Director Christopher Nolan knew his pitch for a film about the 1940 Dunkirk evacuation would be a tough sell.

Without a gigantic production budget, there was no way to re-create the rescuing of more than 300,000 British and Allied troops cornered by the Germans on the beaches of France during World War II.

Nolan knew the Hollywood studios able to bankroll this would hardly be rushing to make an expensive film about a chapter of history that Americans are unfamiliar with and with no American characters to boost its commercial appeal.

So the film-maker, who made his name with the Oscar-nominated psychological thriller Memento (2000), had to first pay his dues by building a relationship with Warner Bros studio and delivering hits such as The Dark Knight Batman trilogy (2005 to 2012), Insomnia (2002) and Inception (2010).

With that track record, he was able to get the studio to back Dunkirk, an ambitious historical epic which opens in Singapore tomorrow.

At a Los Angeles press day for the film, the 46-year-old Englishman tells The Straits Times: "The road to getting this made was a lot of big movies for the same studio that made a lot of money and a lot of trust that developed between us.

"So they trusted me when I brought them the story and said I think we could make it with universal appeal, by using the language of suspense and action.

"And I had a lot of trust in them that they would let me make the film the way it needed to be made."

Not that there was ever much doubt Nolan would do it his way.

Despite being one of the top- grossing directors of all time - with more than US$4.2 billion (S$5.7 billion) in box-office takings - he has always marched to the beat of his own drum, somehow managing to carry the cerebral, neo-noir sensibilities of his early movies over to more mainstream projects such as The Dark Knight franchise and Interstellar (2014), his sciencefiction blockbuster.

He does not look like your typical Tinseltown mover-and-shaker, either, despite living in Los Angeles with his wife and co-producer Emma Thomas, 48, and their four children.

Nolan, who famously eschews the use of a cellphone or e-mail, is dressed like an English university professor, donning a jacket, shirt and woollen waistcoat in defiance of the heatwave wilting the city that day.

Impressively, the director managed to convince the studio to let him cast a bunch of little-known British actors - Fionn Whitehead, Jack Lowden and pop star Harry Styles in his first acting role - as the young soldiers at the heart of the action in Dunkirk, which features three storylines taking place on land, at sea and in the air.

"I made it very clear. First, I wrote the script and was able to say, 'This is the film that I want to make.' And it wasn't a story many of them were familiar with, but upfront I said, 'Look, it's got to be unknowns in the film, they've got to be British' and that was understood going in."

The marketing department heaved a sigh of relief when Nolan later added some bigger names to the line-up.

"I think they were pretty pleased I slightly changed my mind and decided I wanted an actor with more experience to anchor each storyline.

"So we wound up with Tom Hardy, Kenneth Branagh, Mark Rylance and Cillian Murphy. These are big international stars, so I think the studio was pleased because they'd been fully prepared for a film completely with unknowns."

The film-maker also set out to tell "a survival story rather than a combat story", even though there are all the trappings of a conventional war epic, with elaborate action sequences and large-scale practical effects involving thousands of extras plus real ships and planes.

The total budget for Dunkirk has not been disclosed, although Nolan himself is reportedly earning US$20 million plus 20 per cent of the gross revenue from the film, making him the highest-paid director in Hollywood.

Using his trademark non-linear storytelling, the film employs a highly visual narrative with an evocative soundtrack and very little dialogue.

This, he explains, is designed to convey the moral ambiguities of the evacuation, which represented both a military disaster and, because of the heroism of the rescue, a triumph.

He sought to capture the ambivalence of the soldiers involved, some of whom he met in person while researching the film.

"This is very much a visual film and I wanted a very expressive face at the heart of it, and I got that with Fionn.

"What you're seeing is young men having been through a very traumatic experience and trying to process that experience.

"These guys on the ground, they had no idea what was going on or what they were part of, and there was a lot of ambiguity and uncertainty, a lot of tension between the human and the historical scale," he says.

"It's difficult to put into words, which is why you make the film and use the image rather than write an article about it. Because it makes you feel something that is true and relevant."

•Dunkirk opens in Singapore tomorrow.