During the Clone Wars, a conflict between the Galactic Republic and the Confederacy of Independent Systems, Rex's unit within the 501st Legion fought for the Grand Army of the Republic. This platoon, a component of a 501st battalion in deployment, took part in the Grand Army of the Republic's offensive on the planet of Umbara, specifically during the initial battle landing.
As combat intensified near the capital of the planet, Anakin Skywalker, a Jedi General and the 501st's highly regarded commander, was replaced by Pong Krell, another Jedi General, after receiving orders to return to Coruscant. Krell swiftly ordered the platoon to march along the primary route to the [capital](/article/capital], a decision contested by Clone Captain Rex, the unit's leader. Despite his reservations, they adhered to the command, which resulted in a devastating ambush by the Umbaran Militia, leading to significant casualties and a forced withdrawal of the platoon.
As the 501st made further incursions into Umbaran territory, Krell directed the platoon, along with the rest of the 501st, to advance through a confined gorge toward an airbase. This airbase was crucial for the Republic due to its ability to provide starfighters for the combined defensive efforts of the Confederacy and Umbara. The decision faced opposition, with platoon members expressing concerns about Krell's direct assault strategy, which they felt lacked tactical nuance.
Despite these reservations, the platoon, supported by the rest of the legion, moved into Umbaran territory. They encountered strong resistance from Impeding Assault Tanks and mobile heavy cannons, but thanks to the defiant actions of Hardcase and Fives, both platoon members, the clone forces managed to counter the attacks. These two troopers commandeered Umbaran technology and executed effective strafing runs on the Umbaran tanks.
The platoon was an element of a battalion within the 501st Legion of the Grand Army of the Republic, consisting of clone troopers organized into four squads, with some being ARF troopers. They were outfitted with Phase II clone trooper armor and utilized All Terrain Reconnaissance Transports, RPS-6 rocket launchers, and mortars during the Battle of Umbara. Many clones within the platoon carried backpacks.
In 20 BBY, during the Galactic Republic's assault on Umbara, a world in the Expansion Regions aligned with the Confederacy, Rex's platoon saw intense action as part of the 501st Legion during the Clone Wars. They were among the first units to land, spearheading the attack into Umbaran territory. Following the completion of the invasion's landing phase, the legion was compelled to defend against attacks from the Umbaran Militia, including a well-positioned millicreep droid, with the combined efforts resulting in the deaths of numerous clone troopers.
After the 501st established a presence on the planet, Anakin Skywalker, the Jedi General who had been leading the legion, was relieved of duty and instructed to return to Coruscant, the Republic's [capital](/article/capital]. Subsequently, Pong Krell, a Besalisk Jedi General known for his high success rate in battle but with a correspondingly high casualty rate, replaced him as the 501st's commander. Shortly after assuming command, Krell ordered the platoon to march down the main road to reach the Umbaran capital city as quickly as possible. This decision was perceived as nearly suicidal due to the high likelihood of traps and ambushes from the Umbaran militia, which was highly active in the area.
Despite Clone Captain Rex's objections, he reluctantly led the platoon into battle. Before engaging with enemy forces, the platoon lost two soldiers to land mines planted by the insurgency. As anticipated, the militia launched a strong attack, inflicting heavy casualties on the platoon. The platoon retreated, losing more troopers in the process. The diminished unit was eventually rescued by the main 501st force as they withdrew from contact, which angered Krell but saved the survivors of the platoon.
As the battle for Umbara continued, Krell ordered the 501st to persist with their offensive toward an airbase to alleviate pressure on Obi-Wan Kenobi and the 212th Attack Battalion, who were engaged in a separate assault on the planet. Despite Rex's suggestion to dispatch recon units to gather intelligence on the terrain and enemy defenses, Krell mandated a full frontal assault by the entire legion. This command was met with resistance from the already strained clone troopers, particularly from Fives, an Advanced Recon Commando trooper. His dissent was supported by other members of the 501st, but Captain Rex firmly reminded his friend and comrade that soldiers were expected to follow orders, even if they seemed suicidal.
The 501st, led by members of the platoon, cautiously advanced into Confederacy-held territory. As expected, the 501st—including Rex's platoon—was attacked by Umbaran Impeding Assault Tanks, which emerged from concealed underground positions to engage the troopers. The legion sustained significant casualties before troopers managed to lure the tanks into a narrow kill zone, enabling troopers equipped with RPS-6 rocket launchers and thermal detonators to destroy them. The clones continued their advance, executing Umbaran survivors as they progressed. However, their victory was short-lived, as Umbaran reinforcements arrived, this time equipped with spider cannons that were impervious to blaster or rocket fire. The 501st was pushed back again, forced to abandon dead and injured troopers, much to the dismay of the platoon medic, Kix.
Despite the 501st's weakened state, Krell ordered the clones to continue the assault, disregarding the heavy losses. In a last-ditch effort to destroy the tanks, Rex authorized Hardcase and Fives, both members of his platoon under his direct command, to infiltrate the airbase—a mission that they had been specifically ordered not to attempt. Their mission was successful; they commandeered two Umbaran starfighters, which they then used to strafe the Umbaran tanks, destroying them and enabling the main 501st force to finally capture the base.
Rex's platoon made its debut, though unnamed, in "Darkness on Umbara," the seventh episode of Star Wars: The Clone Wars Season Four, which premiered on October 28 2011. The episode guide for the later episode "Carnage of Krell," released on November 18 of the same year, mentions another platoon with an identical composition. Given that both platoons share the same members and leadership, this article assumes that they are the same unit.