Secretary of State John F. Kerry is greeted by U.S. Ambassador to Vietnam Ted Osius, center, and others, as he arrives at the Hanoi Airport on Jan. 12, 2017. (Alex Brandon/AP)

Secretary of State John F. Kerry returned to Vietnam on Thursday for his fourth and final visit as the top U.S. diplomat, his presence embodying the transformation of the two countries from enemies to partners.

Even as his nominated successor, Rex Tillerson, was answering questions at his confirmation hearing Wednesday, Kerry was already in the air for the 22-hour journey from Washington to Southeast Asia. It is the final trip overseas for the most traveled secretary of state in U.S. history. With his latest flight, he has now logged more than 1.4 million miles.

After two days in Vietnam, Kerry goes to Paris to confer with other foreign ministers on Middle East peace and to London for dinner with Foreign Secretary Boris Johnson. He will end the trip at an economic forum in Davos, Switzerland, then return to Washington with barely a day and a half left to savor what he has characterized as the job of a lifetime.

The Vietnam stop is particularly meaningful for Kerry, aides said. His fate has been linked to the country for almost 50 years, since he first arrived in 1968 as a young Navy lieutenant battling communist insurgents.

When Kerry was a U.S. senator from Massachusetts, he and Sen. John McCain (R-Ariz.), a former Navy pilot who was shot down over Hanoi and held as a prisoner of war, played a central role in normalizing relations between the United States and Vietnam.

In Vietnam at the close of his career in public office, Kerry will meet with government and ruling Communist Party officials and review the arc of the bilateral relationship in a policy speech. The capstone will be a riverboat trip in the Mekong Delta, where he captained a Swift boat patrol vessel during the Vietnam War. Aides said he will go to the spot in the river in Ca Mau province where he earned a Silver Star.

The United States has been providing aid to help maintain the health of the river so it can continue as an economic engine of the region. It is being undermined by hydroelectric dams upriver and the impact of climate change — an issue to which Kerry is expected to devote much of his post-government life.

Kerry arrived in Hanoi late Thursday, checking in at a hotel not far from the prison where McCain was held. ie is scheduled to meet Friday morning with Prime Minister Nguyen Xuan Phuc and Vice Foreign Minister Bui Thanh Son. Aides traveling with Kerry say that among the topics they will discuss are climate change, North Korea and China’s actions in the South China Sea — all issues that will fall to the new Donald Trump administration to deal with starting Jan. 20.

In a sign of the remarkable degree to which relations have changed ­between Vietnam and the United States, the secretary of the Communist Party of Ho Chi Minh City, formerly known as Saigon, will host a dinner for Kerry on Friday night. By next year, the United States plans to send Peace Corps volunteers to Vietnam for the first time.