David Ayer‘s “Fury” is a big war movie set in a tiny little space.

The tale of a World War II tank crew led by Brad Pitt also includes Shia LaBeouf, Michael Pena, Logan Lerman and Jon Bernthal. The brutal combat film deals with themes familiar from Ayer’s last movie, “End of Watch,” or his script for “Training Day”: tensions between men in tough, violent jobs.

In preparation for “End of Watch,” Ayer stuck Pena and Jake Gyllenhaal in a car together for months of LAPD ridealongs. With a bigger cast and less time for “Fury,” the director settled for a shorter but intense period of rehearsals, as well as a week-long boot camp that included sparring matches between the actors.

See photos: Angelina Jolie and Brad Pitt First Look in ‘By the Sea’

Both Pena and Bernal spent their time on recent late-night shows talking about those daily fights – so when TheWrap sat down with Ayer shortly before Friday’s release of the Sony Pictures film, that’s where we started.

TheWrap: We hear that you had your actors fight with each other during rehearsals. What was that about?

David Ayer: Mostly, it’s a great trust-building exercise and a great bonding exercise. Actors will play a lot of games with each other. It’s like magicians constantly testing tricks on each other. But there’s nothing more honest than walking into a punch.

There’s nothing like having them do some heavy sparring, and then you do a rehearsal immediately afterward. There’s just an honesty that comes from that.

Also read: ‘Fury’ Cast All Wanted Brad Pitt to Love Them on Set: ‘He Was the Father of the Tank’

Obviously yours isn’t the first movie to put actors through a mock boot camp. But when you’re dealing with movie stars who make lots of money and know they’ll be going back to their luxuries, does that really work?

Absolutely. One thing that was different is that this was run by a couple of Navy SEALs. It’s not your average movie boot camp: “Hey, let’s sleep in a tent and dig some holes!” There’s a real dark art to training, and this was engineered to break down the individual and build these guys up.

And you know, first thing, day one, all the cell phones went into a hat. Brad led the way. I mean, these guys didn’t exist. They were totally isolated, totally separate, there was no Hollywood stuff going on.

I was actually a little bit jealous, because afterwards you could feel how close they were and how bonded they were. They now had this shared experience, and I hadn’t shared it with them and was always now going to be an outsider. We did a rehearsal immediately after, and it was the best rehearsal we ever had. They crushed it at that point. That’s when I saw the movie. The movie is them – it’s the study of a family.

] A family that happens to live in a tank and kill people.

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Why a World War II tank movie?

My grandparents both served in the war, and no one ever talked about it. Pretty much everything I originally learned about World War II came from movies and TV as a kid. Those were all executed in a very similar vein, and very sort of black and white.

I tried to understand what people actually experienced, and I realized that yes, it really was a fight between good and evil. But people reverse-engineer the moral clarity of the macro into the micro, which is to say that it somehow must have been morally easy for the soldier on the ground. And it wasn’t. It was just as morally and psychologically hazardous as anything happening today in Iraq or Afghanistan. The disregard for human life, the lack of rules and the inhuman tactics were all happening at the end of the war in Germany.

See video: Brad Pitt Tries to Teach Logan Lerman The Brutal Reality of War in ‘Fury’ Clip (Video)

And often World War II movies are really about famous battles. I wanted to make a movie about an anonymous day in a forgotten corner of the war toward the end, when everyone’s just beat to heck and exhausted.

But why set that story of moral and psychological hazards in a tank?

For me, it’s all about character and relationships. And there’s no better crucible to tell the story of brothers in arms than a tank. You have these five guys in this metal vessel, nowhere to go and nowhere to escape from each other. That intimacy is what I wanted to show.

[photo: Ayer at a recent armed-forces screening at Fort Benning, GA]

War movies by nature are big and epic, but so much of what’s important here happens not in a large arena, but in a little box.

Yeah, that’s the thing. So much of the movie takes place inside the tank, so we had to build a tank set. It was one of the most complex sets that anyone had ever worked on – I kept hearing that again and again from the crew. It was on a gimbal, and the turret moved, and the cannon fed and ejected shells, and machine guns fired, light switches worked and the radio even transmitted. It was wildly complex and difficult to photograph. Whenever we had to go on that set, I would just feel my soul die a little bit.

Also read: Brad Pitt Thinks Shia LaBeouf Is ‘One of the Best Actors’ He’s Ever Seen

Your last film, “End of Watch,” wasn’t a war movie, but there were definite similarities between these two films.

It’s that brotherhood in arms. People franchised on behalf of the society to exercise force, and how that makes them separate from the society that they protect. As a director, I love to show that familial energy that develops between men who risk their lives to protect us.

Do you have interest in going outside that arena?

Oh, absolutely. I want to explore different genres, I want to do different things. I think as a filmmaker, you can start to get into been-there, done-that. And I absolutely want to test myself and learn to make different kind of movies. The more variety you have as a filmmaker, the more muscles you develop.

So do you have a David Ayer romantic comedy in you?

Absolutely. In all seriousness, I really think I do.