"It was one of the most extreme things I've ever done," says the director of the grueling effort to depict the greatest rescue in British military history with unprecedented precision.

What sound does a German Stuka make when strafing British Tommies?

Christopher Nolan was pondering that very question — along with scores of others, like how much sand gets blown up when bombs land on the beach and what type of wool was used to make British army uniforms in 1940 — as he prepared, in early 2016, to shoot Dunkirk, his meticulously authentic nearly $100 million re-creation of the famous World War II rescue operation that saved 400,000 British troops from certain death. It's the most technically ambitious and obsessively historical film the British-born director, 47, who split his childhood between London and Evanston, Illinois, has attempted — even more challenging to shoot, he says, than Inception, with its building-bending dream sequences, or the truck-flipping mayhem of his Dark Knight movies. Actual vintage destroyers were hauled out of museums to make the film. Fleets of antique Spitfires were flown to the set in France. Vintage wool was sewn into replica uniforms for the 1,400 extras, perfect down to the placement of the buttonholes.

Of course, being a Nolan film, Dunkirk is also a nonlinear narrative, with a script that unfolds in three different time frames. One plotline takes place over a week (on the beach with trapped soldiers), another over a single day (in a rescue boat crossing the English Channel) and another over just one hour (inside an RAF fighter cockpit). "I wanted to try to create a real experience for the audience," explains Nolan. "I really wanted to stay in the point of view of these [soldiers] the whole way through the movie rather than having generals coming around a map explaining things. That was a big conceptual breakthrough for me."

The first breakthrough — the idea to make a movie about Dunkirk — had come to Nolan about 20 years earlier, during the mid-1990s, while on a boat trip with Emma Thomas, his soon-to-be wife and producing partner. They were sailing across the channel toward Dunkirk — the same route thousands of British fishing and pleasure ships took in May 1940 as part of a civilian operation to evacuate the bulk of the British army trapped on the French coast by advancing Nazis — when they ran into rough weather. The simple crossing ended up taking 19 harrowing hours. "It was one of the hardest things Chris and I have experienced in our lives," says Thomas. "But it really did bring home how incredible the achievement of the evacuation was."

At the time, Nolan was just getting started as a filmmaker — his breakthrough with 2000's Memento still was a few years away — and he knew he wasn't quite assured enough to tackle a war epic. "I did not feel ready for the technical challenges of realizing such biblical-scale events," he recalls.

Two decades and 10 films later, though, in 2014, while Nolan was visiting Winston Churchill's underground War Rooms (where Gary Oldman spends much of Darkest Hour, the other movie on this year's awards circuit that deals with Dunkirk), it suddenly occurred to him: Maybe he was ready now. He sat down with a stack of World War II history books, plucked out details that fascinated him — like how some trapped soldiers got so desperate, they waded into the ocean and attempted to swim the 29 miles home — and folded them into a script. Then he and Thomas pitched Warner Bros., where Nolan had made his previous seven movies. "We told them we were going to do it for real [without computer-generated effects]," says Thomas. "We told them we wanted to make a film about the evacuation that really would place the audience in the action."

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The filmmakers also told studio executives that they wanted to make the film without a lot of stars. Kenneth Branagh has a smallish role as a British officer; Mark Rylance has a slightly larger one as civilian boater; Tom Hardy plays one of the RFA pilots; and Cillian Murphy plays a shell-shocked survivor, but many of film's meatiest parts — the soldiers in the sand — were cast with rookie actors: Fionn Whitehead, singer Harry Styles and Aneurin Barnard, among others. "I wanted 18- and 19-year-olds because that's the truth of how we fight our wars," says Nolan. "I didn't want to cast 35-year-olds pretending to be 25."

