How was Dunkirk made? 5 secrets behind the making of the biggest film of 2017

Christopher Nolan's war epic was a special cinematic event on a scale we’ve never seen before.

Dunkirk is the epic must-see movie of 2017.

Christopher Nolan’s powerful tour de force brought one of the most famous historical events of the 20th century to the big screen on a scale and with a detail never seen before.

[Dunkirk review: Nolan's movie is breathtaking]

Dunkirk

From Han Zimmer's grand and pounding score to the sweeping emotion and intimacy of the tragic and heroic stories on the French beaches, Dunkirk is an unforgettable and immersive film that reinvented what could be done with the war movie.

Dunkirk is available to buy now in the BT TV Store and rent from December 18th.

Here are five secrets of the making of the unforgettable film…

1. Every detail had to be correct – even the actors boot laces…

Dunkirk

Dunkirk was a passion project for Nolan that he had wanted to make for a number of years and he went the extra mile on every detail of the film. From the scenery and vehicles to the tiniest details like Harry Styles' boots.

"I'd put my uniform on and walked out and Chris checks me over," the popstar-turned-actor told the Daily Mail. "And he says to me: 'Your boots are laced wrong'. He explained that the British soldiers did them looped rather than criss-cross."

[Read more: Mark Rylance reveals that there were no chairs for actors on the set of Dunkirk]

2. There is a secret Michael Caine cameo…

Michael Caine is a close personal friend of Christopher Nolan and has appeared in every one of his films since Batman Begins in 2012, from The Prestige, the Dark Knight films to Interstellar and Inception. So it was a surprise when he wasn’t in the official cast for Dunkirk.

However, Nolan has since revealed there is a secret cameo from Caine at the start of the film – it’s Caine’s voice you hear giving orders to the pilots played by Tom Hardy and Jack Lowden.

"I wanted very much to squeeze him in here. It’s a bit of a nod to his character in Battle of Britain. And also, it’s Michael. He has to be in all my films, after all," Nolan told NJ.com.

[Read more: Dunkirk star praises Harry Styles acting talent]

3.The film was inspired by a boat trip on the English Channel

Nolan first decided that he wanted to make a film about the events of Dunkirk after a trip across the channel 25 years ago that went wrong.

Nolan and his wife Emma Thomas thought they were going on nice short trip across the Channel, but ended up on a nightmare 19-hour boar trip in hellish condition. It wasn’t comparable to the events of Dunkirk, but it showed Nolan that the setting and events were ideal for a movie.

4. The soundtrack is built around the sound of a watch

Dunkirk

"Very early on I sent Hans a recording that I made of a watch that I own, with a particularly insistent ticking, and we started to build the track out of that sound. And then working from that sound, we built the music as we built the picture cut,” Nolan told Business Insider.

The intense and brooding soundtrack is built using music called a 'Shepard tone'.

Nolan explained "It's an illusion where there's a continuing ascension of tone. It's a corkscrew effect. It’s always going up and up and up but it never goes outside of its range. And I wrote the ["Dunkirk"] script according to that principle. I interwove the three timelines in such a way that there's a continual feeling of intensity. Increasing intensity. So I wanted to build the music on similar mathematical principals. So there's a fusion of music and sound effects and picture that we've never been able to achieve before."

5. Nolan insisted on the real army boats and planes – no CGI

Dunkirk

Dunkirk’s marine coordinator Neil Andrea was given the incredible challenge of bringing together a entire 50-boat flotilla. Nolan didn’t want to CGI anything, so vessels were brought in from Holland, Denmark, Norway and beyond.

14 of the little ships that you see in the film were actually at Dunkirk. The main maritime hero of the film, the Moonstone, was not one of the original Dunkirk boats, but it was built in the 1930s and is a contemporary of many of those that were at the rescue.

[Read more: Harry Styles ready to quit acting after Dunkirk]

Dunkirk is available to buy in the BT TV Store now and rent from December 18th.

To buy the film, press the BT player button on your remote, scroll across to film and search now. Alternately, press the blue button and search for the film you want.

Got BT Broadband? Add BT TV >

Learn more about BT TV Store >