New Cerberex: Rideau and Vincennes fall to Tau

On New Cerberex the presence of the Dark Angels had paused the Tau offensive, which had been based around a lighting attack to catch the Imperium off balance before they could create a stable defensive line. As that hadn't happened, the Librian Guard had been able to erect defences, particularly around the capital of New Feducia.

The tau based their next offensive to take advantage of the relative weakness of the Librian left flank, and in 10.023M42 drove an entire hunter cadre into the Vincennes valley, quickly pushing the Librian front line back and threatening to encircle the capital. The imperial force responded with a highly mobile armoured and mechanised force, but found the tau vehicles in particular difficult to take out. The tau used the terrain well, keeping their hammerheads well concealed, and the overall tau force had been created with the possibility of facing either mechanised or astartes forces.

The battle developed favourably for the tau who were able to destroy many of the Librian vehicles, establishing a commanding position over the Vincennes valley. The remnants of the Librian force withdrew, ceding the town of Vincennes to the Imperium and resulting in the encirclement of the capital, for only moderate or "acceptable" casualties.