A small army of extras fires at an aquatic monster. Not shown: CGI monster.

Nothing is going as planned on the set of Atlantic Rim. Not even the set. Shooting today on the ultra-low-budget film—the eleventh day of a jam-packed fifteen-day shoot—was supposed to be at Naval Air Station Pensacola, a working base in Florida loaded with expensive-looking toys like air-traffic-control towers and T-45 Goshawk jets. As of last week, the film's cast and crew thought they had permission to use the facility for free, a huge coup. Then someone in the navy read the script and reached out to the producers: The higher-ups don't like the undisciplined way the soldiers are portrayed, they were told. Permission ungranted, a week before shooting was scheduled to start.

"It was FUBAR," says line producer Chris Ray, a tatted-up former navy photographer. So he spent his off day driving around Pensacola, finding the new set: a private helicopter airport that will stand in for at least seven locations in the film. "We try to take a little bit of money and make it look like a lot," says Ray. "If we start with something we know is gonna look bad, we don't even have a chance."

Ray is not joking about the "little bit of money." Atlantic Rim is a "mockbuster," a film that piggybacks on the name-brand recognition of a major-studio release. In this case, that bigger film is Pacific Rim, the $180 million sci-fi thriller directed by Guillermo del Toro and starring Idris Elba, Charlie Hunnam, and Charlie Day as humans using giant robo suits to battle skyscraper-sized sea monsters. Atlantic Rim has the same basic plot, except its $500,000 budget is less than the average blockbuster's catering bill. Much of that half million is spent on the lead actors—in this case, chiseled ex-Baywatcher David Chokachi, Graham Greene (best known as Kicking Bird in Dances with Wolves), and Naughty by Nature rapper Treach. The C-list roster is typical casting for a film from The Asylum, the studio that also brought us Abraham Lincoln vs. Zombies, Snakes on a Train, and Transmorphers. The Asylum didn't invent the mockbuster, but the L.A.-based B-movie factory mockbusts better than anyone else, making millions off the genre every year.

The scene being shot at the private airport this morning comes near the end of Atlantic Rim, just after the robot pilots—including Treach and Chokachi—win a decisive battle against the sea monsters. The director sets up in a clearing toward the back of the airport where four old army vehicles are rusting away. No one knows why they're here, but the trucks are a welcome bit of free set dressing. The director calls action.

"Let's get the hell out of here!" yells Graham Greene. "That knucklehead has just ordered a second nuclear strike! And where the hell is Red?!"

From top, three leads (Graham Greene, Jackie Moore, Treach) take direction; actor David Chokachi "inside" a robot; military adviser Paul Sinor gives extras a lesson.