Battle of Voltoris
Following the disastrous Imperial defeat in the Battle of Mu'gulath Bay, Imperial commanders held a council of war and agreed to stage a deliberately slow retreat towards the Feudal World of Voltoris. This they hoped would draw in the pursuing fleet of T'au Commander Shadowsun and allow for an ambush that would annihilate the Xenos.
The Imperials prepared most of their ambush in Voltoris' most defensible area, the fortress of Furion Peak. The T'au, overconfident in their orbital scans, vastly underestimated their defeated enemy and did not realize that forces including Colonel Straken's Catachan Jungle Fighters, Kor'sarro Khan's White Scars, and Shadow Captain Shrike's Raven Guard had all taken up positions on the planet. The T'au were fooled by the efforts of the White Scars Stormseer Sudabeh, who cast a psychic mist over their positions.
Thus when Shadowsun's army made planetfall at the foot of Furion Peak, the Imperial trap closed. The T'au were baffled by the psychic abilities of the White Scars' Stormseers, who then led a charge to engage their foes at close range. Shadowsun managed to hunt down and kill Sudabeh, but the Imperials were closing their trap and scores of Imperial Knights soon appeared, blasting the T'au army until the forest road had been destroyed. Many of Shadowsun's most trusted teams had to give their lives to secure her escape. She swore after the battle that their sacrifice would not be futile, and that she would redouble her efforts in the Third Sphere of Expansion. This led to Shadowsun executing the Prefectia Campaign shortly after.