Circinius IV

Circinius IV was a Unified Earth Government colony world in the Circinius system. The planet was orbited by at least three natural satellites. It was the location of the Corbulo Academy of Military Science, an officer training school for the offspring of high-ranking UNSC officials. The space elevator located at Corbulo Academy was considered one of the planet's most spectacular sites.

Covenant attack
After the first engagements on Harvest, ONI Section II kept the Covenant invasion secret from the general population. However, Corbulo Academy's superintendent, General Black, was informed. As preparation for a possible attack, Black discreetly increased the readiness of the UNSC Marine garrison posted in the academy and authorized limited communications blackouts under the guise of routine maintenance procedures.

The colony and the academy were attacked by the Covenant during the earliest days of the Human-Covenant War on April 26, 2526. Orbiting UNSC vessels soon deployed Orbital Drop Shock Troopers directly onto Corbulo Academy's campus. The planet's space elevator was also destroyed, killing many of the escaping cadets as it fell. During the battle, the Covenant killed almost the entire population of the planet. Only four cadets from Corbulo Academy survived the initial assault, although one of them, Chyler Silva, died during the battle. Later, the planet was glassed by the Covenant.

Trivia
Along with Hat Yai, Circinius IV is not mentioned in the Assembly's report on glassed worlds (dated January 1, 2530) in data pad 14 from Halo: Reach. From a real-world perspective, the obvious Doylist explanation is that the planet was created after the game's release, there is no clear in-universe reason for this omission.

List of appearances

 * Halo 4: Forward Unto Dawn
 * Halo 4
 * Halo 2: Anniversary
 * Halo 5: Guardians