A scratchy prerecorded message crackled over American Armed Forces radio in Saigon 50 years ago, repeating that the temperature was “105 degrees and rising,” and then playing a 30-second excerpt from the song “White Christmas.”

It was a secret signal to begin emergency evacuation. After about 15 years of fighting, $140 billion in military spending and 58,220 American lives lost, the last American foothold in Saigon was falling. The Vietnam War was ending. Or was it?

Today, as the United States marks a half-century since that chaotic day in April 1975, veterans say the war continues to reverberate through American culture and politics, as well as their own lives. And the experience still holds pressing lessons, they add — lessons the nation seems not to have learned.

American newspapers printed images of the fall of Saigon that are still burned in the nation’s memory: crowds clambering to the rooftop of the U.S. Embassy to try to get on the last helicopters out.

“We witnessed the city dying there right in front of us,” recalled Douglas Potratz, a Marine veteran who was there. “So many people had died in Vietnam, and it was all gone.”

He was a 21-year-old sergeant in the embassy guard unit. After helping hundreds of people flee, he left with other Marines on the second-to-last flight out. “A lot of us cried,” he recalled this week about watching the city recede from the helicopter. “But a lot were too tired to do anything at all.”