Harry Styles says being submerged underwater in 'Dunkirk' was nothing compared to what the soldiers went through during World War II.
The 23-year-old singer makes his acting debut as British troop Alex in Christopher Nolan's epic thriller, but he says it wasn't hard to act out as not being able to breathe for a few moments gives one a natural reaction of "panic".
He said: "It very naturally creates this sense of panic. It's so much that human instinct, that point of being underwater.
While you're down there filming and acting out the scene, you're also thinking, 'I cannot breathe for much longer than this' which obviously helps the situation."
One of the main things the One Direction star was asked when he auditioned for the part was whether he would find it challenging swimming for hours.
He told 'USA Today': "It was the day before I got to France (to shoot). "They were asking if I could swim. And it was a lot of swimming. It was more like, 'If we make you swim forever, will you drown?'"
Harry says watching the film made him realise just how much the 330,000 Allied troops on the British-led rescue mission in 1940, who were rescued from the clutches of the Nazis, went through - nothing compared to a few hours struggling for air underwater.
He said: "Watching the film, it puts it in context what these guys might have actually gone through.
"It was so real. And it makes it very difficult to complain about what we might have gone through for a few hours."