Raid on Polis Massa The raid on Polis Massa was a large skirmish between the Galactic Empire and the Alliance to Restore the Republic on the mining asteroid colony of Polis Massa . This colony was being used by the Rebels in the early days of the Galactic Civil War in 0 BBY . Prologue . When cleaning up after the seemingly minor Death Star Uprising , the Empire had discovered that a few Rebels were able to transport vital information on Imperial plans away from the Death Star . Imperial Intelligence uncovered an active Rebel base on Polis Massa and Darth Vader decided to send troops from his elite fighting legion , the 501st Legion , to recover the plans there before the Rebels could decode them . The battle . Once the 501st Legion arrived at the asteroid base , they executed their raid , taking control of the Rebel radar facility effortlessly . Next , they attempted to storm an elevated command room where the holodisk , supposedly holding the stolen plans , had been located . However , approaching the stairs to the room , dozens of Rebels , including Wookiee warriors , swarmed the hallway at the base of the stairs , killing nearby stormtroopers . A new Imperial wave cut down the exposed Rebels in short order . The data was then removed from the disk and uplinked to the Imperial systems while the 501st were forced to hold strong the radar - communications facility which was now surrounded on all sides by Rebel soldiers . Meanwhile , Imperial agents analyzing the data on the holodisk were shocked to discover it was a decoy . The 501st were left entirely cornered in the radar area . Rebel charges were held off until the uplink was complete . When the 501st were contacted about the questioned legitimacy of the holodisk — now fighting for a lost cause and without further orders — their leaders commanded the men to fight on nevertheless . The tides turned miraculously and the 501st , in an astounding maneuver , broke free and scattered into the rest of the base . While regrouping in different sections of the base , the 501st Legion was thankful to be at last given further instructions : they had to destroy a databank , in an area called the Cavern , which the Rebels were using to eavesdrop on the Empire ' s transmissions . Determined to stop this , the stormtroopers of the 501st fought their way deep into the base and destroyed the databank . Secretly , exhausting stealth work by Bothan spies on the Rebel side had enabled them to beam the plans out of the Empire ' s grasp once again , substituting them with the copies on the holodisk . However , with no other objectives , the 501st Legion at least wanted to crush the Rebels of this base — the insurgents who had humiliated their legendary reputation in an obvious ambush — and escape from the asteroid with their lives . In the end , both would occur . Rebel and Imperial sides piloted the same AAC - 1 Hovertanks in the outside perimeters of the base until Rebels captured the central hangar . Always prepared , stormtroopers raided the hangar furiously , though , and it was firmly secured . Aftermath . When the fighting died down , 501st officers now realized how much they had really diminished the Rebel defenders . With just a few more firefights , the base had been eradicated of Rebels completely . The conquered stronghold was not occupied for much longer , however , before the 501st shut it down and were shipped off on another mission to the Tatooine system . It was not too long later that a rogue ambassador CR90 corvette , " Tantive IV " of Alderaan , had been traced by the Empire - acquired holodisk and was suspected to be the location of the genuine plans . The Empire was not about to be fooled again . Darth Vader would be leading the next attack personally . Behind the scenes . The raid on Polis Massa first appeared in the Pandemic Studios video game " " , which was released on November 1 , 2005 .