AX-235 was a Rebel outpost hidden in the asteroids of Cron Drift to monitor Imperial transmissions detected by some communications satellites, stolen from Orron III. It was the very outpost that intercepted an Imperial transmission with the schematics of the Death Star.
Due to the importance of the information, the Alliance dispatched Biggs Darklighter in an T-65 X-wing starfighter to retrieve it. However, after leaving AX-235, Darklighter's X-wing broke down and he came under attack by Imperial forces. The Independence sent three R-22 Spearheads to protect him until a rescue team could arrive and repair his ship. After escaping the attack he delivered the plans to the Independence.