh, who has worked with Ravensdale for the last two years, said his PTSD stems from the training accident as well as a tour in Afghanistan in 2008 when four of his friends were killed. The condition has made it hard for him to be in crowds or around strangers, she said. He is on medication and is cared for by professionals in Winnipeg who specialize in post-traumatic stress disorder.

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

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.