There is a moment while watching 1917 when you realise you have not breathed in quite some time. At least it certainly feels that way, such is there lentless, heart-stopping momentum of Sam Mendes’ epic war film about two young soldiers who venture across enemy lines to deliver a message that could save hundreds of lives.
It marks a change in genre for the British film-maker, who recently received a knighthood in the New Year honours and who is best known for James Bond movies Skyfall and Spectre and dramas such as American Beauty, and Road To Perdition.
“I had this idea of the story my grandfather told me of carrying a message,” he says as he casts his mind back.
“But the problem of the First World War in general is it’s a war of paralysis.
“It was only when I started researching it that I found this time in 1917 when the Germans retreated, and the land they were fighting over was abandoned. There seemed to be a story possible to tell of this epic journey.”
The film is movingly dedicated to the director’s grandfather, as well as the others who served in the armed forces in the Great War, which brought with it the weight of responsibility of honouring their sacrifice.
“It was not just familial responsibility but also generational,” the director says of a film that won the Best Motion Picture award at last week’s Golden Globes.
“You have a responsibility, it sounds corny, to the men who fell in the war and the generation that was lost.
“There aren’t many movies made on this scale that are not franchise movies these days and to be able to be allowed to make one about the First World War, you do feel there is a responsibility to try and get details right and to make something that feels not like a dry history lesson.
“You don’t want it to feel all distant and ‘good for you’ but something that is an experience and that is going to make the war feel vivid and like it happened yesterday.”
The war is estimated to have claimed the lives of an estimated 30,000 Irish soldiers, and among the Irish actors in an ensemble cast that also includes Benedict Cumberbatch and Colin Firth, are Andrew Scott and The Young Offenders’ Chris Walley.
A crucial part of the experience of following the journey of the two main soldiers, played by George MacKay and Dean-Charles Chapman, is the way the film is made.
It is shot as if in one long take, using clever camera work and editing to create a sense of continual motion.
“I felt it was all part of the same two hours of real time,” Mendes, 54, says, “one continuous shot. You can’t get out of it, you have to take every step with these men, whether you like it or not.
“But I was also very conscious that it shouldn’t be repetitive or monotonous or just a headlong race.
But filming in such a way was not without its problems, especially when there is so much room for human error.
“You have seven minutes of magic and then if someone trips or a lighter doesn’t work, you have to start again and none of it is usable,” he remembers with a laugh.
“We did see-saw between thinking, ‘Why are we doing this to ourselves?’ and ‘This is the only way to work’.”
But throughout the whole process, he had a crystal clear vision of how he wanted the film to look, meaning he even penned the script himself, alongside screenwriter Krysty Wilson-Cairns.
“I had not been a frustrated screenwriter, I just felt like it would be so much easier if I did it myself,” he says frankly.
"Otherwise I would have to try to explain it to someone else who then had to write it and I would then tell them it was wrong, so it just seemed like I needed to make the journey between what was in my head and what was on screen as short as possible.
“I thought it would be easier if I just sat down and did the work myself for a change, rather than make it the problem of a screenwriter.
“So I did a lot of work and got a story structure but then I sort of stalled and it was Krysty who put it into screenplay form.
“I can’t say I have been sitting there willing myself to write all these years, but having done it, I loved it and I hope I will do it again.”
But having worked with great playwrights through his distinguished theatre career, he admits he is still “a relative novice” when it comes to writing.
“You certainly become more vulnerable because you have no-one else to blame.
“You can’t say, ‘Well it’s the bloody script’, because that is my fault as well.”
Mendes is also aware that his film is an increasingly rare commodity - a big-budget, dramatic epic that is not part of a franchise.
“And I do think it’s important, I think you have a responsibility if you’re a film-maker who is interested in scale, to make a movie that needs to be seen on the big screen.
“I have made movies of all sorts of scale, big franchise movies, but I’ve also made tiny independent films.
“Some of the movies I made I would be fine about being seen on a smaller screen now, because small screens are getting better and television generally is superlative, and so when you do step up and make something for the cinema, you need to make it feel like you’re missing out if you’re not seeing it on the big screen.”