The first thing the creators of “The Empire Strikes Back” snow walker scene want you to know: They were not inspired by the Port of Oakland cranes.

The ever-expanding myth is frustrating, because the real story is so much better. A small group of young artists, some with almost no film experience and on a tough deadline, commit to the near-impossible task of one-upping the 1977 film “Star Wars.” And through pure talent and failure-driven ingenuity, they create one of the greatest action and special effects scenes of all time — a sequence in the 1980 sequel that still thrills more than a generation later.

“The battle of Hoth is my personal favorite not only because it’s one of the most visually stunning, but because it was a small, creative group of specialists who did the majority of the work,” says Joe Johnston, who designed the walkers and many other iconic objects in the original “Star Wars” trilogy. “There was a true sense of camaraderie and the feeling that we were pushing the frontiers.”

Read more Photo: Port of Oakland About the port cranes ... Photo: Brant Ward, The Chronicle All the key artists involved with the creation of the AT-ATs have insisted during interviews with The Chronicle that the walkers were not inspired by the Oakland port cranes. "That's a myth," said director George Lucas, when asked in 2007. "That's definitely a myth." Joe Johnston, who designed the AT-ATs, said the only major inspiration came from futurist Syd Mead's 1969 drawing "Walking Cargo Vehicle" for U.S. Steel. Photo: Lucasfilm "The urban myth about the Oakland port cranes comes from the same fantasyland that claims the Millennium Falcon was inspired by a hamburger with an olive stuck to it with a toothpick," Johnston said. "Who sticks an olive to a hamburger bun unless they're reverse engineering an urban myth?"

With the 36th anniversary of the release of “Empire” on May 21, and the walkers confirmed to return for “Rogue One: A Star Wars Story,” several key figures reflected on what sounds more like an “Ocean’s Eleven”-style heist than the seamless and well-staffed production that the finished product suggests.

‘Hilariously terrible idea’

After the exploding Death Star and medal ceremony that ended “Star Wars,” director George Lucas entered “The Empire Strikes Back” needing a huge early action sequence from his Industrial Light & Magic special effects crew. It would establish that the villainous Empire was still ruthless and dominant, surprise-attacking and destroying a rebel base.

Read more Photo: Lucasfilm They weren't always called AT-ATs Photo: Lucasfilm The name "All Terrain Armored Transport" was chosen long after the Hoth battle sequence was finished, and the name didn't show up in print reviews or articles until months after the movie was released. It's not mentioned in the movie, and most kids of that generation first saw the name in the Kenner "All Terrain Armored Transport," a holy grail "The Empire Strikes Back" toy walker from 1980 that could fit half a dozen action figures in its belly. Even in 2016, artists who worked on the scene do not call the war machines "AT-ATs." "We never referred to this design as the AT-AT," designer Joe Johnston says. "That term came much later, probably in the marketing of the toys. To the ILM crew it was always known as the Snow Walker, or usually just 'the walker.'"

“There was a long period of drawing where ‘anything goes.’ We tried wheeled vehicles, hovercraft, tank-like treaded vehicles,” Johnston says. “I personally felt that wheels and treads were too Earth-based, not exotic enough for the Empire. I remembered seeing a U.S. Steel brochure while I was in the industrial design program at Cal State Long Beach.”

It was a drawing by futurist Syd Mead, featuring what looked like a white garbage truck, walking through the snow on four insect-like appendages. Johnston expanded on the design, making the walkers seven stories tall, giving them a “head” with turrets, and a blockier body and gray paint job that matched the Empire’s Brutalist architectural look. The ILM workers called them only “the walkers”; the formal name AT-AT (All Terrain Armored Transport) was adopted by Lucasfilm merchandising long after the sequence was completed.

Adam Savage, a former ILM model shop worker and “MythBusters” star who was 14 years old when the movie came out, calls the design genius, even though a spaceship attack might have made more strategic sense.

“It’s a hilariously terrible idea for a weapon … and yet you’re totally enraptured, and it’s perfect,” Savage says. “The scale of the walkers is terrifying. The idea that you have that long period of time to watch your doom trudge toward you. The fact that they’re slightly anthropomorphized, but not too much, which is also amazing.”

