The Zeist Campaign was a military conflict fought between the Imperium of Man and the T'au Empire in the Zeist Sector of the Ultima Segmentum. Taking place in 303.999.M41, during the T'au Empire's Third Sphere Expansion, it ran concurrently with Abaddon the Despoiler's 13th Black Crusade and the assault on Imperial space by the Tyranid Hive Fleet Leviathan during the Third Tyrannic War.
As the Imperium's military was heavily involved with preventing the breakout of the forces of Chaos from the Cadian Gate on the other side of Imperial space, the T'au took advantage of this distraction to rapidly expand their territory. Despite victory belonging to the Imperium, the Zeist Campaign merely allowed the shrewd T'au Commander Shadowsun to rapidly strike deeply into more valuable Imperial space elsewhere.
By the time the Zeist Campaign ended, the T'au's Third Sphere Expansion had already enlarged the T'au Empire by 133% of its prior size. The T'au showed no sign of stopping their aggressive expansion in the Eastern Fringe despite their losses in the Zeist Campaign.
History
By the year 997.M41, T'au expansionist activities encroached upon Imperial worlds with the initiation of the T'au Empire's Third Sphere Expansion. This expansion campaign was notable in that the T'au Empire resorted on occasion to annexing Imperial planets by military force, rather than the seemingly more common approach of cultural subversion by promulgating the doctrine of the Greater Good. By ca. 999.M41, Imperial planetary governors in the Eastern Fringe of the galaxy were calling for massive reinforcements to push back the T'au forces, but with the constant attacks on Imperial space by the Tyranid Hive Fleet Leviathan and an increase in attacks by the piratical Chaos Heretic Astartes from the Maelstrom Warp rift, few Imperial defence forces were able to respond to the call.
One Imperial defender who could, however, was the Ultramarines Chapter Master Marneus Calgar and his Space Marines. He dispatched the Ultramarines' famous 2nd Company to the Zeist Sector to draw a defensive line through which the T'au would not be able to pass. Calgar also sent requests to other nearby Space Marine Chapters for further assistance.
When the Ultramarines arrived in the Zeist Sector, they found numerous Imperial worlds abandoned to the T'au and others heavily fortified to defend against the xenos' lightning raids. Captain Cato Sicarius, commander of the Ultramarines 2nd Company, attacked the Forge World of Praetonis V to break the ongoing T'au assault on that planet and used this momentum to begin pushing the T'au offensive back. Captain Sicarius used the same tactics as the T'au, which were ideal for a relatively small force of Space Marines, including rapid lightning strikes on weak positions to destabilise more heavily defended ones. Due to the Ultramarines' efforts, the T'au expansion slowed and then stopped under the Imperial assaults. Eventually, only the world of Augura, in the Zeist Sector, remained in T'au hands, as their only remaining logistical and repair source in the area.
By this time, the Ultramarines were no longer the only Space Marine forces involved in the assault. Warriors from the Night Watch, Halo Dragons, Silver Skulls, Sable Swords, Crimson Fists, Iron Lords, Aurora Chapter, Eagle Warriors and the Knights of the Raven, as well as many others, had all joined the Ultramarines in the attack on Augura. Despite their advanced technology, battlesuits and plasma weaponry, the T'au had no hope for defeating such a large combined force of Space Marines. Augura's fortresses, shipyards and weapons factories were either badly damaged or destroyed by the Space Marines's offensive. With the loss of their last forward logistical base in the sector, the T'au appeared to fall back to protect more secure territory within their borders, apparently bringing their Third Sphere Expansion to a close.
Unfortunately, though the Space Marines had won the war and appeared to stop the T'au's seizure of Human territory, it was not possible to sanction a retaliatory thrust into T'au-held space as the individual Space Marine forces were required elsewhere in the galaxy to hold the line against the forces of Chaos during the height of the 13th Black Crusade. Reluctantly, Captain Sicarius returned control of the defence of the Zeist Sector to its individual worlds' planetary governors.
Later intelligence revealed that the T'au had anticipated the Imperial counterattack and that the Zeist Sector campaign was used as a colossal diversion, tying up the elite of the Imperial rapid response forces in a sacrificial zone to allow the T'au to launch offensives against more valuable targets in other sectors, and scythe deeply into more valuable territory. Many worlds of the Imperium toppled to this onslaught. Among the victories won by the T'au at this time was Commander Shadowsun's conquest of the strategically important Imperial world of Agrellan, which took place mere solar months after the conclusion of the Zeist Campaign. Agrellan was conquered by the T'au and renamed Mu'gulath Bay.
Space Marine Order of Battle
- Tactical Squads - Provided by the Ultramarines 2nd Company, Night Watch, Halo Dragons, Silver Skulls, Sable Swords, Crimson Fists
- Devastator Squads - Provided by the Iron Lords.
- Predator armoured spearhead - Provided by the Aurora Chapter.
- Terminator Squad - Provided by the Eagle Warriors
- 3 full companies of the Knights of the Raven
Sources
- Codex: Space Marines (5th Edition), pg. 48
- Codex: Tau Empire (6th Edition), pp. 19, 29