R3-A3 was part of a rebel cell based on Mykapo called the Iron Squadron. He served captain Mart Mattin, Gooti Terez, and Jonner Jin and was responsible for maintaining the Sato's Hammer. Mart's father was the leader of the Iron Squadron and his son succeeded him after he died. The Iron Squadron had no contact with other rebel cells including Mart's uncle Commander Jun Sato's Phoenix Squadron. The Iron Squadron constituted the only rebel group in the Mykapo System.
The Iron Squadron later clashed with an Imperial advance patrol. Despite sustaining damage to their hyperdrive, the Iron Squadron managed to destroy their Imperial opponents with the help of the Ghost Crew and Phoenix Squadron. Sato's Hammer destroyed a Gozanti-class Cruiser by dropping several cargo containers containing explosives. Later, the Ghost Crew docked their ship, the Ghost, with Sato's Hammer. Hera Syndulla attempted to recruit the Iron Squadron. The rebels chanced upon R3-A3 repairing the hyperdrive. R3 entered into a fight with the rebels' astromech droid C1-10P, who wanted to fix the hyperdrive. Only Gooti and Ezra Bridger, one of the crew members, managed to break up the fight. Hera's meeting was unproductive since Mart and his crew refused to leave the Mykapo System.
After Ezra convinced Hera to let him have another go at reasoning with Mart, R3 accepted help from Sabine Wren and Chopper to repair the hyperdrive. Despite repairing the hyperdrive, their efforts came to naught when Mart diverted the power to the ship's laser cannons and deflector shields. After Imperial reinforcements under Admiral Kassius Konstantine entered the system, R3 along with Gooti and Jonner heeded Ezra and Sabine's warnings to leave and evacuated aboard the Phantom II. However, Mart decided to stay behind and disengaged the Phantom II. He attempted to attack Konstantine's Imperial Light Cruiser but the ship's engines were disabled. R3-A3 and the other rebels escaped into hyperspace.
R3 later participated in a joint mission by the Ghost Crew and Iron Squadron to rescue Mart. After the rebels learnt that Konstantine had attached a magno-mine to the hull of Sato's Hammer, Hera dispatched R3 and Chopper to remove the mine. The two droids were deployed via the Ghost's cargo bay. R3 was afraid so Chopper pushed him into space. The two droids then activated their rocket boosters and flew to Sato's Hammer. Working together, they removed the magno-mine with R3 removing the magnetic field. The two droids then reattached the mine to cargo box hanging from Sato's Hammer. Under orders from Hera, they entered the ship's cockpit to await pick-up by the Ghost.
R3 reunited with his captain aboard. Shortly later, rebel forces led by Sato arrived and attacked Konstantine's Imperial forces. After the Ghost picked up Sato's Hammer, they dropped the bomb-laded cargo box onto Konstantine's ship. The resulting explosion badly damaged the cruiser and allowed the rebels to flee just as Grand Admiral Thrawn entered the system in the Chimaera. Later, R3 reunited with the other rebels at Chopper Base on the planet Atollon. He witnessed Mart hugging his uncle Jun, Jonner, and Gooti as Chopper bumped him.
Personality and Traits
R3-A3 was a temperamental and territorial astromech droid who maintained the systems aboard the Sato's Hammer. While he was initially bristling at help from Chopper, the two came to form a strong bond and joined forces to repair the ship's hyperdrive and to remove a magno-mine.