A squadron of B1-series battle droids was used by the Galactic Republic during the Clone Wars. The unit had been captured by the Republic and reprogrammed to serve it, participating in a mission to free Jedi Master Even Piell from the Confederate prison known as the Citadel. The battle droids served under R2-D2 and brought the Republic strike team into the Citadel in shuttle 81572. During the ensuing battle, all units were destroyed when they were ordered to cover the retreat of the rest of the team.
By 20 BBY, the Galactic Republic came into possession of three B1-series battle droids which were reprogrammed to follow orders from the R2-series astromech droid R2-D2.
After a fleet of warships from the Confederacy of Independent Systems managed to capture Jedi Master Even Piell while in possession of secret hyperspace coordinates known as the Nexus Route, these droids were assigned to participate in a Jedi-led effort to rescue Master Piell from a Separatist prison located on Lola Sayu called the Citadel. Being led by R2-D2 into one of the Jedi Temple's hanger bays to prepare a captured Separatist Sheathipede-class transport shuttle designated Shuttle 81572, the droids began to load the shuttle with cargo before loading the carbon frozen members of the Citadel strike team into the shuttle. One of the strike team's leaders, Jedi Knight Anakin Skywalker hoped that carbon freezing each of the members of the strike team and loading them into a shuttle piloted by reprogrammed battle droids would fool the Separatists' life-form scanners protecting the Citadel from enemy infiltration.
After departing from the Jedi Temple and exiting hyperspace over Lola Sayu one of the droids, designated OOM-10, would contact Citadel command requesting access to the Citadel, claiming that their shuttle was carrying supplies and frozen rations. As Skywalker had planned, the Separatists' life-form scanners were unable to detect any life forms aboard the shuttle allowing the battle droids to safely land on Lola Sayu's surface near the Citadel. Upon landing, the droids began offloading each member of the Citadel strike team off the shuttle allowing R2-D2 to free the mix of Jedi and clone troopers from carbonite.
After freeing each member of the strike team from carbonite, R2 and his battle droids were ordered to remain with the shuttle until they were summoned for extraction once Master Piell had been rescued. However, Master Piell did not hold the entire coordinates for the Nexus Route himself, with his captain possessing the other half which forced the strike team to also rescue Piell's surviving Republic officers to escape with the full codes. In doing so, the strike team was forced to split up and delayed the droid squadron's arrival at the Citdel, a detail which became quickly noticed by the Citadel's warden, Osi Sobeck. Later, after managing to evade Separatist forces and rally to a potential rendezvous point, Skywalker ordered R2 and his droids to pick up Obi-Wan's half of the strike team, assuming they were still on schedule.
However, upon touching down at one of the Citadel's landing pads, R2 and his battle droids were confronted for their shuttle's late arrival by the Citadel's T-series tactical droid, K2-B4. Following another reprogrammed droid's suggestion to improvise, OOM-10 and the other two battle droids pointed their E-5 blaster rifles at R2 to make it appear that R2-D2 was a traitor and had been apprehended by the battle droids. Managing to fool the tactical droid, K2-B4 ordered R2-D2 to be taken to the interrogation level, with OOM-10 escorting R2 into the Citadel with the other droids. Once alone within one of the Citadel's elevators, OOM-10 apologized to R2 for the deception before requesting orders. R2 expressed his concern that if they were no longer present at the shuttle to extract Obi-Wan's half of the strike team, then they would most likely be walking into a Separatist trap. Understanding the severity of this, OOM-10 stated that will try to locate them if they get captured. R2 and his battle droids then moved to discover Obi-Wan's position, plugging into one of the Citadel's access ports, R2 learned of Obi-Wan's capture and that Sobeck was having his half of the strike team moved to the interrogation level. Intercepting a pair of security battle droids escorting Kenobi's team, OOM-10 pressured the security droids into handing over the prisoners to their droid squadron. Unaware of the droid's reprogramming, the security droids relinquished their prisoners to OOM-10, who promptly led them to R2-D2, freeing the prisoners before retreating towards the now captive shuttle, still being escorted by the reprogrammed battle droids as prisoners to avoid suspicion.
Arriving at their shuttle, which was now under heavy guard by the Citadel's defense forces, including a series of four massive turbolasers positioned just above the landing pad, the reprogrammed droids attempted to gain access to the shuttle, informing the pair of B1 battle droids guarding it that they had orders to transfer the prisoners from Citadel to Point Tarron. Despite confusion from one of the B1s regarding the absence of any outpost at Point Tarron, OOM-10 pressured the droids to let them aboard. However, just as the strike team prepared to board the shuttle, K2-B4 contacted the droid security altering them that the Republic was attempting to escape using reprogrammed battle droids, ordering them to let no one aboard the shuttle. Realizing their cover was blown, the strike team quickly moved into action, eliminating the droids guarding the shuttle before being forced to take cover when the turbolasers began to open fire. R2's battle droids moved quickly to rearm each of the Republic prisoners with their weapons before receiving extra support from Skywalker's half of the strike team, just as a wave of Separatist reinforcements arrived in on the landing pad. Attempting to push back against the Separatists, R2's battle droids joined with the rest of the strike team in assaulting the Citadel's reinforcements from the rear end of the landing pad, only to be forced to retreat when one of the ARC Troopers assigned to the strike team attempted to forcefully retake the shuttle, resulting in it being destroyed by one of the still active turbolasers.
Contacting Jedi Master Plo Koon at the Jedi Temple for reinforcements, the survivors of the strike team began to wander through Lola Sayu's rocky terrain, accompanied by R2's battle droids, fending off small attacks from an army of pursuing BX-series droid commandos and crab droids. When the strike team was cornered by the Separatists at the edge of a massive cliff, Skywalker ordered R2's battle droids to hold off the enemy's advance for as long as possible, hoping to cause enough of a diversion so that the rest of the strike team could escape. Accepting their final orders, all three battle droids marched against the advancing Separatist forces, being quickly destroyed as the Separatists moved to continue their pursuit of the strike team.
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- Star Wars Encyclopedia of Starfighters and Other Vehicles