CCS-U321 was a Covenant CCS-class battlecruiser that participated in the First Battle of Arcadia. Known only by its UNSC designation, this vessel, along with another battlecruiser, labelled CCS-U624, exited Slipspace near Arcadia on February 9th, 2531. The two vessels were immediately engaged by four UNSC ships. During the battle U321 was caught with its shields down and was destroyed.