07/30/2014 09:34 EDT | Updated 09/29/2014 05:59 EDT

Valcartier explosion that killed 6 cadets remembered

Dozens of men who survived a deadly accident at a summer cadet camp 40 years ago are hoping an inquiry will finally shed light on what happened.

Last May, the National Defence ombudsman announced he would investigate the 1974 grenade explosion that killed six boys during an cadet exercise at Valcartier, Quebec.

The men returned to Valcartier from across Canada Wednesday to commemorate the 40th anniversary of an incident they've never been able to forget.

They unveiled a plaque at the spot where a live grenade mixed in with dummies killed six boys and injured 30, most between the ages of 14 and 15.

For some, the memory is still too painful to talk about.

Glenn Souva was an 18-year-old instructor. He told CBC News that it was years before he understood the traumatic nature of what he saw that day.

“Mass confusion, people on the ground, people not knowing what was going on. There was one gentleman, one cadet saying he's got parts of a body all over him,” he recalled.

Souva said the worst part was everyone being told to keep quiet about what happened by their superiors at the base.

Another cadet instructor, Paul Wheeler, remembered his mother asking him how he was when he returned home two weeks later.

“I didn't tell her about the recurring nightmares and dreams and things, so I just nodded my head and said 'yup, I'm fine.' I think it happened to almost everybody,” he said.

It was only recently that both Wheeler and Souva were diagnosed with Post-traumatic Stress Disorder.

Because they were instructors at the time, their health care costs are covered by the military.

But costs incurred by the cadets are not.

They’re hoping that will change when the National Defence ombudsman concludes his investigation into the incident.