UNSC Circumference

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Ship history
The Unified Earth Government logo Unified Earth Government


Office of Naval Intelligence


Destroyed by enacting the Cole Protocol on August 30, 2552.[1]

General characteristics



Electronic warfare:

Jamming capabilities[2]


Pulse cannon[2]


UNSC Circumference was a prowler operated by the United Nations Space Command during the Human-Covenant War.[3] It was ultimately destroyed during the space conflict during the Fall of Reach, as the victim of the Cole Protocol's enactment by SPARTAN-II Blue Team.

Unlike the UNSC Prowler Corps' mainline prowler classifications, Circumference served in its stealth role as part of a unique type of vessel - taking the form of a stealth ship disguised to resemble a sleek private civilian yacht.[3][1] These characteristics were reflected in the ship's exterior appearance, alongside its innocuous name - similar to other vessels such as UNSC Lark and UNSC Applebee.[3] Accordingly, the ship did not have its name painted on its exterior hull, instead simply displaying a circle (or circumference).[1]

Service history[edit]

Mission to Station Delphi[edit]

Circumference was active in UNSC service by 2531. On November 7 of that year the ship was involved in an operation set up by the Office of Naval Intelligence to deploy Blue Team to investigate the decommissioned shipard for potential suspicious activity. Among emerging from slipstream space, Circumference's sensors had detected a remote ping of another prowler - though this was dismissed by the ship's navigation officer as an echo from the slipspace jump that had bounced off the moon. Following this, Circumference detected an inert communications satellite on the dark side of the moon Station Delphi was orbiting, causing the vessel to target the satellite with a jamming attack and a burst from a pulse cannon. As the Spartan team's mission progressed, they sent numerous status reports back to Circumference though the mission ultimately ended in disruption due to the accidental activation of Kurt-051's T-PACK module at 1000 hours - causing him to be sent flying off into deep space and declared missing in action.[2]

Circumference spent the next 322 minutes (roughly 5.3 hours) searching for Kurt following the estimated time his MJOLNIR Powered Assault Armor would have run out of oxygen, joined by the frigate UNSC Tannenberg at 1105 hours. Once this time was up, the search was called off due to Covenant activity in the region. Ultimately, the entire operation had been devised by ONI Section Three as a ruse to discretely remove Kurt from service to begin the SPARTAN-III program, with Circumference's crew seemingly unaware of the plan.[4][5]

Fall of Reach[edit]

Circumference was still in naval service as of August 30, 2552. At 0400 Military Standard Time on this day, Circumference (alongside other similar prowlers UNSC Applebee and UNSC Lark) were present within the Gamma Station space docks orbiting Reach, and were noticed as part of counterespionage operations conducted by Cortana against James Ackerson.[3] In reality, these vessels were assigned as part of Operation: HYPODERMIC - a top-secret operation being conducted by the UNSC and monitored by Codename: COALMINER and Codename: SURGEON to scout out potential operating bases for the Covenant invasion forces. Circumference and its comrades were docked at Gamma Station to undergo upgrades to their stealth systems, though queries from Cortana's probing were determined by COALMINER to be a risk to the discovery of the ships. Consequently, Circumference's ship registry number was scrambled and the ship was completely disconnected from the dock's computer network - resulting in Gamma Station being totally unaware that Circumference was docked inside it.[6]

Consequently, when the Covenant invasion arrived at Reach to begin the fall of the planet, Gamma Station's AI Doppler was completely unable to access Circumference's systems and enact the Cole Protocol - leaving the ship's navigation database unsecured and vulnerable to capture by Covenant forces. Consequently, John-117, Linda-058 and James-005 were dispatched to Gamma Station to deal with the threat and manually destroy Circumference.[7] Aboard Gamma Station, Blue Team were able to successfully reach Circumference, using the M370 autocannon and Anvil-II missiles aboard a commandeered D77-TC Pelican to destroy Circumference. This was followed-up by John-117 manually entering the ship's remains to destroy the navigation database by shooting it with his MA5B assault rifle. The Spartans then departed Gamma Station, to return to UNSC Pillar of Autumn - the mission having caused the death of James-005 and the near-fatality of Linda-058.[1]

Production notes[edit]

Visual appearance[edit]

In the comic Halo: Fall of Reach, Circumference is erroneously-depicted as an unidentified prowler classification, using artwork of UNSC Red Horse traced from the motion comic of The Mona Lisa. At the time, Red Horse was the only prowler clearly depicted on screen in visual media, and thus used by the artists on the comic as reference. In the original Halo: The Fall of Reach novel, Circumference is described as having been disguised as a private civilian yacht, hence its fairly innocuous name.[3] Due to this, this article treats the ship as described in the original Fall of Reach novel, with the visual appearance in the comic adaptation one of several inconsistencies present in the comic adaptation.


The original Halo Encyclopedia and its 2011 reprint provide a length statistic for Circumference of 162 meters (532 ft). This figure is intentionally ignored by this page, due to the stat being universally applied to all prowlers irrespective of class - including other vessels such as the Sahara-class UNSC Dusk.[8] This figure comes from a series of assumptions made by fans on Halopedia during the mid-2000s, which were copied into the Encyclopedia book wholesale. A statement provided in Halo: Ghosts of Onyx states that the construction cradle for a Point Blank-class stealth cruiser is the same size as a UNSC destroyer. At the time of Ghosts of Onyx's publication, the class of the destroyers was said to be seven metres longer than a UNSC frigate - with the only frigate in existence at that time being the Stalwart-class light frigate featured in Halo 2, which was 478 meters (1,570 ft) long based on extracted files.

As such, fans placed the destroyer and stealth cruiser at 485 meters (1,590 ft) long. In the same chapter of Ghosts of Onyx which mentions the destroyer size, it also specifies the construction framework as three times the size of Circumference - taking this extremely literally gives an equation of 485/3 and a result of 161.66. As such, the length of Circumference provided in the Halo Encyclopedia was originally taken from some dubiously-reliable statements originally published on this page, and are now not considered reliable as a source.


List of appearances[edit]


  1. ^ a b c d Halo: The Fall of Reach, chapter 35
  2. ^ a b c Halo: Ghosts of Onyx, chapter 3
  3. ^ a b c d e Halo: The Fall of Reach, chapter 28
  4. ^ Halo: Ghosts of Onyx, chapter 4
  5. ^ Halo: Ghosts of Onyx, chapter 5
  6. ^ Halo: The Fall of Reach, chapter 30
  7. ^ Halo: The Fall of Reach, chapter 34
  8. ^ Halo Encyclopedia (2011 edition), page 259