R3-A3 was an R3-series astromech droid and member of a local rebel cell on Mykapo called the Iron Squadron. He was responsible for maintaining the Sato's Hammer's systems and customized it to his own specifications. Following a skirmish with an Imperial patrol, R3-A3 and his fellow rebels came into contact with the Spectres and Phoenix Squadron. While initially reluctant to leave, R3 and his comrades Gooti Terez and Jonner Jin heeded the warnings of Ezra Bridger and Sabine Wren and managed to escape the system. However, their leader Mart Mattin was left behind. R3 took part in a combined rescue effort to save Mart. He joined forces with the astromech droid Chopper to remove a magno-mine attached to Sato's Hammer.