More than four decades have passed since U.S. soldiers left Vietnam. The legacy of the war for many ordinary Vietnamese is the horror of dioxin poisoning, which has affected an estimated three to four million people over the past 40 years.

Agent Orange was used by U.S. forces to kill large areas of jungle. But the herbicides did much more, causing cancers and birth defects in some of those exposed and in their children and grandchildren.

And to date, the U.S. government refuses to accept any liability for this enduring legacy of the American War.

Today, Danang is a peaceful and prosperous city, but 50 years ago this was the first sight of Vietnam for many U.S. soldiers.

Chuck and Doc, both former American soldiers, were apprehensive about coming back but found themselves welcomed. Doc now visits every year, and Chuck has moved to Vietnam. They are both regular visitors at this school, for children with disabilities caused by Agent Orange poisoning. They say they feel an obligation to help.

During the years of the war, chemical weapons were deployed in Vietnam by the United States. Defoliants were sprayed on the jungles, including Agent Orange, in total 20 million gallons.

Although these images of the victims of Napalm caused great controversy, Agent Orange was the silent, but much deadlier killer. The impact of the dioxins has affected as many as four million Vietnamese leading to cancers and terrible birth defects.

Mrs. The had no idea her son was sick, but by the age of 13 it became apparent something was very wrong. Now 41, he cannot do anything for himself and needs 24-hour care.

His sister is three years younger. Her symptoms have followed the course of her brother and she knows when she sees him, she is looking at the fate that awaits her.

Their mother wishes the U.S. government would acknowledge the damage agent orange has caused and offer some sort of help.

“I’m old, and day by day I see my son and daughter suffering from the effects. I need them to give us money so I can get someone to help look after them. Now I’m 77 years old and weak, and in the future I can’t look after them,” said Hoang Thi The, mother of victims.

That is, tragically, not a problem Chuck has had to worry about. He has seen a number of the children he has worked with suddenly pass away. It has not been easy coming back to Vietnam for Chuck, but he is dealing with the ghosts of the past. He wishes the U.S. government would do the same.