The outgoing US Secretary of State John Kerry has visited the place in the Mekong Delta where he was ambushed during the Vietnam War.
The former Navy lieutenant met a 70-year-old former member of the Viet Cong, who remembers the 1969 attack.
The pair warmly shook hands.
Mr Kerry, who is in Vietnam as part of his last trip before leaving office, won a medal for bravery for his actions but became an anti-war campaigner after returning home.
Mr Kerry told his former enemy, Vo Ban Tam, he was glad they were both alive.
Mr Tam, now a shrimp farmer, said he knew a man whom Mr Kerry shot and killed and remembered the plan of attack when they first spotted the US patrol boat.
The Viet Cong unit had a rocket launcher and was shooting at the US fighters to try to steer them into its range.
However, Mr Kerry took a bold move by leaping ashore to pursue his assailants, and shot dead the rocket launcher’s operator.
Mr Kerry, then aged 26, was credited with saving his crew and was awarded the US military’s Silver Star for bravery.
Mr Tam named the dead fighter as Ba Thanh and said he was 24 years old.
“He was a good soldier,” he told Mr Kerry, speaking through an interpreter.
Kerry never knew the name or age of the man he shot.
When he unsuccessfully ran for president in 2004, Mr Kerry faced critics who claimed he shot a teenager.
One aide to Mr Kerry told the Washington Post that the former military man had been searching Google Maps for the site of the ambush. On Thursday, he was said to have woken, jetlagged, in the middle of the night in his Hanoi hotel and called one of his old crew members to rack his brains.
Mr Kerry said returning to scene was weird and a little surreal.
The secretary of state is visiting Vietnam as the first stop on his last foreign trip before stepping aside when the Trump administration takes power next week.
It is his fourth visit to the country as Washington’s top diplomat.
Working under President Barack Obama, the veteran is known for taking a specific interest in improving relations between the US and Vietnam.
Mr Kerry was awarded other honours for his service in Vietnam, including three Purple Hearts for being wounded in action, but he became a prominent anti-war activist after returning to the US in 1969.
“It impressed on me the notion that you really need to analyse and understand what lies underneath the slogans,” Kerry told reporters on Saturday, according to news agency AFP.