The Battle of Chi Ceti was a battle between the UNSC Commonwealth and the Covenant vessel Unrelenting in the Chi Ceti system on November 27th, 2525. While transporting the Spartan-IIs to the Damascus Testing Facility on Chi Ceti IV to receive their MJOLNIR Mk. IV Powered Assault Armor, the Commonwealth is intercepted by the Unrelenting. After a brief encounter, the Commonwealth was able to temporarily disable the Unrelenting and transport the Spartan-IIs planet-side to retrieve their armor.
During armor testing, the Commonwealth was reengaged by the Unrelenting and the Spartan-IIs were forced to transit back to the frigate to assist in the battle. En-route, John-117, Kelly-087, and Samuel-034 went EVA along with three nuclear warheads and infiltrated the Unrelenting, placing the warheads inside the Covenant vessel. During the ensuing firefight, Samuel-034's MJOLNIR armor was breached, leaving him incapable of returning to the Commonwealth. Samuel-034 remained behind to ensure the warheads detonated successfully.