Marcel Iures as the German commandant, Col Visser, with Farrell and Willis

Colin Farrell, who plays the title character, meanwhile, proved an equally obvious choice, having just come off Joel Schumacher’s low-budget Vietnam movie, Tigerland. He was the right age for the part, and he had the intensity - and obstinacy - needed for the role of Hart.

“Bruce brings a real intensity to the set, both as an actor and because of who he is,” says Ladd. “Colin, as the new kid on the block, had to step into that and grow from it, in terms of his acting and his character. It’s a case of life imitating art. His journey happens on the set and on the screen, and it’s fascinating to watch.”

The camp was built on a 400-acre site in Milovice, an hour or so from Prague. “The rule was, if it’s not authentic looking, there better be a good reason why not,” says set decorator Patrick Cassidy. “A very, very good reason.”

Farrell with Howard and Vicellous Shannon, who plays the camp’s only other black officer

The result certainly passed the test. “The camp is so accurate, it’s creepy,” says Nicholas Katzenbach, the original ‘Hart’, who visited the location during shooting. “I think it is important if you’re going to make a movie about any aspect of World War II to be as honest and realistic as you can: the good things and the bad things. I’m proud of what they’ve done here.”

“No matter how good a mood I was in, about 10 minutes before our car arrived in Milovice, I would start to get depressed,” remembers Willis. “I wasn’t sure why until I realised it was the camp itself, which was bleak and miserable. It made this one of the most physically demanding roles I’ve done.”

The film itself, however, is neither depressing nor bleak. And it moves in a quite different direction from most war films. Rather than start with dialogue and move gradually towards the action scenes, Hart’s War plunges straight into action - Hart’s capture and interrogation, the stunningly choreographed attack on his POW train and the forced march to Stalag Luft III - then builds up an even greater head of dramatic tension around the issues raised by imprisonment under the rules of war.

Terrence Howard as the African American officer Lt Scott with Farrell and Cole Hauser, who plays the racist Staff Sergeant Vic Bedford

And behind it all lies a coming-of-age story a million miles removed from what is usually meant by that phrase. “I’ve always believed that the war robbed me of my youth but gave me my manhood,” declares Hal Cook, who was actually imprisoned in Stalag Luft III and consulted with the film-makers on life in the camp. “I’m just a survivor. The heroes didn’t come home.”