A government investigation is now underway into military training deaths after a string of fatal vehicle training accidents. It comes after one family put pressure on Congress and the Pentagon when their son was killed in a vehicle rollover.

Marine Corps First Lieutenant Hugh Conor McDowell, 24, was killed last May during a training exercise at Camp Pendleton in California when the light armored vehicle he was riding in rolled over and fell into an 18-foot ravine.

Asked if what happened to Conor could happen again, his parents, Susan Flanigan and Michael McDowell, said yes.

"It has," Flanigan told CBS News correspondent Chip Reid.

Five months before his accident, after other Marines in Conor's unit experienced a similar rollover, he wrote in his journal, "We got real lucky ... It's a miracle no one was killed."

"He predicted that there would be more rollovers and the next time somebody would die. He didn't know he was the one who would die," Michael McDowell said.

Conor's parents, along with his fiancee Kathleen Bourque, are now lobbying Congress and the Pentagon to improve military training procedures and equipment.

"This is an endemic problem, and every week or every month, more young people are dying in the rollovers," Michael said. "We're not trying to lower readiness or preparedness, but we've got to lower these deaths. They're devastating to families."

In 2019, at least 15 Marines and soldiers were killed in vehicle training accidents. Also, in the last five years, more than three times as many service members died in training-related incidents than in combat.

In October, after intense pressure from families, including the McDowells, the Government Accountability Office, the investigative arm of Congress, initiated a wide-ranging study of safety standards during training in both the Army and the Marines with a focus on vehicle rollovers.

"Does the fact that lives could be at stake here and lives could be saved by what you're doing give special urgency to you?" Reid asked Cary Russell, who is leading the investigation.

"It does. I think it's one of the most important things we do when we talk about human lives," Russell said.

Democratic Congressman John Garamendi from California is one of the members of the House Committee on Armed Services who called for the GAO to investigate the accidents. Asked what Congress can do while the GAO investigation is happening, Garamendi said, "Make sure the military knows that we're watching. Make sure they know that we're not just letting this go."

Garamendi also said the investigation might never have happened if it hadn't been for the persistence of the McDowell's.

"Would it have happened without them? I don't think so," he said. "When they showed up here in my office, I saw my daughter, I saw her fiance. I'm going to deal with this."

McDowell's parents and fiancee said they will keep fighting in Conor's name.

"He was our only child, so I know until the day I die, I'll always be thinking about it every day," his father said. "It will never be over and we will never give up and we will never give in."

Flanigan agreed. "We're not going to let this go for them or in Conor's memory."

The Army and Marines are cooperating with the GAO investigation. A Marine Corps spokesman said, "Our Marines are our most valuable asset, and we investigate each mishap to determine how we can best prevent similar events from occurring."

The Army said the loss of a soldier is a heartfelt concern for Army leaders at all levels.