The Corrinos Campaign was a battle of the Great Crusade waged by the Word Bearers. Launched after the censure of the Word Bearers by the Emperor after the destruction of Monarchia, the campaign demonstrated the Legion's new zeal with the fires of treachery burning in their hearts.
Corrinos was a system of worlds that lay close to major Warp routes between the Sol System and Eastern Fringe. Initial reports indicated the population was willing to peacefully incorporate into the greater Imperium, but as the Ultramarines arrived to transition the system to Imperial rule they found its three worlds in ruins. All that remained was a lone Imperial ship lingering in orbit.
Apparently, the initial Imperial scout fleet in the system had been ambushed and obliterated after a false parlay. The account given to the Ultramarines reported that their fleet's Astropaths had broadcast a garbled message that called for help and spoke of treachery. A Word Bearers fleet under the command of Chapter Master Hasdrubal responded, racing to the System to find that the worlds of Corrinos were tainted by Psykers. These Psykers had clouded the minds of the Imperial scout fleet, seeding them with lies that would draw more victims to Corrinos. It had only been by chance that the Astropaths' desperate message had broken through. When the Word Bearers arrived they began a bombardment of the worlds of Corrinos, followed by a mass landing on the surface.
In response, surviving enemy Psykers used their powers to unleash a lightning storm on the invaders and waves of mind-slaved citizens flung themselves before the Word Bearers. However it was a futile resistance, and the Word Bearers advanced before withdrawing to orbit again and leaving the first planet of Corrinos in flames. After this episode, the Word Bearers did not bother with more landings and simply destroyed the remaining two worlds of Corrinos with orbital bombardment.
Imperial authorities believed the Word Bearers' accounts at the time, not knowing of their fall to heresy. However in reality Corrinos could have been a key mustering ground for forces from Ultramar to reinforce Terra.