Excerpted from Variety senior features editor David S. Cohen’s “Pacific Rim: Man, Machines & Monsters — The Inner Workings of an Epic Film,” which hit bookstores June 18.

Pacific Rim” put Guillermo del Toro back in the director’s chair after five years. He was loose, free and in total control throughout a grueling but successful shoot. So why did showing footage from the movie for the first time leave him terrified?

It is Saturday at Comic-Con 2012, and the fans have overrun the San Diego Convention Center. A walk of even a few yards is an adventure, both for the difficulty of pushing through the crowd and for the Whovians and Trekkers, Sith and steampunks to be met along the way. Amid this geek tsunami, Legendary Pictures’ booth is an eddy. Fans curious about Legendary’s upcoming films besiege every entrance. A display showcasing a less familiar Legendary movie, something without a decades-long pedigree or proven fan base, can be seen through a gap in the throng.

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Behind the glass are two rugged, slightly surreal pilot suits from “Pacific Rim,” the giant-robots-vs.-giant-monsters adventure from “Hellboy” director Guillermo del Toro. No one has seen “Pacific Rim,” which is a full year away from release; the first teaser is about to be revealed nearby. The pilot suits are presented with scant explanation and there is no video of “Pacific Rim” on the booth’s video screens. Fans must make up their own minds.

And so they do. Up strides the Batman — or at least, a man in a flawless replica of the Tim Burton/Michael Keaton 1989 batsuit. He looks the suits up and down, one steampunk in olive drab, another black and glossier than his own, and renders judgment: “That’s good armor.” Then he is gone.

At an adjacent hotel, at about the same time the fans are approving his movie’s pilot suits, Guillermo del Toro is struck by a sudden attack of nerves. Such anxiety is new for del Toro; Comic-Con is family for him. His films alone make him royalty here: horror films “Cronos” and “The Devil’s Backbone”; the more mainstream “Hellboy” movies; and his 2006 masterpiece “Pan’s Labyrinth.” Moreover, he loves comicbooks, science fiction, and fantasy as much as anyone in a superhero suit, and the fans love him for it.

But this day, while he is dressing, “It hit me like a ton of bricks,” he recounts. “I grabbed my wife and I said ‘I’m absolutely petrified.’ ”

“You have a beautiful movie, don’t worry,” she said. That set him at ease — but only for a moment.

“Rarely has a movie been more important for me personally,” del Toro explains. “Not since ‘Cronos,’ or maybe ‘Pan’s Labyrinth,’ has a movie been that important.” “Pacific Rim” is del Toro’s child, and she’s about to make her debut in front of 6,500 fans in Hall H, Comic-Con’s harshest crucible.

Warner Bros. and Legendary’s presentation includes teasers for “Man of Steel” and a mood piece for a film about Godzilla. As “Pacific Rim’s” turn approaches, “Everybody around me was very happy, confident,” del Toro says. “I was shitting my pants.” He worries “Pacific Rim” could be judged harshly by the Comic-Con crowd because of the movies he hasn’t made in the four years since he made an appearance here, the most recent being an adaptation of H.P. Lovecraft’s “At the Mountains of Madness,” which was canceled at the last moment.

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The lights dim and the “Pacific Rim” teaser unspools. Del Toro watches the crowd as they get their first glimpse of the world of “Pacific Rim.” “To fight monsters … We created monsters,” the titles proclaim. There are glimpses of mortal combat between robots and monsters, striking pilots in those high-tech suits, and their leader making the stirring declaration, “We are canceling the apocalypse!”

As the trailer ends, the crowd roars.

“That was huge,” says del Toro “It was completely a life-affirming experience. I was very moved by the chitter-chatter, the hush, the whispers. I felt the room was really, really excited,” he says. “That’s what affected me in a beautiful way.”

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After the ovation, del Toro forgets “everything” — forgets his agenda, forgets to show the trailer a second time. “It’s very rarely that I get overwhelmed at a public event,” he says. “I was overwhelmed completely.”

That night he screens the footage again, more calmly this time, for a few lucky fans at a nearby hotel, taking questions from them after and hanging out with them as they munch on popcorn and hot dogs. This is the Guillermo del Toro they love: exuberant, generous, and warm. But they don’t realize that not so long before, del Toro had been in a suspended state. He needed a tonic, something to restore the pleasure of filmmaking and the wonder he’d felt as a boy watching movies in Guadalajara. He had needed a movie where he could feel creative freedom and a sense of support from partners who wanted to make the movie as badly as he did.

He found all that, and more, in “Pacific Rim.”