As the crew got to work in ILM’s old Kerner Boulevard studio near the freeway in San Rafael, robotic walkers were considered. But Dennis Muren, who had worked on “Star Wars,” helped persuade Lucas to use the comparatively ancient art of stop-motion animation.

The biggest puppets were the size of a greyhound puppy. Ray Harryhausen, at the time almost 60 years old and the most experienced living stop-motion animator, was reportedly approached to bring them to life.

Read more Photo: Lucasfilm Making the snow walkers Photo: Tippett Studio After Joe Johnston designed the walkers, the construction of the puppets was led by armature builder Tom St. Amand, an artist who had his own machine shop. The animators also helped with the build. Tippett and Johnston said there were a few small changes from the original blueprints so they could function as puppets — the legs became chunkier for one — but Johnston's design remained mostly unchanged. The ILM workers said Lucas was supportive throughout production of the "Star Wars" movies, giving them time to experiment, and encouraged innovation. "Jon Berg, Joe Johnston and Tom St. Amand on their own volition got excited about two-legged walker," Tippett said. "So they just built it on their own on the weekends, and showed it to George. And he was like, 'Yeah, throw it in the movie.'" The two-legged All Terrain Scout Transport (AT-ST) is shown briefly in "The Empire Strikes Back" Hoth scene, then plays a key role in "Return of the Jedi." Photo: Lucasfilm

Low-tech shortcuts

Instead, Lucas ended up with a collection of long-haired artists — Tom St. Amand, Doug Beswick, Jon Berg and Phil Tippett — who could pass for a high school garage band. “I was actually surprised I got hired, because my skill level was not where it needed to be,” recalls Tippett, who was in his mid-20s when he joined the crew.

But that would be a common theme on the set, where Lucas took chances and nurtured talent. Tippett remembers 21-year-old Mike Pangrazio showing up “out of the blue,” and freehand painting the flawless matte backdrop for the frozen planet that appears in the film.

Beswick, Berg and Tippett looked like a human game of Whack-a-Mole, popping out of hatches on the volleyball-court-size set, making almost imperceptible changes to their puppets, then disappearing so the next stop-motion image could be captured on film. They wore masks, or held their breath, because the Hoth snow was actually baking soda, and a sneeze could ruin a scene.

Read more Photo: Lucasfilm The hardest sequence Photo: Lucasfilm The Hoth sequence involved a mixture of stop motion, live action, some blue screen and other, often more primitive, techniques. Tippett talks of using thin scrim of fabric called bridal tool, which dates back to 16th century theatrical productions, to give the Hoth landscape "atmospheric perspective." The day-to-day animation of the puppets was a slog; with no animation software to help, the artists had to keep track of the walker moves in their heads. But the most challenging shots may have been two scenes where the walkers crash and blow up, which were shot in real time. The FX artists worried it might not work, but it meshes seamlessly with the stop motion. Dennis Muren, a tough critic of his own work, was pleased overall with the Hoth sequence. "It just reminded me, very clearly, of what it must have been like walking in when they were doing 'King Kong,' the original (1933 movie)," Muren said. "It was all the same techniques. It was elaborate art-directed synthetic imagery. I thought the shots looked great. I was really happy with it."

Simulating the mass of the vehicles was a major challenge. To get the “performance” right, artists put chalk marks on the legs of Marine World elephants to study their movements. Sound designers Ben Burtt and Randy Thom chose booming audio cues, including a Dumpster opening and closing, to simulate moving leg joints.

And startlingly low-tech shortcuts were common. At one point, the animators added two more walkers to a scene with photo cutouts.

“The very first time you see the walkers, I think there was like five of them,” Tippett says. “There were three stop-motion puppets. For the background ones, we just took Polaroids, cut the Polaroids out and just threw them back there.”

Filming continued to the drop-dead date, with more animation to be finished, and a new production starting in the space the next day. Then Berg got the flu.

Read more Photo: Liz Hafalia, The Chronicle The sounds of the AT-AT Photo: Liz Hafalia, The Chronicle One of the biggest challenges for the builders and animators was giving the walkers a sense of mass — making puppets the size of a large cat look like building-sized vehicles. The sound team were a huge help. Lucasfilm sound designers Ben Burtt and Randy Thom, who both still work at Skywalker Sound, chose a metal shearing machine to represent the AT-AT's giant metal leg clanking on the ground. In an interview posted on the official "Star Wars" YouTube site, Burtt said that the creaking of the walkers' joints was closer to home. He recorded a dumpster that had been dropped off in front of his house. "It made this wonderful sound because it hadn't been oiled in its entire life," Burtt said. "That dumpster became a major part of the walker as well."

