Chuck Palazzo was one of numerous Americans in Danang over the weekend as officials from his country and from Vietnam pushed a button to mark a new step in an ongoing remediation project to clean up contaminated soil at a former military airbase used to store one of the most bitter legacies of the Vietnam War - Agent Orange.

Palazzo witnessed firsthand the planes unloading their ominous cargo when he was stationed here as a US reconnaissance marine. Sitting at a trendy cafe in downtown Danang, the 61-year-old describes the spray "like a misty cloud" that "smelled almost like rotting fruit."

"There were several missions that I was on when suddenly aircraft would just show up and would suddenly start spraying stuff. We had no idea what it was," he says. "When we were coming back through some of the same trails, the same jungles half a day or a day later all the leaves were gone," he says. "All the trees and the small saplings, they were wilting and dying. I'm wondering: if this is happening to the trees, what's happening to the people, the food source?"

In the 1960s and '70s, the US sprayed 12 million gallons of the herbicide - named for the color-coded orange band around the drums - to destroy jungle cover for the Viet Cong. Its highly toxic byproduct, dioxin, has been linked to diseases such as diabetes, heart disease and cancer. Vietnam claims at least 3 million people have birth defects caused by dioxin, 150,000 of whom are children.

Out of the frying pan …

The son of a family of first generation Italian immigrants, Palazzo grew up in a deprived area of New York - the Bronx. To escape a tough life on the streets, and a "dysfunctional" family, he signed up for combat when he was just 17. After a year at boot camp, he arrived in Danang in 1970 for 13 months of active service.

Despite joining the army with no knowledge of politics, he soon realized he had made a mistake. When the plane touched down in Vietnam, he saw caskets lined up on the runway with fellow marines killed in action.

"I don't think a day went by that I didn't say to myself, 'oh my gosh, why am I doing this?'" he says. "I finally accepted it, I had no choice."

One of the first things that struck him was the suffering of the locals. He made a promise to himself to come back "to do something positive for the Vietnamese people."

Legacy of war

When he returned to the US, Palazzo joined the anti-war movement, becoming a member of Veterans for Peace. He completed his education and starting working in software development.

But he soon started noticing fellow veterans were being stricken with mysterious health problems and some of their children born with deformities. They quickly connected this to their exposure to Agent Orange. Palazzo became a prominent campaigner for people affected by the poison.

In the 1980s he was one of tens of thousands of Vietnam veterans and their dependents to file a class action lawsuit against seven manufacturers of Agent Orange. Although the manufacturers did not admit liability, the case eventually ended in an out-of-court settlement of $180 million. The most any individual received was $2,000, Palazzo says.

Despite trying to get on with his life, Palazzo suffered terrifying flashbacks and nightmares, fear of crowds and loud noises - later recognized as post-traumatic stress disorder. The turning point came in 2001 when a friend who had served with him in Vietnam passed away.

"My best friend that I was here with, I met at boot camp and we came here together, he saved my life here, and he was shot as a result of that," he says. "He became paralyzed and was shipped out of here pretty quickly."

The man became dependent on narcotics and eventually died of an overdose. Palazzo was badly shaken.

A decades-old promise

He took a trip back to Vietnam to exorcise his demons. Despite feeling nervous about returning, he found people to be friendly and - above all - forgiving. He also met some who had been exposed to Agent Orange and whose children were suffering from devastating mental and physical disabilities.

"I kept on thinking back to what I planned to do when as a young kid to come back here to do something positive - and that's what I decided to do, to help the victims as much as I can."

In 2006 Palazzo relocated his software company to Vietnam. He settled in Danang, which had risen from the ashes to become a modern, progressive metropolis. He was driven not only by his business, but also by the promise he had made decades earlier to help the Vietnamese people.

With this in mind, Palazzo and two other Vietnam veterans who also live in the country set up the Vietnam chapter of Veterans for Peace. The group organizes tours for veterans to visit the country and help work on issues related to remnants of the war. Each participant donates $1,000 (725 euros) to the cause. This year 17 visitors took part.

Specter of Agent Orange

The US government, which has never admitted the link between Agent Orange and health problems, started cleaning up the former military airbase in Danang - identified as one of 28 dioxin hotspots in the country - in 2012. The 45,000 cubic meters of contaminated soil that has been collected at the site will now be heated at high temperatures to destroy the dioxin. Since it was launched, the costs of the remediation project have climbed to $84 million.

While Palazzo says he is in favor of the project, he believes the US government should be doing more - not least by helping people affected directly.

"It's not just about adding 10 or 20 dollars to their salary every month. It's about respite homes, social work, physical rehabilitation," he says.

Living in modern Vietnam has helped lay to rest some of his ghosts, but the veteran - who recently became a grandfather - says the specter of the war will always be with him, not only mentally but physically.

"I often say that the best day and the worst day of my life was when my daughter was born. I went through the same thing when my grandson was born. Not knowing. Because we've seen it skip generations. So it's a very frightening thing to live with."