The director of a movie has been likened to the general of a small army. The comparison seems especially apt when the movie has huge sets, hundreds of extras, and several production tracks running simultaneously. But like a good general, an effective director is a leader, not just a commander. A director who handles people well can inspire cast and crew to perform miracles. A poor leader will find few willing to go beyond the call for the sake of the show.

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Like the desperate band of misfits fighting from the Shatterdome to save the world, the “Pacific Rim” company found themselves stretching their resources, wrestling with complex technology, and pushing themselves beyond their limits. Guillermo del Toro led them through every challenge. Yet few realized that del Toro, having decided to change his approach to running the set, was in uncharted territory himself.

“I made a life decision that this movie needed to be huge in scope but run very, very tight on the production,” he says, “and the first person to change was me.” He had never shot a movie in less than 115 days; on “Pacific Rim” he would have just 103. The only way he could finish on time was to schedule a splinter unit so he could direct it early in the day, before main unit, and on his off days. For much of the schedule, he would work 17 or 18 hours a day, seven days a week.

Del Toro also decided to take a new approach to directing actors. “If you watch ‘Pan’s Labyrinth’ or ‘The Devil’s Backbone,’ I had an obsession that was really, really all-consuming with making the actors move in an extremely mannered way that matched the camera moves,” he says. “In those movies I wanted it to be balletic, but I also wanted it to be almost like a ritual or a dance. But on ‘Pacific Rim’ I needed to allow the actors to breathe a lot more. I wanted to shoot a lot looser and even allow for improvisation, which I had never done.”

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One thing did not change about del Toro’s approach: He demands total control. “Everything, 100% goes through me sooner or later,” he says. “I do not delegate anything. Some people like it, some people don’t, but it has to be done that way.”

Del Toro’s sense of command extends to the way he calls “Action!” Most directors delegate the “Action!” call to the first assistant director, but not del Toro. (Legacy FX co-owner) Shane Mahan calls del Toro’s “Action!” shout the loudest he’s ever heard. It’s such a signature sound that crew members shout “Action!” at del Toro when they pass him on the street.

Del Toro says he also uses his “Action” command to give subtle instructions to cast and crew. “If it’s an intimate scene, I’ll go very small, or I’ll be even sometimes as polite as ‘When you want’ or ‘When you’re ready.’ But if it’s a big thing, five hundred extras and a lot of energy, I’ve got to go huge: ‘ACTION!’ ”

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“Pacific Rim” used 101 sets, most built on nine stages at Pinewood Toronto, including two of the largest shooting stages in the world. “Every set was huge,” says Stunt Coordinator Branko Racki. “Everything was a massive spectacle. It was like, ‘Wow. We’re working here today?’ You were in awe every single day.” Even the film’s found locations, the Lake Ontario beach and the Hearn power plant, had sets built on them.

Yet as vast as the sets and crowds might be, some of the most difficult days involved shooting with just a couple of actors at a time in a small space: the Conn-pods. The Conn-pod rigs appear to be under the control of the actors, but were actually controlled by Mahan and puppeteers from Legacy Effects, who followed the actors’ movements as they operated the apparatus offscreen. “We had to dress the people into the thing, take care of them, make sure things are working, jump back down, and operate the machine,” says Mahan. “The hard part was fitting the machines to the actors, making sure that they were comfortable enough to act in them and coaching them through this very difficult time.”

And difficult it was. There was no way for the actors to anticipate how demanding their days in the Conn-pod would be. Mahan remembers an actor telling him, “I thought I was going to be in a mo-cap suit on a little platform someplace. I saw this machine and these suits and thought, ‘Whoa, we’re going to do it for real.’ ”

First into the Conn-pods were Max Martini and Rob Kazinsky as the Hansens. Kazinsky says that first day was uncomfortable. The rod connecting the backs of the pilot suits to the rigs poked their backs, and the suits themselves proved heavy enough to exhaust even the fittest performer over a full day walking/pedaling on Jaeger controls that were quickly dubbed “The NordicTrack.” There were few breaks; even a bathroom break required a full hour (30 minutes to detach from the Conn-pod and get out of the suit; 30 more to dress and reattach). Del Toro could only reassure them he’d get through the day as quickly as possible.

“What surprised me was it was so completely foreign to anything I’d ever done before,” says Martini. “You stepped into this Conn-pod, and you have Guillermo off camera on a bullhorn describing what’s happening on the outside of this thing. ‘The monsters are coming at it … and they’re scratching on the outside of the Jaeger … and they’re bashing on it now!’ For me that was the most challenging thing, acting in this full-body armor, attached to this machine, and at the same time trying to visualize what’s happening on the outside of this robot.”

