During the era of the Galactic Civil War, D-127X served as a probe droid for the Alliance to Restore the Republic. Its clandestine mission involved observing communications and data within the Imperial networks of the Oplovis sector, with a particular focus on collecting information about the Oplovis Sector Fleet. D-127X's mission came to an abrupt end when an Imperial picket ship detected it during a patrol. In response, it launched its messenger droids to relay information back to the Atrivis Sector Force before erasing its memory and initiating self-destruction.
Mon Mothma acknowledged the droid's act of self-sacrifice in her written work A Call to Reason. She attributed the safeguarding of Mantooine from a possible Imperial assault to D-127X's actions. Furthermore, she cited it as proof that even probe droids, often thought to be less advanced, possess a degree of autonomy.