UNSC Circumference

The UNSC Circumference was a UNSC Office of Naval Intelligence Prowler.

Background
In 2531, Circumference transported SPARTAN-IIs 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 Battle of Reach, Circumference was docked at Reach Station Gamma, Bay 9. 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 Elite Rangers to recover the Prowlers NAV database. Three SPARTAN-IIs (John-117, Linda-058, and James) 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. It was during the mission to destroy the NAV database that SPARTAN-117 met Staff Sergeant Avery J. Johnson. The mission also cost severe injuries to SPARTAN-058, and possibly killing James.