After the first day, feedback from Martini and Kazinsky helped the Legacy crew adjust the pilot suits, so the actors that followed them into the Conn-pods suffered somewhat less. But only somewhat, says Kazinsky, who shot a Conn-pod scene with Idris Elba later. “Idris was hallucinating by the end of that session, but I was skipping over rainbows because it was so much better than the last time.”

Cast and crew worried about how the slight Rinko Kikuchi would handle the demands of Conn-pod shooting, but co-producer Jillian Zaks says Kikuchi never complained. Kikuchi says, “I had a love-and-hate relationship with the Jaeger, the pilot suit. It was the most physically and emotionally demanding shoot of my career.” Zaks noticed Kikuchi would sometimes close her eyes during a difficult shooting day. “I asked her one day, ‘What is it that you think about when you’re in the Connpod, when you’re working through it all?’” recalls Zaks. “And she said, ‘Oh, I think about chocolate and happy things like stuffed animals.’ ”

Branko Racki was in charge of fight choreography for the Jaeger pilots, and he found the Conn-pod scenes unlike any fights he’d ever planned. “In real time, a human throwing a punch is pretty quick,” he explains. “But the robots, because their arms are so long and big, couldn’t physically throw it as fast as a human. So we had to slow down a lot of our fight movements inside the Conn-pods. That became a challenge for the actors and the stunt performers, and myself, to make that look real.”

Cast and crew alike were also plagued by rain, not in the streets of Toronto but inside the stages. Everyone got fair warning that del Toro planned to use artificial rain, but as costume designer Kate Hawley explains, “You just go, ‘Oh, there’s going to be rain.’ But it’s torrential rain we’re dealing with.” A village of pumps, reservoirs, and steam boilers sat outside the Pinewood stages to supply downpours on demand, heated to 90-odd degrees to keep drenched performers as comfortable as possible. “You think you’re safe because you’re doing an interior shot,” says Hawley, “and Guillermo would say, ‘Wet the floor down!’ You’re sort of fighting this thing inside and out.”

“If it wasn’t rain, it was dust, and if it wasn’t dust, it was rust, and if it wasn’t rust, it was glue. It was the messiest, dirtiest movie I’ve worked on,” says Hawley delightedly.

Wet, messy, and strenuous though the shoot may have been, morale never flagged. Del Toro led by example, never late, working through his breaks and on days off. “He must be half bat, because he just never seems to sleep, really,” says actor Burn Gorman. And del Toro’s command of the set and the material was never in question. “He always seems so calm,” says Gorman. “We’re all looking to him as the captain of the ship, as it were, and you just know you are in the hands of somebody who is on top of everything.”

In free moments on set, del Toro and Guillermo Navarro would nibble carrots with hot sauce. Careless souls who ventured near them at an inopportune moment might find themselves challenged to a spicy bite. Del Toro’s old friend and collaborator Ron Perlman, who arrived five months into shooting, found the director the happiest he’s ever seen him. “I was thrilled to see it,” says Perlman, “because I’ve seen him stressed out, I’ve seen him a little frustrated, but he was truly relaxed and full of a joie de vivre that was truly infectious.”

Directors can be tyrants, but del Toro eschews that style. “I don’t get angry because I’m not insecure,” he says. Having worked on crews himself, he tries to have fun with his crew. “That said, if I need to be a motherfucker that day, I can be that. That’s also needed now and then.”

But the company found him warm and funny, even when correcting people or giving notes. That is crucial, because he is so demanding. “He’s got an amazing eye,” says Hawley. “You can’t get away with much. He’s a wily bugger for that.”

Perlman, who first worked with del Toro on Cronos more than 20 years ago, says del Toro is still the same genre geek he met then, but now he is more confident directing actors. “He didn’t know how forceful he could be with the giving of directions to actors, so he was a little bit beautifully sweet. Now he’s very, very specific,” Perlman says.

Del Toro did loosen up with the actors on “Pacific Rim,” though. He let Charlie Day, who plays Newt Geisler, improvise, shooting his scenes with three cameras so Day could move where he pleased. “I didn’t want to suffocate that energy,” says del Toro.

Del Toro’s sense of fun extends to giving notes to cast as well. Gorman, who plays Dr. Hermann Gottlieb with a limp, recalls del Toro’s voice wafting over after one take, saying “Okay, Burn, that was great, but give me less ‘Planet of the Apes,’” getting a laugh from everyone, including Gorman.

Shooting ended in April 2012, one day ahead of schedule and under budget. “Incredibly, this has been the most fun, the most satisfying shoot I’ve ever had,” del Toro says. “On any movie. I would go as far as to say it’s the only shoot I’ve ever enjoyed. Ever. Completely.”

(From “Pacific Rim: Man, Machines & Monsters — The Inner Workings of an Epic Film”; by David S. Cohen; Insight Editions)