Vice President Joe Biden today delivered a deeply personal and, at times, emotional address to survivors of slain U.S. military service members, recounting his struggle with intense grief after his wife and daughter were killed in a car accident almost 40 years ago.

"For the first time in my life, I understood how someone could consciously decide to commit suicide," Biden told a Washington gathering organized by the Tragedy Assistance Program for Survivors (TAPS), a non-profit advocacy group, to commemorate Memorial Day.

"Not because they were deranged, not because they were nuts, because they'd been to the top of the mountain and they just knew in their heart they'd never get there again, that it was … never going to be that way ever again. That's how an awful lot of you feel."

Biden described how he first learned of the accident on Dec. 18, 1972, just weeks after he was first elected to the U.S. Senate from Delaware. While he was in Washington, D.C., his wife, Neilia, one-year-old daughter, Naomi, and sons, Beau and Hunter, were Christmas shopping in Hockessin, Del. Their car was struck by a tractor-trailer. Only Beau and Hunter survived.

"And just like you guys know by the tone of a phone call - you just knew, didn't you? You knew when they walked up the path. You knew when the call came. You knew. You just felt it in your bones something bad happened," Biden said. "And I knew. I don't know how I knew. But the call said my wife was dead, my daughter was dead, and I wasn't sure how my sons were going to make it."

The vice president told the families he genuinely understands the "black hole you feel in your chest, like you're being sucked back into it." And, he said, while the ache never goes away, it "gets controllable."

"Just remember two things," he said. "Keep thinking what your husband or wife would want you to do. Keep thinking what it is, and keep remembering those kids of yours, or him or her the rest of their life, blood of my blood, bone of my bone, because, folks, it can and will get better," he said.

"There will come a day, I promise you, and your parents, as well, when the thought of your son or daughter or your husband or wife brings a smile to your lips before it brings a tear to your eye," he said. "It will happen. My prayer for you is that day will come sooner or later. But the only thing I have more experience than you in is this: I'm telling you it will come."