He fought at Sha'draig, the first Tau colony world invaded by Gorgon, and eventually deemed the situation irretrievable in 843901.M41 and ordered a withdrawal. His fleet broke through the blockade and attempted to evacuate all the surviving ground forces, but Shas'el Vorcah remained behind and launched a series of suicide missions that eventually drove Gorgon from Sha'draig, but not before it was almost completely consumed by Ripper swarms.
Kor'O'Vanan engaged Gorgon at the Battle of Sol'ai Rift as it left the Ka'mais system in 550902.M41. At first things favoured the Tau, until a cluster of Ramsmiter and Razorfiend bio-ships appeared with nigh-immunity to the Tau's Ion weaponry and the Tau fleet had to withdraw. The Tau however managed to take out many of Gorgon's Narvhals, bio-ships which the Tyranids use to travel faster than light, hoping to buy time for the Kel'shan Sept to further fortify against the coming Hive Fleet.
Gorgon was finally defeated on Kel'shan. However, three Hive Ships fled towards the edge of the Galaxy and Kor'O'Vanan ordered his fleet to pursue. He caught and engaged them at Delmarra, where he managed to destroy one, though the Custodian Carrier Firestar was lured into Delmarra's asteroid belt and irreparably damaged. The two remaining Hive Ships continued to flee and Kor'O'Vanan pursued, erroneously believing that these surviving ships had to make contact with other Tyranids to transfer knowledge of how to combat the Tau back to the Tyranid Hive Mind and that the future of the Tau now lay in his hands.