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Previously an Imperial Hive World known as Agrellan, the planet was captured by Commander Shadowsun and Ethereal Supreme Aun'va during the Third Sphere of Expansion. During the ensuing Battle of Mu'gulath Bay, Tau XV104 Battlesuits proved decisive in defeating the Imperial Guard heavy tanks which guarded the world's capital Hive.[1a] The battle to capture the planet has been the largest of the Third Sphere of Expansion, and no less than twelve advanced weapons prototypes were used by the Tau. Only the fusion reactor meltdown that destroyed Mu'gulath Bay's moon proved a failure.[1b]
Shortly after the Prefectia Campaign the Imperium launched a major counterattack against Mu'gulath Bay, determined to reclaim it. In the end the Tau managed to resist, but the Imperium subjected the planet to Exterminatus and destroyed it. Elements of Mu'gulath Bay's Tau population managed to survive thanks to a shield erected by the Earth Caste.
The esoteric weapons of the Mechanicus proved far more formidable than originally though however. Mu'gulath Bay had to be abandoned as the entire Damocles Gulf was set ablaze, separating the Imperium from Tau Empire. Surviving elements from Mu'gulath Bay attempted to flee to the Farsight Enclaves, but were set upon by Commander Surestrike at the order of the Ethereals. Surestrike managed to destroy most of the rebel Tau, but some managed to escape.
- 1: Codex: Tau Empire (6th Edition)
- 2: War Zone Damocles: Kauyon, pg. 119
- 3: War Zone Damocles: Mont'ka — Imperial Withdrawal
- 4: Codex: Tau Empire (8th Edition) pgs. 37–38