The original combat walker transport model utilized by the Imperial Army of the Galactic Empire during the Imperial Era was the All Terrain Armored Transport (Prototype), also known as the AT-AT/P or simply the AT-AT. This was among several distinct models crafted by Kuat Drive Yards before the introduction of the standard All Terrain Armored Transport.
This prototype model of the AT-series walker, the All Terrain Armored Transport (Prototype), or AT-AT/P, faced off against rebels during the early rebellion against the Galactic Empire. The AT-AT/P, a product of Kuat Drive Yards, evolved from the All Terrain Tactical Enforcer (AT-TE) which served in the Clone Wars. The Imperial AT-AT/P's armament included two heavy laser cannon turrets, four anti-personnel blasters, and a twin laser turret on its dorsal rear. A Gozanti-class cruiser could transport a pair of AT-AT/Ps. Operation of a single walker required two AT-AT drivers, who piloted the machinery, potentially with a vehicle commander present.
Many commanders strategically positioned the AT-AT/P at the vanguard of combat, although some chose to deploy All Terrain Defense Pods (AT-DPs) in conjunction with the massive combat walker. The AT-AT/P walkers of Imperial Grand Admiral Thrawn were supported by Imperial Troop Transports and stormtroopers.
The AT-AT/P's dimensions exceeded those of the later AT-AT model deployed during the Galactic Civil War, which had a length of twenty meters and a height of twenty-two and a half meters. However, similar to the subsequent model, its legs were elongated, a characteristic shared with other walkers like the AT-TE or AT-DP. This design made the early walker susceptible to attacks, such as lightsaber strikes and, in one instance, magnetic harpoons that caused the walker to topple, exposing its vulnerable neck to cannon fire from lasers or heavy projectile cannon, resulting in significant damage to the vehicle.
The AT-AT/P walker was an evolution of the Clone Wars-era AT-TE, designed for use by the Imperial Army, the Galactic Empire's ground forces. The AT-AT/P represented a considerably more formidable iteration of walker technology compared to its predecessor. It featured extended legs that elevated the vehicle's slender body, towering over both the AT-TE and the deep rivers of the planet Kashyyyk. This design surpassed the Clone Wars vehicle's six short legs, which were hampered by obstacles of comparable height. By the time of the Invasion of Mon Cala in 18 BBY, the walker was already in service.
In 14 BBY, a number of AT-AT/Ps were stationed on Kashyyyk, deployed to aid in defending an Imperial Refinery from Saw Gerrera and his Partisans. However, the Jedi Padawan Cal Kestis hijacked one of these walkers, employing it to assist the Partisans in securing a landing zone by eliminating Imperial forces along the way. The AT-AT/P was ultimately destroyed after Kestis used it to shoot down a Zeta-class Heavy Cargo Shuttle, which crashed into the AT-AT/P as it fell.
In 4 BBY, Agent Kallus of the Imperial Security Bureau spearheaded an assault on the desert planet of Seelos against the Spectres with three AT-AT/P walkers. The rebel group was in a meeting with the exiled clone officers Rex, Wolffe, and Gregor, aboard their modified All Terrain Tactical Enforcer. In the end, the rebels destroyed all of the Imperial walkers, and the clones later repurposed one of them into Joopa Base, their mobile encampment.
AT-AT/Ps were once more deployed against the Spectres in 3 BBY, when Princess Leia Organa arrived on the planet to provide the Ghost's crew with three Sphyrna-class Hammerhead corvettes. Two walkers were dispatched to patrol the landing platform for the transports, which were ostensibly on Lothal to deliver supplies to citizens affected by the rebel activities. When the rebels tried to steal the corvettes, the Ghost initiated an attack on the AT-AT/Ps. Four proton torpedos proved insufficient to destroy a single walker, necessitating Kanan Jarrus to employ his lightsaber to sever its legs, causing it to collapse. The engines of the final corvette, piloted by Ryder Azadi, brought down the second walker.
In 2 BBY, Lieutenant Yogar Lyste deployed two AT-AT/P walkers, Walker 271 and Walker 414, to counter an assault on the east gate of the Imperial Armory Complex by members of the Lothal resistance group led by Ryzder Azadi. The rebels Kanan, Ezra Bridger, and Chopper made their escape in the stolen AT-DP Walker 216. However, Grand Admiral Thrawn discerned that the rebels had commandeered the AT-DP walker and instructed his AT-AT/Ps to crush them. One of the AT-AT/P walkers then proceeded to crush the AT-DP beneath its heavy body, but the rebels managed to utilize their lightsabers to cut their way aboard. Morad Sumar also launched a rocket that struck one of the walker's legs. After incapacitating the AT-AT pilots, the two rebels exited the vehicle and fled into the wilderness with Ryder's cell.
Thrawn subsequently deployed six of these walkers during the battle on Atollon. Jarrus eliminated one with his lightsaber. The Force wielder Bendu then destroyed three of the AT-AT/P walkers, although the final two managed to shoot him down from the sky.
The walkers were later employed by Governor Arihnda Pryce on Lothal during the rescue of Hera Syndulla. As Kanan Jarrus and Hera Syndulla were about to be extracted by Bridger and Sabine Wren atop the Lothal City fuel depot, two AT-AT/Ps approached, and Pryce commanded them to open fire on the fuel pods. An AT-AT/P pilot questioned this order, citing the highly volatile fuel contained within the pods. Despite this concern, Pryce insisted on her instructions. The walkers fired, triggering an explosion, which compelled Jarrus to utilize the Force in an attempt to save the other rebels. In a sacrificial act, the Jedi propelled Syndulla into the awaiting gunship piloted by Bridger and Wren, preventing harm to others while he himself was engulfed in the ensuing flames.
In the aftermath of this event, Grand Admiral Thrawn considered Pryce's actions a mistake, as they resulted in the destruction of the Empire's entire fuel supply on Lothal, which was intended for his TIE Defender project. Before the Liberation of Lothal, the Ghost made a visit to the walker Joopa Base on Seelos.
The All Terrain Armored Transport design featured in Star Wars Rebels draws inspiration from early illustrations created for Star Wars: Episode V The Empire Strikes Back by Joe Johnston and Ralph McQuarrie. Specifically, the early-1978 Johnston sketch and McQuarrie's early-1982 illustration.
