War epic '1917' is more about human experience than history, says director Sam Mendes

For Sam Mendes, making 1917 - an epic set during World War 1 inspired by the stories his grandfather told him - was the most challenging experience of his career.

Mendes used techniques to make it appear as though the film is shot in one continuous take as it follows two young British soldiers, Schofield and Blake, on a crucial, dangerous mission behind enemy lines.

Their perilous journey, through trenches, across the bombed out craters of no-man's land and a devastated town, is an intense, visceral experience. The camera never leaves the men as they move forwards in a race against time.

"[My grandfather's] stories were never stories of heroism and bravery. They were stories of luck and chance. How lucky he was to be alive, stories of chance encounters, coincidences and how thin the line was that separated my grandfather, who survived, from his friends, who all died," the director said.

1917 has already won lavish critical praise and is nominated for 10 Oscars, including Best Picture.

We asked Mendes to tell us more about his experience of making the film:

The First World War shaped Europe, all the way up to Brexit. Is that something that interested you in making this film?

In [Britain] the war throws a big shadow - in some ways bigger than the Second World War. You go into any village or town and there's a memorial to the fallen, and we all wear our poppies on Remembrance Day. There's a sense of the world changing, a generation lost, the beginning of modern warfare. This is a war that starts with horses and cavalry and ends with tanks and machine guns.

Also, it's not difficult to draw a line between the generation that was fighting for a free and unified Europe and what's going on at the moment. But the film is not a history lesson, it's not political in that sense - at least it's not designed to be. By all means, draw parallels, but the film is an experience, and it's not a particularly nationalistic film. These two men happen to be British but they could have been French, Belgian, even German. It's about the human experience of war more than it is about the historical moment.

You have a family connection to the conflict. Could you tell us about that?

My grandfather fought in the First World War between 1916 and 1918. He enlisted as a 17-year-old and he never told his stories to the family until he had grandchildren, when he was in his 70s.

I think that's a pattern mirrored with people who fought in both wars - they struggled to express what they had been through in the immediate aftermath of the war, so often their own children didn't hear their stories.

When did you know that it was something you wanted to make as a film?

The problem with the First World War is that it was a war of paralysis, a war where hundreds of thousands of people lost their lives over a tiny stretch of land, so carrying a message - my grandfather's story - didn't seem to be a valid option.

It was only when I started researching it, and went to the Imperial War Museum [in London], that I found a time in the spring of 1917, a specific moment, where the Germans retreated to the Hindenberg Line and suddenly this land that the British had been fighting over was abandoned. The Germans had destroyed most of what was there, there was nothing of any lasting value, and there seemed to be a story that was possible to tell, this epic journey - I thought "Yes, I can write this ..."

At least 90% of the first-person accounts of the war are accounts of things like the Battle of the Somme, a few hundred yards of land.

One of the reasons why the First World War is not as represented in movies as the Second World War is that the nature of the war was static. When I found out there was a journey they could take, that was the moment when I started writing with enthusiasm.

It was a physical challenge for your leading actors. For the audience, too, it's immersive as you will them to survive. Was it the intention to make the film a physical experience?

I wanted to lock the audience together with the central characters and have that feeling that they can't get out. When we did a preview in New Jersey there was a particular person I was focused on. As a theatre director I'm used to sitting with an audience and learning from them while they watch. This one gentleman got lower and lower in his seat - during one scene he disappeared completely.

I wasn't intending to put the audience through that kind of agony but you could feel it, that visceral sense of being connected moment by moment, and that's to do with the one-shot aspect. You can feel time passing. When Schofield wakes up in one scene he doesn't know where he is, neither does the audience - he doesn't know how long he's been there and you don't know if he remembers where he's supposed to be. So you do cut the audience adrift on a couple of occasions, you do lose the central characters, and the character that remains is an inch away from death.

Were there times when you had to re-shoot an entire sequence because of a mistake?

You can have seven minutes of magic and then someone trips or a light doesn't work or a line is missed and you have to start again. The feeling was so great when we got it right that we wanted to do it again.

It was that combination of looking for great precision with the camera and spontaneity in front of the camera so that it wouldn't feel over-rehearsed, so that it would feel completely natural.

There are also very powerful emotional moments - when Schofield stumbles on a soldier singing in the woods. What was the inspiration for that scene?

We based that on a first-person account discovered at the Imperial War Museum about a single soldier stumbling onto music being played on a piano. The piano had been looted from a French farmhouse and the soldier describes how he realised, the moment he walked into the woods, that he hadn't heard music at all for two years. It was a Debussy nocturne and he said it was the most beautiful thing he'd ever heard. We were trying to find moments for the audience to breathe out - a moment of peace.

Is this a story that could be placed in any other time?

No, it was a moment in history with a terrible confluence of events: the beginning of contemporary warfare, with machine guns and tanks and planes, but no commensurate development in communications. You couldn't communicate with someone 20 yards away, but you could kill someone 2,000 yards away. The communication was impossible, so to have someone manually carrying a letter, that's a story that could only happen then.

What interests you most about depicting war in film?

In war humans are pushed to extremes. It's a situation human beings created themselves, in which they're stripped to their essence. Stripped of social status and class, asking what it means to be human. It's difficult to imagine that now, in a time where we're so self-obsessed. We're lucky we're born in peacetime, at least in the West. What does it mean to sacrifice yourself for something bigger than yourself, and for people you've never met?

This is a war that ended several monarchies in Europe, but you've chosen to leave the context out of 1917.

A movie like Jarhead, my first war movie, was a comment about American involvement in the Middle East, which at that point felt successful, but subsequently spiralled into chaos and disaster - it was a political film in that way. The last line of the movie says, "we're still in the desert". It was about how we never escaped, once we began.

In this film we deliberately made the choice with the generals, for example, that they're not unreasonable men. They're not posh idiots sending men to their deaths; they struggle to understand what's happening, and they make the best decisions they can, given the situation. Even MacKenzie, Benedict [Cumberbatch's] character - there was a sort of vague pressure to turn him into a Colonel Kurtz figure who'd gone rogue - but he's also lost in the fog of war. 

• Mendes won an Oscar for Best Director for his debut feature, 'American Beauty', in 2000. In 2012 he won the Bafta for Best British Film for 'Skyfall'. His other films include 'Road to Perdition', ' Jarhead', 'Revolutionary Road', 'Away We Go' and ' Spectre'.