‘Civil War’ is more real than you suspect

“I approached it no differently than ‘Transformers’ or anything I’m hired to choreograph knowing it’s fiction," said Mendoza, the military adviser on “Civil War" who was introduced to the project by stunt coordinator Jeff Dashnaw.

The film by writer-director Alex Garland has held strong at No. 1 at the box office for two weeks in a row. The story follows four journalists, including a combat photographer played by Kirsten Dunst, as they journey through the scarred landscape of a nation at war with itself. They’re traveling to Washington, D.C., where the president (Nick Offerman) is overseeing forces fighting various geographic factions, including one that allies California and Texas. The journalists encounter vigilante killers, building-to-building combat, nighttime firefights and a battle that engulfs the nation’s capital.

Mendoza has been coordinating scenes like these for more than a decade. He appeared with other real-life SEALs in the 2012 action movie “Act of Valor" before leaving the service in 2014 and moving behind the camera to supply tactical expertise on productions from “Lone Survivor" to “The Terminal List." Below, in an edited interview, he discusses his take on “Civil War" and his post-military career in fictional combat. (This interview contains plot spoilers.)

Alex Garland purposefully didn’t explain the causes of the fictional civil war in his movie. To do your job, did you need to know things that the audience doesn’t, such as why and where the rival military forces are fighting?

I didn’t know Alex at the time I was brought on. So, seeing how busy he was, I wasn’t going to go up to him and say, “I really need to understand why this is happening." Of course we were all curious. But we were there to do a job, and if you’re good at your job, you’re too busy to have those conversations.

It’s all make-believe, of course. But did you, as a veteran, have any hesitations about simulating a storming of the White House?

No. I was there to do these battle scenes, and like any other script, I don’t read into it. ​​It’s a story with a message, but it’s fiction.

What do you remember most about shooting that sequence?

After like six hours, when everyone’s exhausted and sweaty and wearing masks because of COVID, we reached this moment where we all have to be in concert with each other. Camera operators, the boom guy, the effects guy, our [fighters] moving around the camera, breaking weapons down. There was a point at the end where it was just like a perfect ballet. Everybody got the timing right. Alex and I looked at each other like, “That was pretty much perfect." I’m even getting goosebumps talking about it.

When you were active duty, was civil war in the U.S. something you trained for or even studied as a hypothetical scenario?

No. As a SEAL, we trained for maneuver warfare, to move within an enemy and destroy the enemy. You can apply that tactic to any situation. But we didn’t train for anything labeled as a civil war or a specific country or a group of people.

One of the final images in the movie shows the soldiers posing with the president’s corpse like a trophy. What was your reaction to that image?

I served in the military for a long time. I love my country. I know [that image] is fictional, but I don’t think anybody would want to see that. That image was chosen for that reason. It bookends the message of the story: We don’t want this to happen.

One reason you came into the industry was to help filmmakers get things right and not misportray people in the military. Is that still a big part of your job?

Yeah, always, in so many facets. In portraying a battle scene, it’s what we look like or how we talk. There’s also the postservice stuff, where you see a lot of movies or shows portraying veterans with PTSD, which has so many faces. You don’t want to be labeled or looked at as broken. I just want to share stories, whether it’s combat sequences, or re-creating something that really took place with someone who died in combat, or trying to rebrand the veteran in general, because I think there’s a lot of stereotypes out there.

You’re planning to co-direct a movie with Alex Garland called “Warfare." How did that project come about?

In that battle sequence at the end [of “Civil War"] we discovered a new kind of film grammar for how combat is portrayed. That scene caused this bigger conversation between Alex and me and some ideas to flow back and forth. One of my passions is to tell as many veteran or military stories as I can. With 20 years of warfighting, there are so many stories and lessons that need to be shared.

Write to John Jurgensen at John.Jurgensen@wsj.com