Norman Morrison set fire to himself in front of the Pentagon as a protest against the Vietnam war, leaving his widow to bring up their three young children. By John-Paul Flintoff

One day in November, Norman Morrison left home with his baby daughter Emily, drove 40 miles to Washington DC, and just yards from the Pentagon, poured kerosene over himself before striking a match. The flames shot more than 10 feet into the air.

Coming home after collecting their two older children from school, his wife, Anne, had no idea what Norman, 31, had done. But as night fell, she wondered where he had taken Emily. Then the phone rang. It was a journalist. Realising she had no idea what had happened, he suggested she phone the hospital. She did, and was told that Norman had been badly burned. "Intuitively, I knew he hadn't survived," Anne remembers.

Her baby had not been harmed, the hospital staff assured her.

She asked friends to look after Ben, six, and Christina, five, and others to drive her to Washington. At the hospital, Anne collected Emily, who seemed fine, and Norman's possessions: wallet, comb, wedding ring and a Harris tweed jacket he had bought in Scotland after they married.

For the media outside, she wrote a statement: Norman had given his life to express his concern about the loss of life and suffering caused by America's military intervention in Vietnam.

Norman and Anne had grown up Presbyterian and Methodist, respectively, but become Quakers. As pacifists, they had put great effort into ending the war: praying, protesting, lobbying, withholding war taxes, writing letters to newspapers and people in power. But if Anne had known of Norman's plans, she would have done anything to stop him, she says.

The next morning, at home, she had to break the news to Ben and Christina. "I honestly did not know what I was going to say. I just prayed all the way up the steps and asked for help. I prayed for help and told them that, uh" – remembering, even 45 years later, Anne's voice breaks and she starts to sob gently as she continues – "I told them their dad had died because children were suffering in a country far away and he died to help them and to stop the war that was causing them such pain and suffering."

Many people, hearing this, find it impossible to understand what Norman did. It must have been harder still for his young children.

"We sat on the side of the bed and held each other. I told them Daddy would want them to be brave – a declaration I now regret. I know now that we should have cried our hearts out together. Because we did not, our family remained in a state of frozen grief for years. I believed I had no right to grieve and it was very difficult to be angry at someone who had just given his life for a cause, to try to stop a war."

Few people today have heard of Norman Morrison, but his act was front-page news around the world. The impact in the US was mixed. Some in the media suggested that Norman must have been insane. (Anne firmly denies that.) But many others were moved by what he had done and wrote to Anne to say so, even calling him a saint. (She denies that too.) She kept all the letters in cardboard boxes, hauling them round from one house to another, for years too afraid to look inside.

This year marks the 45th anniversary of Norman's death. After decades living with the consequences, Anne has published a memoir, Held in the Light, that is heartbreaking but also inspirationally forgiving. She talked to me about her husband and her life last week.

She lives in a remote town in western North Carolina, in a bungalow with a porch and a statue of Buddha on the patio, which came with the house when she bought it. The patio, overlooking the mountains that encircle the community, is a good place to sit and think, she says.

When Anne met Norman, nearly a decade before his death, he struck her as happy and attractive, guileless but determined. He cared deeply about people, but could be ill at ease socially, sometimes even "off-putting and perplexing in his manner", as she recalls. He was intense but had a quirky, off-hand sense of humour.

Though only five when he died, Christina has a few precious memories, such as holding his hand as she walked to school. "And laughing as he spun me round to Scottish reels." (He was proud of his Scots heritage.) "It's easy for his death to eclipse or define his life. Yet my father's life was filled with daring escapades, good work, spontaneous adventures and many moments of humour and kindness."

So how could he end it as he did? The day after his death, a letter arrived in Washington, addressed to Anne in Norman's handwriting. "Dearest Anne," it began, "please don't condemn me. For weeks, even months, I have been praying only that I be shown what I must do. This morning with no warning I was shown."

Interpreting his action to the children was desperately painful. "They found more questions to ask," Anne says. "'Wasn't there a better way? Why did Daddy have to be the one?'" One day Christina uttered the heartbreaking truth: "It didn't stop the war."

"I wondered how the people of a distant country could be more important than us. As a little girl, who wanted to feel special to her Daddy, my heart was broken, and so was Ben's," Christina says. "Life went on, but all the colours faded, and our home was strangely sad and empty. One of the things I miss most about my dad was being held by him."

Anne threw herself into peace work while trying to be a good mother and create a normal home. "It was more than I was able to do. I was present, but always partly on another wavelength."

Less than two years after Norman died, Anne married again. Her new husband was a long-standing friend, and the children were devoted to him, but they continued to suffer inwardly. Then Ben was diagnosed with cancer and was told his leg would have to be amputated. The illness went on and on. "I got in touch with my grief just enough to be angry with Norman for not being with us for this long battle." She realised she had remarried prematurely, and separated, then divorced.

