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


In 2531, the 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.[2]

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.[3] This isolation meant that the Station Gamma Dockmaster AI Doppler was unable to implement the Cole Protocol on the Circumference.[4]

This oversight was detected by Covenant intrusion software, and the Covenant dispatched three frigates full of Elites, Jackals, and Rangers to recover the Prowlers 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 SPARTAN-IIs 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 John-117 met Staff Sergeant Avery J. Johnson. The success of the mission came at a very high cost: SPARTAN-058 was severely wounded and declared clinically dead and SPARTAN-005 was stranded and most likely died when his T-PACK was ruptured by a Type-33 Guided Munitions Launcher needle.[5]


  • In Halo: The Fall of Reach it is stated that on the UNSC Circumference, there is a simple circle (a circumference), where the name should be.



  1. 1.0 1.1 Halo: Ghosts of Onyx, page 186
  2. Halo: Ghosts of Onyx, page 50
  3. Halo: Fall of Reach, pages 269, 281-282
  4. Halo: Fall of Reach, page 302
  5. Halo: Fall of Reach