Director tells how getting every detail right was crucial to helping his cast understand emotions of war

Wasted youth, random violent death and the folly of armed conflict are the big themes of 1917, Sam Mendes’s orchestral symphony of a first world war film. But for the director and the team who made it alongside him, no detail was too small to consider.

“It was very important, the question of historical accuracy,” said Mendes. “We had two very fine historical advisers, Andy Robertshaw and Peter Barton, who are world renowned. And one military adviser, Paul Biddiss, who was also brilliant.”

The film, out in cinemas in January, has already won many admiring reviews and was premiered last Wednesday in front of Prince Charles and the Duchess of Cornwall at Leicester Square. Set on 6 April in northern France, after the Germans had staged a tactical retreat to the position known as the Hindenburg Line, 1917 follows a soldier’s deadly mission to help a family member. Mendes’s own mission as director was to be faithful to the experiences of the men who fought, including his own grandfather, Alfred H Mendes.

As a child the Oscar-winning director of American Beauty and Skyfall often listened to the wartime stories of his charismatic grandparent, a teenage lance corporal in 1917, and wondered at the thin line they described between luck and misfortune, life and death. One “fragment” in particular, the story of a message carried through the mist of no man’s land at dusk, has never left Mendes; it sparked the plot of his first screenplay, co-written with Krysty Wilson-Cairns.

“The film is a compression of time and place, so you take what’s important,” said Mendes. “You are not making a documentary, but you do want it to feel, in every possible detail, historically accurate.”

Mendes adds that Biddiss was vital for “hands-on” military and technical advice: “what’s in their kit bag, how to handle their weapons – this sort of stuff”. Robertshaw concentrated on getting the practical surroundings right: “What’s in the trenches, what’s in the dug-outs, what they would have imported or brought from home.”

Facebook Twitter Pinterest The actors are taught how to handle First World War weaponry.

The director describes Barton, the historian, as “more of an overall challenger”. Once a draft of the screenplay was written Mendes and Wilson-Cairns handed it over.

“I just said: ‘Pick as many holes in the script as you can.’ And he did. At great length. And it was tough actually. There were some really hard notes to factor in. But we did. And if we didn’t, there was a specific reason,” said Mendes.

While the shape of a military helmet might not be enough to make or marr a good film, for Mendes and his advisers it was imperative to replicate the uniforms shown in documentary footage and photographs. Many other dramas set in the trenches have thriftily relied upon re-purposed second world war helmets. But not on the set of 1917. Although the Brodie helmets worn in “the Great War” are no longer around in large numbers, Mendes’s troops wear accurate recreations. What is more, they differ subtly from one battalion to another, since at the time the film is set, helmet shape was changing.

“When I watched the footage back each day I tried to find any slip that I possibly could, such as undone ammunition pouches,” said Biddiss, an ex-paratrooper who ran the six-month training camp set up before filming by Mendes for those chosen to play troops. “In the first world war soldiers were taught to check their ammunition before they moved off,” said Biddiss. “Lance Corporal Schofield, played by George MacKay, is supposed to have fought in the Somme and so would have already had problems with his webbing [military belts and harnesses]. Soldiers had found it flapped open and the bullets often fell out so after the Somme it was modified and all soldiers were drilled to check their pouches. They still are today.”

The open-air action was filmed this summer on Salisbury Plain and in Bovingdon, Hertfordshire. Other scenes were filmed in Oxfordshire, Glasgow and in a Darlington river.

In February, before the long shoot in Salisbury, the film crew invited local men aged 16-35 to audition to become troops. And then Biddiss’s training camp began. MacKay, who stars in the film alongside Dean-Charles Chapman, has spoken of this training period as “an incredible process”.

“We had to make sure they were all mentally and physically fit,” said Biddiss. “We used about 800 men in all and about 500 for the Salisbury section, as well as the main cast. I wanted them all to understand the etiquette of the trenches.”

Several of those selected were asked to grow moustaches, although beards were not permitted, except for the Sikh soldiers in turbans.

“One of the first lessons I gave George and Dean was about their boots,” said Biddiss. “I told them looking after them would be as crucial for them as it had been for the soldiers.”

Clad in hobnail boots for 12-hour days, the young actors learned to act quickly when they felt the “hotspots” that would lead to blisters and which, during the war, would have gone on endanger their lives as full-blown trenchfoot.

“I also taught them not to put their fingers on the trigger of their guns. Soldiers are trained to do that only when about to fire,” said Biddiss.

Character was key to the advice required and so Biddiss suggested the nervous novice played by Chapman should continually check his bayonet as they await an order to go “over the top”.

He also said that when MacKay’s corporal is injured, it should be a glancing blow to the head rather than a shoulder wound that would quickly incapacitate any soldier.

Establishing the emotions felt by the assembled troops was also a priority for Mendes and Biddiss, even though some of them would be in shot just for a moment.

“I emphasised the fear and anger,” Biddiss said. “I can relate to that because I remember jumping out of a Chinook in the dark after I had been briefed that there were people out there who wanted to kill me.

“In fear, you breathe and taste the air differently, knowing you may die. And the anger was important because that is how soldiers feel when they realise they are in a dangerous situation.”

Facebook Twitter Pinterest The actors were also taught tactics and battlefield movement. Photograph: Paul Biddiss

The military adviser was especially happy with a scene near the close of the film when one of the young heroes runs through a long trench against the clock. It clearly shows how trenches were organised, with sergeants and platoon sergeants running things, while an officer is shown breaking down with nerves.

And what was the need for all this military training, followed by such a long rehearsal period? Well, Mendes had decided early on he wanted to make the film in a continuous shot, as if happening in real time.

“When Sam told me,” recalled Biddiss, “he said, ‘So it has got to be on the money from the word “Action”’. No pressure!”

And for Biddiss the film became more personal than expected. “I discovered while working on this that one of my uncles, Lance Corporal Robert Victor Biddiss of the London Regiment, had died in December 1917 as he moved into the Hindenburg Support advance.”

The effort to honour the story accurately was then more pertinent. “It was important for all of us to get it right, not just for Sam, because we all have relatives who fought.”