“It’s across this landscape that the two young men are sent to preserve the lives of 1,600 men who are to be sent to attack the Hindenberg line,” the director explained. “The movie takes place in just two hours and in one unbroken shot.”

Much of the panel was devoted to just how the illusion of one continuous shot had been achieved. Cinematographer Roger Deakins, with whom Mendes worked on the James Bond movie Skyfall (2012) and other projects, revealed that he hadn’t know that was Mendes’ intention until receiving the screenplay for the pic.

“I don’t think he told me that,” Deakins said. “I think I got the script and it was on the front page: ‘This is conceived as one continuous shot.’ And I went, ‘Really?'” the lenser went on to admit, “When I first read it, I thought, 'Is it a gimmick?' But it’s not — it’s integral to the experience.”

For Mendes, the notion of the movie taking place across one shot, and in real time, was central to the project. “I had the idea about one person carry the message, then it became two people, and then I thought, 'What if we do it over two hours and in real time?,' and then it was, 'What if this was one continuous shot?'" the filmmaker recalled. “I want to step every step with the characters. I want to breathe with them.”

Krysty Wilson-Cairns, who worked on the script with Mendes, said that she was surprised by how bold his vision for the film was.

“I remember the first call I had with Sam, and he left it to the very last bit: ‘Oh, it’s all one continuous shot.’ And I thought I played it cool, but I didn’t — I screamed,” she said, laughing, before admitting that the idea presented unique problems in terms of writing, not least of which was attempting to construct a satisfying narrative that takes place in real time across two hours. However, Wilson-Cairns added, “the fact that it was hard [to write] doesn’t matter, because I wasn’t doing the hard stuff. I wasn’t carrying a camera.”

The inspiration for the project came from Mendes’ grandfather, the director told the crowd.

“I think the first time I even understood the idea of war of any sort was when my grandfather told me about his experiences in the First World War,” Mendes said, explaining that he was 10 or 11 years old at the time. Like the characters in the movie, Mendes’ grandfather carried a message during the war, but, the director added, “it’s not a story about my grandfather, it’s not about him. George [Mackay, who plays the lead character Scofield] is not playing him. But the spirit of it, what these men went through, the sacrifices, the sense of believing in something greater than themselves, that is part of it.”

Both Mackay and Dean-Charles Chapman, who plays second lead Blake, were present during the panel and talked about the pressures of the unique format of the shoot, which required months of training and rehearsal before production began.

“It was such a joy. The physical relentlessness of it was such a pressure,” Mackay said, while Chapman revealed to the crowd’s — and Mendes’ — surprise that part of his research involved reading a book titled The Western Front Diaries, constructed from soldiers who’d fought in the trenches of World War I, including his great grandfather.

“I found that my great granddad had a diary entry in there,” Chapman said. “He was part of the cavalry and he got shot and wounded and he survived sitting out in No Man’s Land for four days. He survived and then he worked in a poppy dairy until he died. So that inspired me.”

The production was, in the words of Deakins, “an awesome challenge,” but everyone on the panel agreed that the results were more than worth it, with both Deakins and Mendes talking about the finished movie as an immersive, dreamlike experience.

“For me, it’s been the most exciting job of my career,” Mendes said. “I want people to see it en masse. I think there’s a human story that speaks to men and women alike. I’m really proud of it, and I hope people see it.”

Universal's 1917 is set to open in selected theaters Dec. 25 and go wide in January.