The battle on Omaha – multiple efforts along four-and-a-half miles of beach, further mythologised by Saving Private Ryan – now seems amusingly simplified by The Longest Day. It all comes down to Robert Mitchum and his men breaking down one small gap in a wall. But there was real-life chaos during the filming, as smoke from some 150 explosives filled the air.

Zanuck called it “the goddamndest mess I’ve ever seen in my life”. Neither the actors nor cameras could see through the smoke. “People were sitting, holding their faces in their hands,” Zanuck told biographer Mel Gussow. “Some had facial cuts where they had run into explosives. In one scene, where guys blow up in the air, that wasn’t staged. They were running blind. We stayed up all night working out non-smoke or white smoke. I got two takes that were good and decided we wouldn’t do it again. We would have killed somebody.”

The original ending was set to be a lone, solemn soldier tossing stones into the water. The Department of Defense, however, wanted something more gung-ho. Instead, the film ends with Robert Mitchum’s General Cota in a jeep. “Run me up the hill, son,” he commands.

The DoD was also unhappy with a scene of Americans shooting surrendering Germans (though Zanuck kept it in), while the Motion Picture Association of America raised concerns over the script’s “excessive amount of slaughter”. Sixty years on, it’s laughable – actors holding their chests bloodlessly and leaping to the ground. Zanuck added a final insert, too, at the request of a British advisor – a British flag being run up a pole.

Some British critics, however, were frosty. “Germans get a lot of screen time,” says Peter Lev. “More than the UK. The critics of the time did notice.” Not everyone in the US liked it, either. Eisenhower walked out just minutes into the film, unable to stomach the inaccuracies. When his wife, Mamie, told him he couldn’t leave, Ike replied: “The hell I can’t.”

Sixty years on, The Longest Day remains the definitive account of June 6, 1944 on film. “As an overview of how Operation Overlord unfolded, it’s peerless,” says Paul Woodadge. “You’d struggle to explain it any better in three hours.”

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