In the dead of night, bestselling children's author Michael Morpurgo watched horses skitter across the British countryside as gunfire opened up on both sides of the trenches.
The scene was so realistic that for a moment he forgot that it was just a re-enactment of the chaos of the First World War, a scene in the film adaptation of his children's novel War Horse.
"It was extraordinary seeing 200 German soldiers in the trench watching these horses careering up and down. I was lost in it," he says, admitting he left the set of the forthcoming Steven Spielberg movie. "I found it so depressing, so realistic. They had created this hellish battered wasteland and I just wanted to get out of there."
At 67, Morpurgo still cannot quite believe the acclaim War Horse has received since it was brought to the London stage four years ago. It was 30 years since the book was first published and at the time no one gave it more than a cursory look.
"The book was intended as an anthem to peace – a look at the universal suffering of the First World War as seen through the eyes of a horse," he says. "It was pretty much ignored when it came out, but fortunately the National Theatre picked it up and then Spielberg picked it up as well."
A special edition has just been published and Morpurgo realises there will be great excitement surrounding the film. However, whether it's a hit or a flop, he knows, as the author, he'll remain pretty anonymous.
"Do you know who wrote ET?," he says. "I don't. It's a Spielberg film."
Despite being happy in the shadows, the former Children's Laureate and ex-primary school teacher remains one of this country's most prolific children's authors. He's penned more than 120 books and won more awards than he can comfortably fit on the mantelpiece. Like many of his stories, his latest novel is set against a factual backdrop.
Shadow tells the story of an army sniffer dog in Afghanistan and the Afghan boy who befriends him, while previous books have tackled subjects such as the Israeli-Palestinian conflict through a child's eyes and a boy's struggle to survive after the 2004 Boxing Day tsunami. They are all causes close to his heart and he recently sent Prime Minister David Cameron a copy of Shadow.
"We are imprisoning children in this country and these are not people who've been through a trial process," says Morpurgo, who describes himself as a war baby, "imbued with the consequences of war".
"It's simply a convenient gathering point until we can put them on a plane. I feel enraged by that. I've had a reply and apparently he's handing it on to his minister for immigration."
Morpurgo initially wanted to be an actor – both his parents were thespians who met at Rada – and he has appeared in the stage adaptation of War Horse once, as an extra in the crowd, which fulfilled some earlier aspirations.
"I've engineered my life so that I do perform a lot," he explains, adding that he does readings of his stories at events nationwide.
When he and his wife moved to Devon in the Seventies they started Farms for City Children, a charity offering children the chance to work with animals. They now have farms in Devon, Wales and Gloucestershire – and a linked farm in Vermont – and some 75,000 inner city children have been through them. Far from slowing down, retirement now seems a world away.
"All this should have happened 30 years ago. It's all come at completely the wrong time, but better late than never, although I don't think my wife thinks so sometimes."
Shadow is published by HarperCollins, priced 12.99. A special edition of War Horse is published by Egmont, priced 12.99.
Michael Morpurgo was born in St Albans in 1943.
After studying English and French at London University, he went on to become a primary school teacher in Kent.
Sitting at a desk gives him backache, so he writes his novels in school exercise books, sitting on his bed.
His own favourite children's authors are Robert Louis Stevenson (Treasure Island), Rudyard Kipling (The Just So Stories) and Ted Hughes (The Iron Man).
In 2003, Michael Morpurgo became the third Children's Laureate and three years later, he was awarded an OBE and has picked up numerous literary awards for his 120 books.