From Halopedia, the Halo wiki
In 2531, the Circumference transported SPARTAN-II Blue Team to investigate Station Delphi in the Groombridge 34 System. During the mission, SPARTAN-051 was abducted to train the SPARTAN-IIIs. By 2552, the prowler was part of Operation: HYPODERMIC.
Prior to, and during, the Fall of Reach, Circumference was docked at Reach Station Gamma, Bay 9, undergoing final stealth upgrades. In an effort to maintain the secrecy of HYPODERMIC, the prowler was removed from Reach's database after an intrusion into the ONI database by the AI Cortana. This isolation meant that the Station Gamma Dockmaster AI Doppler was unable to implement the Cole Protocol on the Circumference.
This oversight was detected by Covenant intrusion software, and the Covenant dispatched three frigates full of Sangheili and Kig-yar rangers to recover the Prowler's NAV database. Three SPARTAN-IIs (John-117, Linda-058, and James-005) were diverted from defending Reach's Orbital Defense Generators to prevent this. The SPARTANs were successful, using the weapons of a commandeered Pelican to destroy the Circumference and the NAV database contained within. The mission also led to very severe injuries to SPARTAN-058 and the probable death of SPARTAN-005 when his T-PACK was ruptured by a needler shard.
List of appearances