Secretary of State John F. Kerry, riding a boat in Vietnam’s Mekong River Delta on Saturday, as he returns to the scene where his Swift boat crew was ambushed in 1969. (Pool photo by Alex Brandon/via Agence France-Presse/Getty Images)

It could have been 1969 again as Secretary of State John F. Kerry stood on the bow of the small boat chugging up the Bay Hap River on Saturday, the wind billowing his sleeves and his eyes darting left and right toward banks shrouded in dark foliage.

As a young Navy lieutenant, Kerry commanded a Swift boat along this stretch of churning brown waters in the middle of a free-fire zone. Here, he earned a Silver Star for his heroics when he leapt ashore after an ambush to pursue a fleeing Viet Cong with a grenade launcher and shot him dead.

Now, some 48 years later and with the rapid approach of sunset on a political career spanning almost four decades, Kerry was about to be yanked back to that time, and come face-to-face with a Viet Cong soldier who had taken part in the ambush.

Aides escorted Vo Ban Tam to greet Kerry on the dock, beside a row of blue tourist boats. Tam at 70 is three years younger than Kerry. He was Viet Cong in the communist stronghold of Ca Mau, one of the enemy lying in the tall grasses waiting to entrap unprotected, thin-skinned river patrol boats like Kerry’s.

Kerry, left, talks with Vo Ban Tam, 70, second from right, a former Viet Cong guerrilla who took part in the attack on Kerry’s Swift boat on Feb. 28, 1969. (Pool photo by Alex Brandon/via Associated Press)

Tam apparently had been tracked down by U.S. consulate officials and invited to meet the U.S. secretary of state he once tried to kill.

Speaking through a translator, Tam said that he had known the man whom Kerry had chased and killed in the firefight of Feb. 28, 1969.

His name was Ba Thanh, and he was 24 years old.

“He was a good soldier,” Tam told Kerry, explaining the training and skill required to handle an R-40 grenade launcher.

Up until that moment, all Kerry knew was that he had shot a Viet Cong soldier. Suddenly, the soldier took shape as a man, with a name and a set of skills that he had used against Kerry and his crew. And Kerry suddenly knew his age.

Tam, a successful shrimp and crab producer in Vietnam’s southernmost province, had in effect exonerated Kerry from one of the more stinging attacks his opponents raised when Kerry ran for president in 2004. His war record was repeatedly denigrated by political enemies who questioned whether he deserved the Silver Star, Bronze Star and three Purple Hearts he was awarded. They charged that he did nothing particularly heroic in Ca Mau and that the Viet Cong he shot was just a teenage boy.

That the Viet Cong was a man of 24, two years younger than Kerry at the time but old enough to be a credible threat, effectively negated the naysayers’ narrative.

A man waves as the boat with U.S. Secretary of State John F. Kerry aboard travels past him in the Mekong River Delta. (Pool photo by Alex Brandon/via Agence France-Presse/Getty Images)

Kerry stared hard at the man in the white ball cap standing before him, the river’s water reflecting off his sunglasses as he peppered Tam with questions and eagerly gobbled up details about a defining incident in his life. Tam told Kerry the Viet Cong could hear the Swift boats coming from 3,000 feet away, and he gently suggested the lumbering Americans never stood a chance.

“We were guerrillas,” he said. “We were never where you were shooting.”

“I’m glad we’re both alive,” Kerry told him as they shook hands, each putting two hands into the gesture.

Kerry’s encounter with Tam was the emotional peak of his two-day stop in Vietnam on ­Kerry’s final trip as secretary of state. His office in Foggy Bottom is packed and ready to be shipped to Boston.

It is doubtful the longtime senator from Massachusetts will ever run for public office again, but he will continue to work on climate change and ­environmental issues, and he is particularly concerned about the effect of rising sea levels and hydroelectric dams on the rivers in the lower Mekong Delta. When he wasn’t looking at the ­riverbank for some familiar marker from long ago, he was engrossed in conversation with a local ­scientist who said the effect of rising salinity and dams upstream brought once-in-100-year drought last year and threatened livelihoods.

Kerry says he will return to Vietnam, a country where he is treated as a returning prodigal son. Many here know Kerry and Sen. John McCain (R-Ariz.), who spent six years as a POW in Vietnam, for their work normalizing relations and helping transform enmity into friendship. Vietnamese officials regularly bestow big hugs on Kerry at the end of meetings, and civilians wait in the rain to watch him leave a restaurant. A local delegation that greeted him Saturday at the “delighted” that he has returned.

“John Kerry loves Vietnam, and Vietnam loves John Kerry,” said Ed Miller, a Vietnam ­historian at Dartmouth College with whom Kerry consulted about the trip.

But it is sometimes difficult to tell how much of the draw of Vietnam for Kerry is in the war that ended more than 40 years ago, and how much lies in its future potential as a regional economic powerhouse.

One aide described a jet-lagged Kerry arising in the middle of the night Thursday from his hotel suite in Hanoi and calling the United States to confer with one of his fellow crew members as he tried to figure out where they fought on Google Maps.

But when he drove past the site where he killed Ba Thanh, about 500 yards past a bridge and a collection of houses by a mangrove where Kerry and his men picked up troops and provisions, Kerry had an air of reserve.

“You know, it’s, I guess, weird,” he said, with a shrug. “It’s a little surreal. But it is real.”

Kerry is clearly proud of his work leading to normalization and beyond, as U.S. trade with Vietnam in the past 20 years has grown from $450 million to $45 billion.

“He thinks Vietnam is a major achievement of his political ­career,” said Tom Vallely, a ­longtime friend from Massachusetts who was involved in raising funds to build the nonprofit ­Fulbright University Vietnam in Ho Chi Minh City.

The war and the aftermath may be bookends, both in Kerry’s career and as a metaphor for the United States and Vietnam ­themselves.

“It’s a wonderful sense, that after all the horror we went through, we now like each other,” said David Thorne, Kerry’s ­boyhood friend, brother-in-law and adviser. “It’s a small miracle that we have found a way back, to reconciliation.”