This article originally appeared on Den of Geek UK.
Their introduction almost matches Darth Vader’s grand entrance in the original Star Wars when it comes to sheer menace. We see the walkers first as black dots against the planet Hoth’s snow-white horizon. Then we see their huge, lumbering feet through a Rebel’s Electrobinoculars. Cut to a reaction shot of R2-D2 in the underground Rebel base, whistling fractiously as chunks of ice are shaken loose by the thud-thud of those metal feet.
It’s only after a squadron of snowspeeders is scrambled that we finally get a proper look at the Imperial walkers: looming some 15 metres above the ice, they’re a startling amalgam of tank and beast: heads bristling with cannon and blasters, armoured body mounted atop four striding legs. Compared to the Empire’s rank-and-file Stormtroopers, these monstrosities are a real force to be reckoned with.
Like so many of the best designs in the Star Wars universe, the Imperial walkers, or AT-ATs as they later became known, artfully tread the line between the fantastical and the mechanically convincing. Spindly legs may be an odd design choice for an attack vehicle, yet these hulking war machines bear all the sense of weight and wear and tear of a real-world tank or troop carrier. When the AT-ATs first strode across the world’s cinema screens in 1980’s The Empire Strikes Back, audiences had never seen anything quite like them before – little wonder, then, that they soon became one of the most recognizable designs in the Star Wars canon. (Kenner’s toy AT-AT, released to coincide with the film, quickly became an unattainably expensive holy grail for young fans of the series.)
The notion of a four-legged armored transporter may have been parodied since (an injured AT-AT holding its knee in a Family Guy special and so on), yet its design comes from some real-world research projects from the earlier part of the 20th century.
As far back as the 1930s, inventors in Italy were working on a contraption dubbed the Iron Dobbin – a “mechanical horse that trots and gallops on steel piped legs under the impulse of a gasoline engine.” According to an article at The Atlantic, the Iron Dobbin was intended to teach members of the Italian Fascist Youth Movement how to ride a horse.
The invention was soon dismissed, probably because the risk of getting a limb caught among all those spindly legs was actually more dangerous than old-fashioned horse riding. The article continues that the German military also considered developing the idea for its mountain troops, though this idea was also nipped in the bud.
The concept of a four-legged vehicle was revived in the 1960s, when General Electric began work on a tractor-like machine which could walk on four legs – the idea being that it could tackle the kind of uneven, muddy terrain that might foil a conventional tank.
As you can see in the YouTube video below, the General Electric Walking Truck, as it was dubbed, had to be operated by a complicated system of levers connected to the driver’s arms and legs. In fact, its operation isn’t unlike the monster-fighting mecha in Guillermo del Toro’s Pacific Rim:
Designed by Ralph Mosher, the Walking Truck, also known as the Cybernetic Anthropomorphous Machine, the 12-foot-tall machine would have been used to carry heavy loads across awkward terrain, though even its designer admitted that operating the truck soon became exhausting and, like the Iron Dobbin, the Walking Truck was eventually scrapped.
When it came to pushing the boundaries of engineering, Mosher was something of a pioneer. From the ’50s onwards, he came up with all kinds of ideas that mixed human-like mobility with mechanical strength. Take the Hardiman I exoskeleton, for example, was designed to provide “super strength for the average man”, with its hydromechanical arms theoretically capable of loading a bomb into the payload of an aircraft. You don’t have to look too closely to see how this design may have inspired the iconic Loader from James Cameron’s Aliens.
At the end of the 1960s, concept artist and futurist Syd Mead created a series of illustrations for a US Steel Corporation brochure. Among the various svelte, futuristic vehicles was a single illustration of a “four-legged, gyro-balanced, walking cargo vehicle.”
Just like the AT-ATs we’d later see in The Empire Strikes Back, Mead’s walking cargo vehicle is shown striding about among ice and. The vehicle, Mead later explained in his art book Sentinel, is capable of tackling all kinds of terrain thanks to its ingenious transforming legs. Those huge feet can also pivot to create wheels – perfect for rolling over smoother ground. Its way of walking, meanwhile, is taken from the elephant: “As he puts his weight on each foot, the metacarpals and tarsals fan out from the ankle and the foot spreads, distributing the pressure. Conversely, as the weight is retracted the foot contracts and never gets stuck in the mud…”
Mead doesn’t say whether he had already seen and General Electric’s Walking Truck when he conceived his walking cargo vehicle, but he does concede that the US Army had already funded research into the project when he was working on his designs. You can read his description from Sentinel at Cybernetic Zoo – an online menagerie of early robots and cyber-animal concepts.
When it came to the AT-ATs in Star Wars, George Lucas was initially inspired by the descriptions of Martian war machines in HG Wells’ classic novel, The War Of The Worlds (the legend that Lucas was inspired by some huge cranes in San Francisco was firmly put to rest in 2008).
Effects artist and art director Joe Johnston, meanwhile, was more immediately inspired by Syd Mead’s illustrations. Johnston even admitted as much in this 2010 interview:
“The snow walkers were from a brochure by Syd Mead for US Steel of these walking trucks going through the snow – we turned them into walking tanks.”
While the walker’s body and head evolved through Johnston’s early sketches, the articulation on the legs and those heavy, elephantine feet remained remarkably close to the ones Mead had come up with. Together with Ralph McQuarrie, who created some dramatic paintings of how the snow walkers would look in battle, the Empire’s deadly war machines gradually took shape.
Early in The Empire Strikes Back‘s production, it was initially suggested that the AT-ATs should be brought to life with robotics – in other words, Industrial Light And Magic would have built five-foot high props capable of walking in front of the camera in real-time. Effects director of photography Dennis Muren, on the other hand, pushed to have the AT-AT sequences hand-animated, and the team eventually adopted a new technique developed by animator Phil Tippett; called Go-Motion, it added a subtle yet realistic hint of blur to a model’s movement.
Taking another cue from Syd Mead, the AT-AT’s distinctive, heavy-footed walk was inspired by the gait of an elephant. Phil Tippett recalls heading to a local zoo, drawing lines on the flanks and legs of an elephant, and filming it as it lumbered from right to left. Those movements were then transferred onto paper and turned into a simplified, hand-drawn animation – or animatic – for the stop-motion effects team to follow. (Fragments of this animatic also shows some of the AT-ATs jumping – an ability thankfully dropped for the finished film.)
The AT-ATs alone took nine months to build all by themselves; the miniature snowy landscape was, in fact, made from a layer of baking soda and tiny beads of glass – the latter glinting under the studio lights as the camera passed across the scene. Then, day after painstaking day, animators Tippett and Jon Berg would pop up through trap doors hidden in the set, move the walker models a millimetre or two, before ducking back down to get the shot. This process was continued over and over again for every single frame; with each second of footage taking up 24 frames, a single shot would often take a day or more to complete.
The result was a breathtaking action sequence that immediately differentiated Empire from the original Star Wars, and still captures imaginations today. Sure, even Star Wars fans may joke about the practicality of the walkers’ designs, but consider this: one of the very early concepts for the AT-AT was a simple tank on wheels. Had Lucas and his team at ILM felt like saving time and money, they could have stuck with this more prosaic design; instead, they opted for the far more challenging and costly four-legged design – simply because they wanted to.
The image of an army of AT-ATs lumbering across a battlefield is such a powerful one that it was reprised for maximum impact in last year’s Star Wars: Rogue One. Over three decades on from their original appearance, the AT-ATs remain a timeless symbol of the Empire’s military strength. Research into four-legged vehicles, meanwhile, is still going on well into the 21st century. Maybe the notion of a walking war machine isn’t so far-fetched, after all…