There are a variety of walkers: Star Wars Episode V: The Empire Strikes Back introduces the All Terrain Armored Transport (AT-AT) and All Terrain Scout Transport (AT-ST), while Star Wars Episode II: Attack of the Clones, Star Wars Episode III: Revenge of the Sith, and the Star Wars Expanded Universe feature numerous others. Walker variants have been merchandised and featured in popular culture.
The AT-AT is a large, four-legged walker introduced in The Empire Strikes Back during the Battle of Hoth. An AT-AT also appears in Return of the Jedi.
Joe Johnston's original design for the Empire's war machines was a giant, multi-wheeled vehicle; this design later became the "Juggernaut" in West End Games' roleplaying material, and the design was reworked into the clone turbo tank for Star Wars Episode III: Revenge of the Sith. Industrial Light & Magic (ILM) created models ranging from 6 to 50 centimeters in height. ILM filmed the AT-ATs using stop-motion animation against matte paintings created by Mike Pangrazio because attempts at compositing miniature footage against live-action background footage yielded mediocre results. Additionally, ILM studied elephants to determine the best way to animate the four-legged AT-ATs. Although the stop-motion animation style gave the AT-ATs a jerky, "staccato-like" effect on film, ILM found this movement acceptable because of the AT-ATs' mechanical nature. The sound of the AT-AT walking was created by Sound Designer Ben Burtt, by using the sound of an industrial glass cutter.
Dialog in National Public Radio's adaptation of The Empire Strikes Back states that AT-ATs "look like animals"; the character goes on to describe the vehicles as carrying "extremely heavy armor and armaments". The AT-AT, designed to favor "fear over function", can carry five speeder bikes and 40 Imperial stormtroopers. The walkers themselves carry two blasters and two laser cannons. Manufactured by Kuat Drive Yards, Expanded Universe sources describe the AT-AT as being either 15 or 22.5 meters tall. Their armor is resistant to standard blaster weapons; however, the "neck" column of the walker holds no such invulnerability and, if shot, can cause the entire walker to be destroyed.
The AT-ST model used in The Empire Strikes Back was to have more screen time; however, one scene depicting a snowspeeder shooting at the AT-ST model was ruined when the set's background shifted. For Return of the Jedi, ILM made the AT-ST design more detailed. Numerous models were created, including a full-sized AT-ST for on-location shooting. Director Richard Marquand and producer Robert Watts played the AT-ST operators for the scene in which Chewbacca (Peter Mayhew) and a pair of Ewoks commandeer an AT-ST.
Lee Seiler sued Lucasfilm in the mid-1980s, claiming that the AT-ST infringed on his copyright on what he called a "Garthian Strider", which he said he created in 1976 or 1977. The case was dismissed with the court noting that not only did Seiler not produce the supposed drawings at trial, but that the copyright came one year after The Empire Strikes Back debuted.
Star Wars guidebooks describe the AT-ST as a "reconnaissance or defensive vehicle [that] is lightweight and built for speed". Their agility allows them to defend the slower AT-ATs or support other Imperial ground forces. They are 8.6 metres (28 ft) tall (although some sources describe them at seven meters) and seat a pilot and co-pilot. AT-STs are armed with laser cannons on the "chin" and sides, feet claws for destroying small defenses and side-mounted concussion missile launchers.
During the Battle of Endor in Return of the Jedi, the protagonists and the local Ewok tribes capture or destroy many AT-STs, which due to their precariously balanced design prove highly vulnerable to the Ewoks' primitive booby traps. In the Expanded Universe, AT-STs are often featured in Imperial attack forces. Video games such as Star Wars: Rogue Squadron and Star Wars: Shadows of the Empire include numerous AT-STs, and they are player-controllable units in several real-time strategy games. Several walker designs have been influenced by the AT-ST's design.
The AT-TE is a six-legged walker that appears in Attack of the Clones, Revenge of the Sith, and the The Clone Wars multimedia campaign.
Conceived by Ryan Church as a predecessor to the AT-AT, the AT-TE's animation for Attack of the Clones was supervised by Rob Coleman. Tom St. Amand, who previously worked on the AT-AT scenes in The Empire Strikes Back, provided his experience to create a similar appearance for the AT-TE.
AT-TEs are depicted as assault vehicles that appear at the Battle of Geonosis in Attack of the Clones and in various Clone Wars media. Its six legs and flexibility reduce its speed but increase its mobility and stability, and its low speed allows it to walk through energy shields. The vehicles are armed with laser cannons, a powerful projectile cannon, and heavy electromagnetic armor. AT-TEs are manufactured by Rothana Heavy Engineering, a subdivision of Kuat Drive Yards (who manufacture many of the other walkers).
The All Terrain Personal Transport (AT-PT), introduced in Timothy Zahn's novel Dark Force Rising, is a two-legged, one-person vehicle designed for the Old Republic as a "personal weapons platform for ground soldiers." The AT-PT is equipped with two blaster cannons, a concussion grenade launcher, and hi-tech sensors. In addition to appearing in Dark Force Rising, the AT-PT is featured in a number of video games, including the Star Wars: Rogue Squadron series, Star Wars: Force Commander, and Star Wars: Galactic Battlegrounds.
The All Terrain Anti-Aircraft (AT-AA), featured in various Expanded Universe media, is a four-legged anti-aircraft vehicle used by the Galactic Empire. The All Terrain Advance Raider (AT-AR) appears in Marvel Comics' Star Wars series and an All Terrain Experimental Transport (AT-XT) appears in LucasArts' Star Wars: The Clone Wars game. DK Publishing's Attack of the Clones: Incredible Cross-Sections book mentions an All Terrain Heavy Enforcer.
In addition to the AT-TE, other vehicles were created for Clone Wars media and depicted as predecessors to the walkers featured in the original trilogy. One such walker is the two-legged All Terrain Attack Pod (AT-AP), a variation of the AT-PT, seen in Revenge of the Sith and Clone Wars media. Alex Jaeger designed the AT-AP per Lucas' request to "diversify the Clone armor". The AT-AP features a variety of artillery weapons, a retractable third leg for stability, and other offensive features.
The All Terrain Open Transport (AT-OT), also seen in Revenge of the Sith and other sources, is a heavily armored transport whose open design makes it vulnerable from above. The AT-OT can transport 34 clone troopers. During the late stages of Revenge of the Sith's development, it was called the "Clone CAT walker".
Clone troopers mounted on All Terrain Recon Transports (AT-RT) search for Yoda (Frank Oz) on Kashyyyk in Revenge of the Sith. The AT-RT is described as a precursor to the AT-ST. A scene cut from Revenge of the Sith would have shown Yoda distracting clone troopers while Chewbacca removes them from their AT-RT in a manner similar to how he wrests control of an AT-ST in Return of the Jedi. AT-RT animators studied AT-STs' movements to recreate "some of the original funkiness of movement" that came from the stop-animation style used in the original trilogy.
Kenner released AT-AT and AT-ST toys as part of their Empire Strikes Back line, and Hasbro released toys based on those molds when the Special Edition trilogy was distributed. Micro Machines also released AT-AT, AT-ST, and AT-TE toys. Both Decipher Inc. and Wizards of the Coast published AT-AT and AT-ST cards for their Star Wars Customizable Card Game and Star Wars Trading Card Game, respectively. Lego has released AT-AT, AT-ST, AT-AP and AT-TE models.