Then his own son was killed in combat in Afghanistan in 2010 and Kelly found the pain more scorching and paralyzing than he had ever imagined. But it also gave him an unbreakable bond with other family members of the fallen.
And so on Thursday, near the end of his speech at the unveiling of a memorial to 89 Marines and sailors from the 5th Marine Regiment killed in Afghanistan, Kelly made a personal offer of regret to the Gold Star family members in attendance — regret from someone who has suffered the same loss.
"From the bottom of my own broken heart, I'm sorry," he said.
His voice was not as strong as it had been moments earlier, when he spoke of America's enemies being possessed of "a reckless and mindless hate" and holding "extremist values that can never be reconciled with American values," and must be opposed and defeated.
Like the others killed in Afghanistan, Lt. Robert Kelly had been a volunteer to military service, his father said. Now they all join an "unbroken list of heroes" from other wars fought by the 5th Regiment.
The sadness "will never go away," Kelly told the families, but neither should the pride of knowing their loved ones answered their nation's call at a time of peril.
When the ceremony was finished, after taps and the playing of "Anchors Aweigh" and the "Marines' Hymn," family members went to the memorial to look at the names, to trace the outline of the lettering.
Patricia Segovia, whose grandson was Lance Cpl. Richard Rivera, said the ceremony provided a trace of comfort. She was one of nine family members who traveled from Oxnard for the unveiling. Rivera, 20, was killed by an Afghan soldier in August.
"We're proud to be here, to know he died a hero," said Segovia, who, like other members of the family, wore a button with a picture of a smiling Rivera.
Patty Schumacher, the mother of Lance Cpl. Victor Dew, came to the ceremony from Sacramento. When her son was killed, she was studying for a job in the pharmacy business. That ended the night in 2010 when the Marines notified her of her son's death, she said.
Now her focus is on preserving the memory of her son's unit — 3rd Battalion, 5th Marines. She worked on the "Boys of 3/5" page on Facebook and is arranging to talk to high school groups about her son and the others.
"They can't be forgotten," she said. "They just can't."
Robert Kelly was with the same battalion in 2010 when he was killed while leading a patrol. Like his father, he began as an enlisted Marine and, after graduating from college, became an officer. Father and son fought in Iraq, as did an older son, who is now a major.
John Kelly led Marines during the assault on Baghdad and Tikrit in 2003 and the battle in Fallouja in spring 2004. He later returned to Iraq as the top Marine. He's now commanding general of the Miami-based Southern Command.
After his speech, after thanks were given to civic groups from southern Orange County that helped fund the memorial, Kelly waded into the crowd. He made sure to talk to Marines from his son's battalion.
"They're all my sons and my daughters," he said.