Chi Ceti IV (Earth-5875)

Chi Ceti IV is the fourth planet in the Chi Ceti system. The planet is home to the Damascus Testing Facility, a top-secret installation located in Vhalkem, where both the the MJOLNIR Powered Assault Armor/Mark IV and the EOD-class MJOLNIR were developed. While mostly military-based, Chi Ceti IV has home to a population of 10,000 civilians.

Battle of Chi Ceti IV
On November 27th, 2525, Chi Ceti IV was invaded by the Covenant CCS-class battlecruiser Unrelenting, when it breached through the Chi Ceti system. While the Paris-class heavy frigate UNSC Commonwealth attempted to drive it off, both ships suffered heavy damage, and the SPARTAN-IIs on the planet received their MJOLNIR Powered Assault Armor/Mark IV.

Hours later, the SPARTAN-IIs John-117, Kelly-087, and Samuel-034 boarded the Unrelenting from the Commonwealth in an operation to destroy the ship from within. Inside the ship, they battled against multiple sangheili and kig-yar, where Samuel's armor was damaged and therefore stopping him from returning to the Commonwealth. He then chose to stay behind and sacrifice himself by detonating an ANVIL-II missile, destroying the Unrelenting. Ultimately, the planet was still taken by the Covenant and glassed, with most of its military and civilian population being killed.