“I got to animate both of the walkers, all day long. It was like, ‘Open one hatch — make your moves — close it.’ ‘Open another hatch …’” Tippett says, laughing. “I couldn’t do it today.”

Muren and Johnston say they were thrilled with the finished product, but no one expected the adulation that followed, from the film’s release on May, 21, 1980, until today.

“I would put the Hoth (effects) sequence as one of the three best ever made,” Savage says. “I don’t think it’s an overstatement. It’s just such a flawless sequence. … It makes me sad that I’m not 15 years older. It’s a place that I would have loved to have been, up at Kerner Boulevard in 1979, working on these things.”

The walkers scene was frequently pointed out by critics in positive reviews of the film. T-shirts and toys are still in production 36 years later, and visual artist Banksy reportedly used a walker in one of his recent graffiti artworks.

Read more Photo: Kelly Gregor Hartlaub, Special to the Chronicle Snow walkers live on Photo: Kelly Gregor Hartlaub, Special to the Chronicle For most of the past 36 years, the snow walkers have been sold in toy stores. But their biggest merchandising impact may be with clothing, where AT-AT T-shirts have become kind of a wearable meme. Look around online, and one can find more than 25 official or bootleg snow walker T-shirts, from fairly straight-forward shirts sold by Lucasfilm and Target, to fan-made shirts playing off the vehicle's anthropomorphized look. Among our favorites: An AT-AT with a cone of shame like a dog, a silhouette of Darth Vader walking an AT-AT on a leash, and the "evolution" shirt with images that start with the snow walker on all fours and end with the AT-AT walking upright.

Later this year, the walkers will return for the next “Star Wars” movie, “Rogue One,” due out in December. In the film’s first trailer, released April 7, a walker attack in a more tropical location can be seen for exactly four seconds. ILM officials are revealing nothing else about their presence in the film, but the teaser confirms the first operational walker in a “Star Wars” feature film since “Return of the Jedi” in 1983.

The group involved with “The Empire Strikes Back” walker scene went on to win a combined 17 Academy Awards. Tippett started a Berkeley-based special effects house, Tippett Studio. Joe Johnston directed his own films, including “The Rocketeer” and “Captain America: The First Avenger,” and his design work can be seen at the virtual museum www.joejohnstonsketchbook.com.

But Muren says nearly four decades after the walkers were first conceived, the group is basically unchanged. Most are still close friends.

“We had a reunion for a bunch of these guys. I brought them together for a party about a year ago,” says Muren, now the longest-tenured employee at ILM. “Some of them I hadn’t seen in eight years, 10 years. And it was the weirdest thing: In five or 10 minutes, I was back to who I was back then, and they were back to who they were. We were all up to date. We were those same people again.”

Learning from their mistakes

Johnston says he doesn’t think the “Star Wars” original trilogy effects crew should be remembered as a well-oiled machine or a crack team with a clear road to success. They were something less than that, and also more.

“I firmly believe that the key to the success of ILM lay in the fact that we often had no idea how to solve a particular problem,” Johnston says. “On every film, in almost every sequence we had to brainstorm, invent and build solutions to new challenges. We made a lot of mistakes and shot a ton of film that no one will ever see, but we ultimately put images on the screen that helped make the trilogy a new milestone in cinema. And what better way to learn than from your mistakes?”

Peter Hartlaub is The San Francisco Chronicle’s pop culture critic. Email: phartlaub@sfchronicle.com Twitter: PeterHartlaub.

More on architects

Joe Johnston’s designs and history can be seen at www.joejohnstonsketchbook.com, and on Twitter @jjsketchbook.

Clips from Phil Tippett’s stop-motion “Mad God” project can be seen at www.Tippett.com. His augmented reality chess game “Hologrid: Monster Battle" is on Kickstarter. More projects on Twitter @PhilTippett.

Adam Savage interviews Tippett and other movie makers at www.tested.com, and on Twitter @DontTryThis.

More on Industrial Light & Magic at www.ilm.com and on Twitter @ILMVFX.