War over Hylas

Neither the Imperium nor the Tau were slow to react to the unexpected invasion of Hylas by the Space wolves at the end of 01.012M42. The Imperium, led by Inquisitor Xanthus, were keen to keep the pressure on the Tau and conquer Hylas quickly, while Shadowstrike, now in charge of all sector Tau forces, was desparate to counter attack as soon as possible. Meanwhile Inquisitor hathek, bitterly disappointed at events in the Mabb nebula, abandonned the Tau treaty, at least for the time being. In the Perseus Deeps, where Hathek held overall influence over events, he could ensure that Tau worlds were not targets of Veers' Crusade. However in the Mabb Nebula, he had no way of stopping Xanthus and his allies.

As it happened, the Tau already had one fleet in place to defend Hylas, commanded by Admiral Shinobi. However Xanthus was able to augment his forces by leveraging his contacts in the Adeptus Mechanicus. By 0302.012M42 he was able to assemble a force of three Imperial Guard regiments, escorted by a powerful Adeptus Mechanicus battlegroup, which arrived at Hylas only two days later.

Shinobi handled his fleet with more experience, using a nearby asteroid field as cover from the Imperial nova cannons. Unfortunately his fleet captains were inexperienced, and when they attempted to navigate the belt, several vessels were badly damaged. Rather than risk total annihilation, Shinobi withdrew, and the Imperial guard regiments were landed on Hylas, eliminating the remaining Tau defenders.

The Adeptus Mechanicus fleet then withdrew, their mission complete, while the Space Wolves awaited pick up by their fleet. The intention was to leave the 3 guard regiments behind to mop up any disorder and generally restore Imperial rule. Two days later however, Shadowstrike's fleet arrived.

Shadowstrike's modern Tau vessels quickly took up station above the world of Hylas before the Space Wolves arrived to pick up their ground troops. They were able to take the Imperial fleet by surprise, and the Astartes vessels found out to their horror that the new Tau vessels were much more effective than the older ships they had been used to fighting. Approaching each other head on the superior firepower of the Tau soon told, and the Space Wolves were sent packing without causing much damage to the Tau. Now the ground war began again, as Shadowstrike took back key installations from the Imperium before they had a chance to properly dig in. The war on Hylas went on and the Tau shelved the idea of a peace with the Imperium, who they had mistakenly believed spoke with one voice.