In late May 1940, Vic Viner was one of the 338,000 Allied troops on the beaches around the French port of Dunkirk hoping for rescue as the German Army neared and the Luftwaffe circled above.

At age 99, Viner met with Christopher Nolan, writer and director of a new movie about the evacuation, and tried to give the filmmaker some sense of what it was like to be trapped on those beaches. But, he insisted, “You can’t tell anybody what it was like. You had to have been there.”

Nolan and his collaborators certainly do their best to bring experiences like Viner’s to life for moviegoers. The film “Dunkirk” portrays a sequence of terrors: the horrible vulnerability of being prey to a swooping dive bomber; the helplessness of watching a ship list and hurry under the waves; the bitter necessity of pushing desperate men away from an overburdened lifeboat.