If you have never had a debilitating crush on a pop star, it might be hard to fathom the hysteria evoked by heart-throb Harry Styles.

And if you draw a blank at the mention of One Direction, it would be difficult to explain how incongruous it is to see the singer - the unofficial frontman of the mega-successful British boyband - suddenly pop up in a serious war film by Christopher Nolan, Styles' first acting role.

Nolan may be a renowned director and his film about the Dunkirk evacuation widely anticipated, but that is not why The Straits Times and other reporters at a press event are forbidden from posting pictures geotagged with the location, a private Los Angeles airfield far from the usual Hollywood circuit. The secrecy is to prevent a swarm of Styles fangirls from descending en masse.

Still, the actors, film-makers and publicists do their best to maintain the fiction that the 23-year-old English superstar is just like any other member of the ensemble cast.

Styles, for his part, seems to be taking his first movie-promotion tour rather seriously - albeit looking more like a rock star than a serious actor. He sports a gloriously over-the-top pink Elizabethan- style shirt with large ruffles at the collar and cuffs.

But the playful, flirtatious persona he is known for is greatly toned down and he dutifully toes the party line by repeatedly emphasising that he was but one member of the large cast - even though questions are disproportionately directed at him instead of co-star Fionn Whitehead who, like Styles, plays an English soldier in the war.

Asked if he was trying to make a statement by working with an esteemed film-maker such as Nolan for his first jump from music to acting, he says: "I feel lucky to be part of the ensemble and this project and I feel proud to have done my bit. It's an important story and I love what Chris has made and that was always the main focus over any personal jumps."

His admiration for the Memento (2000) and Inception (2010) director was the main reason he decided to audition for the part, says Styles, who swears his desire to act sprang from this alone and that he has not been secretly taking acting lessons all these years.

"I just heard he was making the film and as soon I heard about it, I was excited to watch it and wanted to be involved. I'm such a massive fan of his work and film-making in general."

Pressed to elaborate, he quips: "Maybe I'm just an attention- seeker."

Styles, who in September embarks on a world tour to perform his self-titled debut solo album - including two dates in Singapore, on Nov 23 and May 3 - says he did not fret about what his fans or moviegoers would think about his foray into acting. "I don't really think about it that way. I don't feel like I've ever tried to make decisions based on what the perception would be or thought, 'Oh, if I do this, it'll be a big deal,'" says the star, who has dated US pop star Taylor Swift, 27, and British TV presenter Caroline Flack, 37.

Making the movie itself was tough but rewarding, especially given "the sheer scale of it and how ambitious it was", he says. "Chris has this way of making these worlds and this visceral experience where you don't have to act that much - a lot of the acting is reacting to things happening around you."

The budding actor has had mostly positive reviews for his performance, including from Nolan. In a separate interview, the director says that despite facing some scepticism over the casting of Styles, the actor's talent and potential made him stand out from the many who auditioned and that "his past or his baggage is irrelevant".

Styles says he has not given much thought to whether he will pursue this new career, though he loved this role so much he would "absolutely do this one again".

This, despite the strenuous shoot, which entailed physically taxing scenes shot on and underwater.

"The focus on making the film good outweighed any personal discomfort," says Styles, who also never forgot that what he experienced on set "paled in comparison with anything the soldiers would've been through".

"But it made it all the more rewarding for it to be difficult. If this had been an easy movie to film, I think you would be able to tell and I don't think it would be as good."