The Battle of Somnus IX was a major battle in the Great War. The UNSC listening outpost on Somnus IX had been able to learn of the incoming Covenant Battlegroup and re-purposed all available ships in the area to it's defence. After a brief naval battle on November the 22nd 2531 the UNSC set up Mass Accelerator Cannons on the planet. Covenant ground forces landed and fought the UNSC on the ground. They were able to destroy the MACs, although they lost a large amount of forces doing so. The UNSC retreated from the system on March the 8th 2532, and Somnus IX was glassed.