Originally, Nolan thought he'd shoot the beach sequences off the coast of England, in Suffolk, but after taking a research trip with longtime production designer Nathan Crowley to the beaches in France where the actual evacuation took place, he changed his mind. They needed to shoot at Dunkirk, no matter how much French red tape was involved in securing permits (a lot). Then Nolan and Crowley went searching for as many vintage boats and planes as they could find. An old steamer from Norway was re-dressed to look British, a retired French destroyer was towed out of a museum and into the channel, while antique Spitfires were imported from a collection in Texas. "It was a big chunk of money," understates Thomas. Another big chunk went to reconstructing the mole, the half-mile-long pier where British soldiers lined up for evacuation. Only a small piece of it remained at Dunkirk, but based on original blueprints, the production was able to rebuild it to about 900 feet at a cost of $900,000.

Some parts of history had to be re-created from scratch, like that sound a Stuka fighter makes as it barrels in to strafe soldiers on the beach. Recordings of the eerie wail — made by a wind-driven siren on the belly of the fuselage — were too old and scratchy to be of much help. There were no actual Stuka sirens in any museums, or even any surviving blueprints. All they had to go on were old photographs, so sound engineer Richard King did his best to reverse-engineer the siren entirely from visuals. "I built a bunch," he recalls. "I just deduced the shape of it from photographs to figure out which would be best."

There were other technical challenges — mounting oversized Imax cameras on vintage airplane wings was more difficult than anyone anticipated — but by far the hardest part of the production was shooting the scenes on the water. "I'd done films with huge special effects and huge aerial units," says Nolan. "But I'd never done boats." Many of those sequences were shot in a giant artificial lake in the Netherlands (and one sinking scene was shot on the Warners lot), but that didn't make it much easier, especially on the actors. Whitehead spent days soaking in cold water, weighted down by his heavy (authentically vintage) wool uniform, covered in fake engine oil. "It's the same stuff they use to make Oreos," he says. "But it definitely didn't taste like Oreos."

For Nolan, the scenes with Rylance in a tiny evacuation vessel were among the most challenging of the entire production. "You're jammed on this boat with just a handful of crewmembers," he says. "It's almost like going back to independent film days, just this tiny splinter unit shooting all this stuff. And then a bomber would fly 10 feet over your head, and you'd be looking at warships in the distance, all of which we were coordinating with the ADs. It was this weird contrast between the intimacy of the performances we were getting and this massive world we were building around them. It was one of the most extreme things I've ever done."

The 68-day production wrapped in early September 2016, and Nolan and his longtime editor Lee Smith disappeared into an editing bay at Warner Bros. for several months to assemble the 54 hours of raw footage into a cut. And then another cut. And another. "There were so many permutations of this movie," says Smith. "I can't imagine how many I've got locked away. Every time you moved something, it had a very strong knock effect. You could slide it a little backward and forward in the timeline, and it was amazing what a difference it made to your emotional hit." In the fall and winter of 2016, Nolan and Smith held nearly weekly screenings of various versions of the film for select groups of friends, getting feedback. "What you're looking for," says Smith, "is not the things people think of in the first minutes but what they say a couple of days later."

What they are saying now, five months after Dunkirk's July release, is that Nolan has made the most successful World War II film ever released. It's certainly the highest-grossing, with its $525 million worldwide soaring past Saving Private Ryan ($481 million), Pearl Harbor ($449 million) and, for those who consider it a World War II movie, even Captain America: The First Avenger ($370 million), not accounting for inflation. Dunkirk also has emerged as one of this awards season's safer bets, scoring Golden Globe nominations for best drama, best director and best score as well as a place on just about every critics list, with Nolan getting more best director citations than anyone else.

"Dunkirk is just a story I grew up with," he says of the movie he first thought of making on that terrifying trip across the English Channel 20 years ago. "But after that boat trip, the tactile sense, the reality of what it must have been like to climb onto a boat and make that perilous crossing into a war zone — it stuck with me and grew over time." As far as Thomas is concerned, her husband's epic came at just the right moment: "It just seemed kind of nuts that nobody had ever made the film that we went on to make."

This story first appeared in the Jan. 4 issue of The Hollywood Reporter magazine. To receive the magazine, click here to subscribe.