Growing up in Roxbury half a century ago, Roger Harris came to believe “that South Boston was the Klan.” It was on the front-line hell of Vietnam that Harris let go of that notion.

“I hear this voice yelling, ‘Hey Boston!,’ ” Jack Joyce recalled. “Roger heard my accent and I saw ‘BOSTON’ printed across the headband of his helmet.”

Like Harris, Jack Joyce joined the Marines straight out of high school, Southie High, that is. “I wasn’t looking at the color of his skin,” Joyce recalled, “he was a guy from home, that’s all.”

There on the front-line outposts of Con Thien and Camp Carol, the black kid from Roxbury and the white kid from Southie formed a bond that lasts to this day.

“Growing up in Boston,” Harris said, “you have this tribalism, whether it’s black or white, Catholic or Protestant. But when you got to Vietnam, the tribalism was Vietnam versus America.

“The Viet Cong didn’t give a damn which neighborhood you grew up in. If you’re wearing that uniform, they were going to kill your ass and run you outta there.”

Roger Harris is one of the vets whose story is featured in “The Vietnam War,” the riveting 18-hour PBS documentary by Ken Burns and Lynn Novick.

Harris speaks about being 17 and embracing death, “because at least that way my mother would get the $10,000 benefit and be able to buy a house. She’d be rich.”

He made it home from Vietnam to have cab drivers at Logan refuse to pick him up and to hear voices in Roxbury suggest he was a fool for going off to war.

Nevertheless, he went on to graduate college, earn both his master’s and doctorate degrees, and become one of the most innovative principals in the Boston Public Schools system.

But it did not come without a price. “When people ask me, ‘How are you sane?’ I say, ‘That’s a nice assumption you’re making.’ ” Forty years after Vietnam, Roger Harris admitted that sleep is still elusive. But the bond he and Jack Joyce formed in a distant hell has been renewed in unique ways over the years.

Their first meeting after Vietnam took place when racial trouble erupted on the steps of Hyde Park High. One of the Boston police officers who responded to the rumble was Jack Joyce, the Southie kid who gave Roger Harris his allotment of C-rations when he left the front lines. The teacher and the cop embraced and proceeded to affectionately tease each other over their respective salaries.

Their second encounter took place outside a Brighton sandwich shop. Roger Harris had gone back to Riley’s Roast Beef, hoping to exact some revenge on three white assailants who had jumped him a few days earlier.

“I thought I saw the guy,” he recalled and I was going in to confront him when I hear this booming voice say, ‘ROGER HARRIS!’ I turn around and see Jack standing there. When I told him what happened he questioned the guy, who by that time was petrified.”

Today, the Roxbury kid who went off to Vietnam years ago became the educator who has made 15 trips to China and introduced the study of Mandarin at The Renaissance School.

After 42 years as a Boston police officer, Jack Joyce retired. But when Roger Harris is asked to speak anywhere about the lessons of Vietnam, “I always call Jack to join me. When I said South Boston was the Klan years ago, that was based on ignorance and fear.

“If this Ken Burns documentary can leave one lesson, I hope it will be how ridiculous it is for us to still be caught up in this race thing.”