Everyone performs with conviction, but it is Cranston's mercurial Sal who, like Jack Nicholson before him, gives the film its propulsive energy. He says he could see Sal on the page. "Oh boy, it was so clear who that guy was! I so got it!" he says. "I know that guy! Who is in many cases someone you would do everything possible to avoid because he is exhausting, he consumes everything, he's self-medicated because of PTSD that he's never dealt with – this is how he deals with it – and yet he is the first who will have your back. It made me think the family they had, that military family, is not dissimilar from any family. There are members of my family I can't spend a lot of time with – but I love them, you know."

Any '70s film buff will spot the parallels here with The Last Detail, Hal Ashby's 1973 film about two Navy men taking a young offender across the United States to prison. Both films are based on novels published 30 years apart by Darryl Ponicsan. The characters match up: Cranston is playing an older version of Nicholson's brash Buddusky; Fishburne could be Otis Young's Mulhall; the crushed and drained Larry could be Randy Quaid's naive Meadows. Clearly, Linklater renamed the characters and shuffled the story because he wanted to avoid being confined by that idea. "I guess the most you can say – there's a little bit of an echo," he has said. "But it's not a sequel."

It is inevitably going to be read that way, however, given that trio of distinct characters and the frequent comparisons they make between the American experiences in Vietnam and Iraq. Linklater certainly isn't shying away from those. "I liked this because it wasn't just a diatribe about Iraq," he says. "I grew up with Vietnam: the news, the friends' older brothers who were killed in the war, returning vets. And then to see another war cycle come and go, you know…. we're in the middle of a war now. It seems to be endless: the perpetual war for perpetual peace, that's where we live."

It makes him worry, along with everything else, about men. "What is it about the male, that kind of general pack-animal attitude?" We need to think about that. "Not through the lens of heroics and sacrifice, but the tragedy of it." However much they rail against authority, Sal, Mueller and even Larry still believe in heroics, sacrifice and, above all, esprit de corps. Sal says the Marine Corps was the only religion that made sense to him; they all remember how great it felt to put on the dress uniform for the first time. There is a queasy sense that not only are they gradually returning to the fold, but that the film is going with them. "I was trying to honour their perspective," says Linklater. "It's kind of how they see the world."

James Quinton Johnson in Last Flag Flying.

Photo: Wilson Webb

Cranston remembers Vietnam with a different kind of nostalgia; where are those protesters now? "I think it's because of the smart phone. I think it's because technology has us so occupied that – wait, what, did you see this cat video?" he says. What doesn't come up on the smart phone are the coffins coming home or the villagers who burned to death in front of us on the news every night in the early '70s. "We heard the body count and we felt it. But they put a freeze on that. They don't have cameras in the Iraq war, no video cameras showing the caskets coming home. So it's almost a nice, tidy little thing – because if I don't see it, it didn't happen."

In a way, he says, war is always fought in the abstract. "The generals – who are in some safe place saying 'OK, send those soldiers in to take that! Oh well, that didn't work; 10,000 people died – have always had that mentality, which is dispassionate about individuals. They kind of have to be, which is scary.

Director Richard Linklater on the set of Last Flag Flying.

"Now is different, however, because we're all kept at that distance It's almost like they've outsourced the war," he says. "They would really love you to not know or care because it makes their job easier. But I think self-scrutiny is very important. In a democracy, obviously. We need to make people accountable."

Last Flag Flying is in cinemas April 25.