Ben grew weaker, and after several years he died, aged 16. This second loss was devastating. "I wanted to die too," Anne says. "Life felt devoid of meaning." But she still wouldn't weep around the others. "Every time I took a shower, I cried. Looking back, I realise that I was crying for Norman too."

"I never saw my mother cry," says Christina. "And I followed her example."

Anne married for the third time, in 1974, to Bob Welsh – another Quaker, who had faced the prospect of prison for quitting the military reserves. They recently celebrated 36 years together. "He's been very generous, understanding and supportive. He didn't know Norman, but he respected him very much. I'm extremely grateful for his greatness of spirit."

Norman had set fire to himself 40 feet from the Pentagon office window of the wartime secretary of defence, Robert McNamara. Thirty years later, McNamara published a memoir acknowledging misgivings about the war, stirred up by Norman's act, that he was unable to speak of at the time. "I reacted to the horror of his action by bottling up my emotions, and avoided talking about them with anyone – even my family. I knew [they] shared many of Morrison's feelings about the war."

Others might have felt this served him right. Anne wrote to McNamara, thanking him for his candour and telling him what kind of person Norman was. McNamara phoned to thank her for the letter. "We had a surprisingly relaxed and candid conversation, as if we knew each other," she says. "Norman's death is a wound that we both carried."

Norman's sacrifice was well known in Vietnam. Anne had received letters of support and thanks for years. She knew the North Vietnamese government had issued a stamp with Norman's face on it, and named a street in Hanoi after "Mo Ri Xon". She had received condolences from President Ho Chi Minh, and an invitation to visit.

But she didn't take up the invitation until the late 90s, after a Vietnamese man approached her at a talk and told her that when he was little, like other Vietnamese children, he had learned by heart a poem dedicated to Norman by North Vietnam's poet laureate.

Anne flew to Vietnam in 1999, taking Christina and Emily with her – by now well into their 30s. They were stunned by the warmth of their welcome.

One day in her hotel, Anne felt exhausted and overwhelmed. "I did what I should have done 34 years before. I began to grieve deeply. I let out all the collected emotions – grief, bitterness, guilt, sadness and anger. I wailed and raged at Norman for leaving me at the age of 30 with such challenges, and for abandoning his children. I felt completely alone."

Eventually she cried herself out, and prayed. "Lord, help me, I can't carry this load any more. I can't carry this little family by myself." Then she fell asleep, and woke the next morning tired but peaceful.

They met a lot of Vietnamese people. "What people most wanted to do," Anne says, "was tell the stories of where they had been when they heard the news of Norman's sacrifice, often with tears streaming down their faces."

"As a child," Christina says, "the only thing that helped me understand my dad's death was being aware of the suffering in Vietnam. On our visit, I got to meet some of those children who told us how much my father's sacrifice meant to them. This was indescribably healing for me."

The wartime prime minister, Pham Van Dong, told them: "Your family is esteemed to the highest magnitude." Norman's "noble and great act" had touched "the most beautiful and valuable parts in humanity," he said.

"I went to Vietnam to say thank you for the kindness and love expressed to us," says Anne. "I came away with more love than I knew was possible."

Emily especially was venerated, because only she, as a baby, had witnessed her father's horrifying death.

One thing that had always haunted Anne was Norman's decision to take Emily with him to Washington. In his posthumous letter he'd mentioned Abraham, commanded by God to sacrifice his son Isaac. Could Norman have have thought, even briefly, of sacrificing his daughter?

Eyewitness reports were conflicted. Did Norman pass Emily to an unidentified woman? Place her on the ground? Anne knows only that Emily had no cuts, bruises, singes or burns.

Emily, older than her father was when he died, believes her presence beside him was crucial. "By involving me, I feel he was asking the question, 'How would you feel if this child were burned too?' People condemned him for my presence there when perhaps he wanted us to question this horrifying possibility. I believe I was there with him ultimately to be a symbol of truth and hope, treasure and horror altogether. And I am fine with my role in it."

Today Emily lives in the same village as Anne and Bob, who look after her sons once a week. Christina and her husband have moved nearby from Texas.

Others remain close but in a different way. In a corner of Anne's living room stands a sideboard she bought with Norman. It's now her family altar, created on her return from Vietnam in the style of altars there. "It holds pictures of Norman and Ben, my mother and dad, and childhood nanny, along with several objects special and sacred to me."

In Vietnam, Anne was moved and enchanted by the significance of family altars and the rituals performed there. "Physically they are no longer with us," she was told, "but spiritually they are still present, to give us love, encouragement and advice."

Held in the Light, by Anne Morrison Welsh, is published by Orbis, £12.99