|Location||Wormgyre Star System|
|Lord General Militant Slayban Bellrath||Unknown|
| 25 Million Imperial Guard
8 Space Marine Chapters
2 Titan Legions
Under the auspices of Praetor Slayban Bellrath, a powerful Terran noble and Lord General Militant of the Imperial Guard, a mighty crusade was launched to liberate the area of space designated as the Laanath Rifts, a dangerous and uncharted region located in the north-west fringes of Segmentum Pacificus. The Crusade, one of the largest in centuries, was conducted by 25 million Imperial Guard troops plus many pilgrims. The Crusade was further backed by 2 Titan Legions and 8 Space Marine Chapters. The Sons of Medusa was among the most active Space Marine forces committed to the crusade.
The ancient civilizations within the Laanah Rifts, isolated from outside human contact since the Age of Strife, provided stiff resistance to the Crusade forces. The Sons of Medusa themselves took part in fighting against a previously unknown Xenos species known as the Hellgrammite, hideous degenerate tribes, and petty human empires who denied the rule of the Emperor. Within 50 years however, the Crusade began to falter in the face of Hellgrammite resistance and their heretical bio-mechanical monstrosities.
With the Bellrath Crusade's salient routed and the horrific xenos harrowing at the retreat of the Imperial forces, the full might of the Sons of Medusa circumvented the aliens' attack fleets and conducted a perilous counter-attack, cutting behind the aliens' battle lines and thrusting at the heart of their domains in the Wormgyre Star System. Using the arcane science of their Explorator allies, the Sons of Medusa fleet had modified their vessels' Warp coils to help repel the "Aetheric Fire" that emitted from Wormgyre, providing them with a measure of defense in their attack on the Xenos realm. Knowing their time was short, the Sons of Medusa plunged directly into a headlong attack on the Hellgrammite throne-world with their full chapter strength, attacking from Drop Pods, Thunderhawks, and Assault Boats.
The relentless and merciless Sons of Medusa shattered the spider-web towers and black coral structures of the Hellgrammite, monuments raised to unknown dark gods. Caught unprepared for the assault, the Hellgrammite were helpless and massacred. Whatever resistance their fire-shapers could muster was quickly put down by the Sons of Medusa. The Sons of Medusa killed all xenos that stood before them, continuing the rampage with their bare hands long after they had run out of ammunition. The onslaught carried on until the Hellgrammite throne world had been reduced to rubble and all of its inhabitants slaughtered.
With the death of Wormgyre, Hellgrammite resistance against the crusade quickly collapsed and the race itself was quickly reduced to bands of refugees against Imperial offensives over the coming years. Within a century, a great swathe of the Laanah Rifts was brought under Imperial rule and the Sons of Medusa entered the mythology of the Sector's new settlers as the Emerald Death that fell from the stars to punish the Emperor's foes.