Is 1917 a true story? The background and historical accuracy of the First World War epic shot in Glasgow explained

From director Sir Sam Mendes, First World War epic 1917 tells the story of two young British soldiers stationed in northern France who must deliver warning of an ambush before it's too late.

Starring a cast lined with some of Britain's most celebrated and up-and-coming actors, the new movie from the Skyfall director is sure to be the word on film fans' lips at the start of the new year.

Through long takes and clever editing the film appears as if it’s been created entirely in one shot - like 2015's Oscar-winning Birdman - and plays out in real time in an attempt to bring the audience as close to the characters as possible.

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But is it a true story? The production - shot partly in Glasgow - certainly seems authentic, but how much of 1917 is based in reality?

(Photo: eOne)

Here's everything we know:

What is 1917 about?

Sam Mendes' new film takes place in the spring of 1917, at the height of the First World War.

The film begins in deceptively tranquil fashion with Lance Corporals Blake and Schofield (Dean-Charles Chapman and George MacKay) sitting in a field.

(Photo: eOne)

All is calm. We can see the flowers and the grass. But then they begin the labyrinthine journey which lasts for the entire movie.

They walk through the maze-like trenches (which have individual names like Sauchiehall Street), passing exhausted and mud-encrusted soldiers; Blake and Schofield are being sent on a mission.

With miles of enemy territory to cross and not much time, their mission to pass a message to another company to call off the next day’s attack seems all but impossible.

If they don’t do so, two battalions and 1600 men are likely to be massacred. The “Hun” have laid a trap for them, pretending to retreat in order to lead the British on.

The mission has extra urgency for Blake because his brother is among the soldiers “going up".

Is it a true story?

1917 is something of a true story, loosely based on a tale the director's grandfather - Alfred H. Mendes, who served with the British Army during the First World War - told him as a child.

The film takes place in April of 1917 during Operation Alberich - a historically accurate German military withdrawal to stronger positions in northern France.

’The story of 1917 was inspired not only by my own family history, but also by many others," the latter day Mendes told genealogy company Ancestry, who delved into the events of the film and uncovered the military records of the director’s grandfather.

Alfred Mendes was a man of small stature, and so was chosen to be a messenger on the Western Front due to the relative nimbleness his slight frame allowed.

He was awarded the Military Medal after he volunteered for a dangerous mission to locate injured soldiers scattered across No-Mans Land during the Battle of Passchendaele.

"I hope very much that the stories of those that came before us and fought on our behalf live on in our movie,” said Sam Mendes.

1917 also has real life connections to lead actor George MacKay, whose character in the film is tasked to deliver a message deep in enemy territory.

That's a mission not too dissimilar from one MacKay’s three times great uncle, Albert Victor Baulk, undertook himself.

Albert was a signaller for the 196th Siege Battery in Sailly-au-Bois, France just a few miles from the German front lines where Operation Alberich took place

As a signaller and telephonist, Albert would have helped relay crucial communications to his unit, just like MacKay’s character.

When the Germans withdrew, Albert’s unit subsequently mobilised and attacked the enemy’s position at Arras, providing artillery fire to support attacking troops.

The war diary for his unit notes the following:

"196 SB [Siege Battery] Task – bombardment of trenches and strong points ahead of RFA [Royal Field Artillery] barrage, concluding with a creeping barrage covering advance of 4th Dragoons along SCARPE Valley."

1917 is released in UK cinemas on Friday 10 January