Cpl. Josh Baker, 24, died more than two years ago when a Claymore anti-personnel mine packed with 700 steel balls raked a Canadian Forces platoon.
Cpl. Tyson Edworthy was just metres away when he realized something had gone wrong.
"I was going toward Sgt. (Mark) McKay. He began hopping and swearing and said he got hit by something," Edworthy testified at the Calgary court martial of Calgary soldier Maj. Darryl Watts.
Edworthy said he saw Baker falling down and went to help.
"He was having difficulty breathing. Blood was coming out of his mouth a bit," Edworthy said.
"He had a hole in his left chest the size of a dime. I put my hand over it."
Edworthy, who had advanced training in first aid, helped a medic attend to Baker and put decompression needles into his chest to try to help him breathe.
But it wasn't long before "we both knew Cpl. Baker wasn't alive any more."
The prosecution alleges Watts allowed his men to practise with the C19 Claymore without proper training and with "wanton, reckless disregard" even if he wasn't the range safety officer.
"Maj. Watts was the officer in command. He was the platoon commander," said senior prosecutor Maj. Tony Tamburro.
"He was not properly appointed as an officer in charge of practice, but nonetheless he was the platoon commander ... when they conducted the range and he's responsible for everything that happens."
Watts, 44, was the officer in charge the day of the accident and is charged with manslaughter, unlawfully causing bodily harm, breach of duty and negligent performance of duty.
Testimony from a number of witnesses has indicated that the range safety officer, Warrant Officer Paul Ravensdale, warned soldiers about the dangers of the Claymore and the need to stay behind armoured vehicles and away from the line of fire.
Sgt. Sam Newhook was taking video when the fatal blast erupted. He said he felt a piece of debris hit his shoulder.
"I started seeing that people were actually hurt," he said. "I realized people had been hit by the ball bearings. It wasn't just debris."
Newhook and several other soldiers, including Watts, weren't behind cover when test firings took place.
Newhook, who now is himself responsible for training soldiers on the C19, said he stresses the dangers of the anti-personnel mine.
"I make sure they know the danger areas. I seem to have a vested interest in that now."
Watts's lawyer, Balfour Der, said it's not always possible to do everything by the book in the theatre of war. He suggested the soldiers couldn't have been worried since so many of them didn't appear to heed warnings from the range safety officer.
"The evidence seems to show now that they were all told where they should be to be out of the danger zone, but many of them didn't abide by that," said Der. "I think that is the product of the fact that no one believed that this weapon was going to malfunction and fire its payload backward."
Tamburro said whether the mine malfunctioned is something that will remain a mystery.
The court martial is expected to last several weeks.
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