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Gorgon, unique for its ability to rapidly evolve its bioforms, first attacked an orbital perimeter outpost of Sha'draig in 980899.M41, then continued on to the shipyards of Sha'draig's moon. Initially the defenders sealed themselves in the main complex and trusted in the shipyard's interceptor guns to hold the invaders back, but soon an adapted strain of Gargoyle with a refractive mucous coating that lessened the damage from interceptor fire overwhelmed the shipyards and slaughtered its remaining defenders. The Kel'shan Sept fleet was sent to investigate the outpost's silence. But by the time it arrived in 420990.M41, Sha'draig was already under siege by the Tyranids. Valroth's fleet broke through the Tyranid blockade surrounding the planet long enough to deliver reinforcements to the surface.
On Sha'draig, Hormagaunts assaulted the Tau outer defence lines in the nearby forests, which Shas'el Vorcah had filled with Kroot auxiliaries directed by Shaper Pechallai. However many of the Tyranid creatures ended up entangled in the forest's undergrowth where the Kroot could easily dispatch of them. Gorgon's next wave was of new Hormagaunts adapted to be swifter and less prone to being entangled, but they were also eventually stopped by the brute force and tenacity of the Kroot. A final wave, consisting of Hormagaunts honed to pierce and tear Kroothide, ultimately swamped Pechallai's defences. The Hormagaunt's adaptions however had weakened their own resistance to injury and so when they emerged from the forests, the Tau defenders quickly gunned them down.
Gorgon's cycle of adaptation began again, and soon Hormagaunts and Termagants were deployed with close to total immunity to Pulse rifle fire. These creatures overrun the main settlement of Sha'draig, forcing Shas'el Vorcah to withdraw his forces to the mountains. The Tau, in response to the creature's resistance to their current weaponry, sent Stealth Teams to recover the Kroot rifles from Pechallai's fallen defences and distribute them amongst Vorcah's surviving Fire Warriors. The enemies responses to each other continued, with the Tau racing to develop new technology and weapons and the Tyranids breeding new biological creatures with ever more suitable adaptions. At one point Gorgon spawned Hormagaunts and Gargoyles with chameleonic hides to blend in with their surroundings, making them all but hidden to the Tau except for their Battlesuit sensors.
In 843901.M41, Supreme Admiral Kor'O'Vanan deemed the situation on Sha'draig irretrievable and ordered a withdrawal. His fleet broke through the blockade and attempted to evacuate all the surviving ground forces, but Vorcah remained behind under the guise of covering the retreat. However his true intention was to continue the fight with a series of suicide missions to break the Tyranid Synapse web, for the Tau had learnt that Gorgon's rapid adaptation was forcing it to rely on smaller, less complex organisms able to be quickly bred and so it had relatively few larger creatures. Vorcah's tactic was successful and eventually drove Gorgon from Sha'draig, but not before it had been almost completely consumed.