EXD - 9 ' s infiltration of Chopper Base In 2 BBY , the Imperial Grand Admiral Thrawn began deploying E - XD infiltrator droid s to several Outer Rim planet s . One of them , EXD - 9 , landed on Atollon , home of Phoenix Cell ' s Chopper Base . EXD - 9 was soon ambushed by several krykna spiders and knocked out . The damaged Infiltrator droid was later found by Captain Garazeb Orrelios and Chopper , who brought the droid back to their base . Mistaking EXD - 9 for a protocol droid , they assigned it to help AP - 5 manage the base depot ' s inventory . After learning that EXD - 9 was an Imperial Infiltrator droid , Zeb , Chopper and AP - 5 joined forces to overpower and deactivate the droid . To prevent the Empire from discovering the location of Chopper Base , the rebels sent it back to its Star Destroyer with its proton warhead set to detonate when the droid reconnected to the Imperial network . EXD - 9 subsequently managed to destroy the Star Destroyer , but the incident Thrawn helped narrow down his search for the rebel base to the 94 systems where the droids had been sent . Prelude . In 2 BBY , Grand Admiral Thrawn began deploying E - XD infiltrator droid s to sweep the Outer Rim Territories for rebel bases . Against Imperial mandate , these droids were fitted with a proton warhead that would self - destruct in the event that they were captured . The droids had two forms : combat mode , in which they were extremely fast and agile ; and protocol mode , in which they appeared to be harmless protocol droid s . One of these droids , EXD - 9 , landed on the planet Atollon , which was the location of Phoenix Cell ' s Chopper Base . After landing , EXD - 9 was attacked by two krykna , tough spider - like creatures native to the planet , and temporarily disabled . EXD - 9 ' s arrival coincided with most of the Phoenix rebels , including most of the Spectres , departing on a training exercise . The Lasat warrior Garazeb Orrelios was tasked with overseeing the base ' s security . The rest of the stay - behind party included the C1 - series astromech droid Chopper , the RA - 7 protocol droid AP - 5 , and a communications officer stationed at the command center . After the comms officer reported that a sensor beacon in Sector 6 had apparently been knocked out by meteors , Zeb and Chopper went to investigate . The mission . Intruder alert . Upon arriving , Zeb and Chopper , after replacing the sensor beacon , found EXD - 9 amidst a pile of dead krykna . They mistook it for an old protocol droid . Taking pity on the stray , damaged droid , Zeb brought EXD - 9 back to Chopper Base . Chopper suggested destroying the droid right then and there , but Zeb overruled him . At the base , AP - 5 recharged the droid , who began scanning the depot . Due to damage sustained from the krykna attack , EXD - 9 did not initially remember its mission . Believing that EXD - 9 would make a good inventory droid , AP - 5 hired the " protocol droid " as his assistant . Later , Zeb received a transmission from Fulcrum warning that the Empire had deployed Infiltrator droids and that they had lost contact with one of them . After viewing the schematics , Zeb realized that EXD - 9 was an Infiltrator droid . Fulcrum was actually the disillusioned Imperial Security Bureau Agent Kallus , who had been aiding the rebellion by providing them with intelligence on Imperial activity since his encounter with Zeb on Bahryn . Kallus had recently been alerted that one of the Infiltrator droids had failed to report back and , suspecting that the rebels had it , had stalled for time by claiming that the Empire did not have time to chase down every instance of temporary comm failure , and that they would only investigate if the droid failed to report back in one cycle . In his transmission , he also warned that if the droid did not report back , the Empire " would " come looking for it . Zeb returned to the depot just in time to warn AP - 5 and Chopper before EXD - 9 transformed into its attack mode . The droid had remembered its true identity and mission after AP - 5 used the term " rebel base " . The Infiltrator droid attacked the rebels and fought with Zeb . During the struggle , Zeb managed to sever part of the droid ' s left hand . Damaged , EXD - 9 retreated to recharge and repair itself . It attacked another astromech droid and a GNK - series power droid , draining their power and cannibalizing their parts to recharge and repair itself . Due to the damage sustained earlier , EXD - 9 ' s power readings were so low that Chopper could not detect the infiltrator on his scanners . In response , Zeb and the droids devised a plan to lure EXD - 9 out of hiding so that they could disable it . Return to sender . Chopper managed to lure EXD - 9 out of hiding , and Zeb attacked the droid with the electrostaff mode of his bo - rifle . It was too dangerous to shoot at the droid because they were in the weapons depot , surrounded by high explosives . Following a fierce struggle , Zeb managed to pin down the Infiltrator droid long enough for AP - 5 to disable it . When the droid began activating its proton warhead , Chopper managed to freeze the timer before it could initiate detonation . The rebels then faced a dilemma . Knowing that the Empire would search for the droid , they also had to protect the secrecy of Chopper Base . AP - 5 also pointed out that , since the countdown had already begun , the warhead ' s detonation was inevitable . After some discussion , Zeb and the droids decided to reactivate EXD - 9 to its disarmed mode and return the droid to its base with the proton warhead . AP - 5 also set EXD - 9 to explode once he had reconnected with the Imperial network . After reactivating EXD - 9 , Zeb , AP - 5 , and Chopper allowed the Infiltrator droid to walk back to its pod . Tailing EXD - 9 , Zeb shot out the pod ' s long - range transmitter . This forced EXD - 9 to take its pod back to the Imperial Star Destroyer it had launched from . Upon arriving , two Imperial Navy technicians connected EXD - 9 back to the Imperial network . This caused the Infiltrator droid to initiate its proton warhead countdown and detonate , which also destroyed the other Infiltrator droids . The subsequent chain reaction of powerful explosives tore the Star Destroyer apart . The explosion was watched by Agent Kallus and several Imperial officers aboard a nearby Star Destroyer . While expressing shock and anger publicly , Kallus privately smiled . Aftermath . The following day , Zeb contacted Hera Syndulla and the other Spectres to inform her about the incident , but that they had things under control . The Spectres later attended a briefing at Chopper Base ' s command center , where they received a message from Fulcrum congratulating them for reprogramming the Infiltrator droid that he had warned them about and setting it to self - destruct . AP - 5 tried to tell the other Spectres the whole story , but an embarrassed Zeb shut him up . Grand Admiral Thrawn learned about EXD - 9 ' s role in the destruction of the Star Destroyer from Kallus , and complimented the ingenuity of the rebel plan . Despite the setback , Thrawn was in good spirits because he had narrowed his search for the Phoenix rebel base down to the 94 systems the droids had been sent to . He vowed to crush the rebellion once and for all . Behind the scenes . EXD - 9 ' s infiltration of Chopper Base served as the main plot of the " Star Wars Rebels " episode " Warhead " , which first premiered on January 14 , 2017 . The plot background and details were further expanded in a " Rebels Recon " video hosted by Andi Gutierrez and Pablo Hidalgo .