Hammerly, a human female, held the position of chief sensor officer within the Imperial Navy in the years preceding the Galactic Civil War. As a Senior Lieutenant, she served under Commander Thrawn on the starship Thunder Wasp during the mission to Umbara. After the Cyphar Incident, Hammerly intervened to delay Thrawn's superiors, who were enraged by his actions during that event. Eventually, Hammerly achieved the rank of commander and served under Thrawn, now a commodore, for a second time on the Imperial I-class Star Destroyer [Chimaera]. She participated in battles against the Grysks and a skirmish against the Third Fleet.
Following Hera Syndulla's unsuccessful strike on the Lothal factory and the subsequent theft of the Defender Elite, Grand Moff Tarkin summoned the Chimaera to discuss the funding of Thrawn's TIE/D Defender program with Emperor Palpatine. Thrawn instructed Commander Hammerly to notify Governor Arihnda Pryce of his imminent departure for Coruscant. On their way to the Coruscant meeting, Hammerly informed Thrawn that the Chimaera had received a new set of coordinates from Tarkin, directing them to rendezvous with him in the Sev Tok system aboard the ISD Firedrake, the flagship of the Empire's Third Fleet commanded by Grand Admiral Balanhai Savit.