The former boyband superstar makes his big screen debut in the harrowing action blockbuster.
The new trailer shows the hardship and losses faced by the British Armed Forces during the Second World War.
Nolan's movie focusses on the historic days around the evacuation of Allied troops from Dunkirk in 1940 as the German armies advanced across Europe.
After writing or directing movies like Interstellar, Inception and The Dark Knight, Dunkirk marks the British director's ambitious first project based on real events.
WBDunkirk trailer with Harry Styles
WBDunkirk trailer shows Tom Hardy as an RAF pilot
Styles may seem an unorthodox choice for such a serious and prestigious undertaking.
Nolan explained his decision: “When we put the cast together, we had some established names: Kenneth Branagh, Mark Rylance, Tom Hardy, Cillian Murphy.
"But for the guys on the beach, we really wanted young unknowns. [Styles is] not that unknown, but he’d never done anything as an actor before."
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Nolan revealed that the pop star did not receive any preferential treatment while casting the movie.
The director said: "He (Styles) auditioned. I auditioned literally thousands of young men with different combinations of young men. And he had it.”
The new trailer is a chance for his fans to see their idol after tickets for Harry Styles' intimate gigs sold out in seconds this week.
The young star is shaping his solo career on two fronts. Styles hinted he had been in the running to play Han Solo in the upcoming Star Wars spin-off.
WBDunkirk trailer with Tom Hardy
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Seventy-two years ago today saw the allied invasion of Normandy during World War II. To mark the occasion, we've put together a collection of archived photos from that historic day.
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Reinforcements disembarking from a landing barge at Normandy during the Allied Invasion of France on D-Day.
Dunkirk focusses on the terrible reality of the Allied soldiers trapped on the French beaches with nowhere left to retreat.
It also shows the bravery of ordinary people who answered the call for maritime vessels, however small, to make the crossing from the British coast and help the evacuation. Mark Rylance plays one such man, unable to enlist, but making his own invaluable contribution to the war effort.
Dunkirk also features Tom Hardy as a Royal Air Force pilot, protecting the sky over the flotilla as it makes its desperate escape back across the Channel.
Dunkirk is out in UK cinemas on July 21
The last look at the blockbuster, which tells the story of the chaotic rescue of Allied soldiers from France early in the Second World War, opens with a voiceover saying: “What has happened is a colossal military disaster. We shall go unto the end, we shall never surrender.”
It includes aerial bombardments, sinking ships, and a beach filled with ravaged troops. German planes flying overhead bomb and machine-gun ships and soldiers on the beach below.
One Direction fans will be disappointed the trailer focuses mainly on newcomer Fionn Whitehead, who plays a soldier seeking refuge on an aid ship before it is struck by a torpedo.
The brief glimpses of Harry show him on a beach with Whitehead and in the water after the attack.
Also featured in the footage are Sir Kenneth Branagh and Cillian Murphy.
It concludes with the voiceover quoting wartime prime minister Winston Churchill’s famous speech, saying: “We shall fight on the beaches, we shall fight on the landing grounds, we shall never surrender.”
Dunkirk is released in the UK on July 21.