The Bellrath Crusade was one of the largest of its kind in centuries, conducted between 182.M38 and 435.M38 by the Imperium to liberate and dominate the area of space designated as the Laanah Rifts in the north-western fringes of the Segmentum Pacificus. The Crusade was conducted under the auspices of Praetor Slayban Bellrath, a powerful noble from the Terran court who was raised to the rank of Lord Militant. This Crusade was conducted by well over 25 million levied Imperial Guard troops with unknown numbers of pilgrims and hangers-on swept along in its wake. The Crusade was supplemented by the forces of 2 Titan Legions and eight Space Marine Chapters at various times of which one of the most active was the Sons of Medusa. The Laanah Rifts were a dangerous and largely uncharted area of space, much of which had remained untouched by human contact since before the Age of Strife, and the Crusade met stiff resistance to its progress from the start.
Shortly after the opening thrust into the unknown, the Sons of Medusa Chapter was heavily engaged in fighting previously unknown xenos species, hideously degenerate void tribes and petty sub-human empires who denied the Emperor of Mankind's ascendancy. Within 50 standard years, the Crusade began to falter, and it was at this time against the twisted alien race given the name of "Hellgrammite" by the Imperial forces, that the Sons of Medusa would win their greatest victory of the Crusade. These foul anthropoid creatures possessed occult-infused weaponry capable of flooding the void around their worlds with Ætheric fire, and although their physical forms were decayed and frail, they rode to battle on the backs of howling bio-mechanical monstrosities whose barbed-pincers could slash through tank armour with ease.
With Bellrath's Crusade salient routed and the horrific xenos harrowing the retreating Imperial forces, the full might of the Sons of Medusa circumvented the aliens' attack fleets and conducted a perilous counterattack, cutting behind the aliens' battle lines and striking like a spear thrust at the heart of their demesnes at the star system code-named "Wormgyre." Using the arcane science of their Explorator Magos allies, the Chapter's fleet had modified their vessels' Warp-Drives to help repel the Ætheric fire that shielded Wormgyre, providing them with a measure of defence for a time, and so were able to catch their enemy complacent behind their burning skies. Knowing that time was short, the Sons of Medusa plunged directly into a headlong attack with the whole gathered might of their Chapter, hellish flames licking at their warship's Void Shields as they plunged into low orbit over the Hellgrammite throne-world to unleash their deadly waves of Drop Pods, Thunderhawks and assault rams on the alien cities.
The Sons of Medusa's attack was as relentless as it was merciless, and the Hellgrammite's spider-web towers of black coral were shattered and charnel-bedecked temples to the Dark Gods raised millennia before by inhuman hands were cast down. Caught unprepared by the speed and ferocity of the assault, the Hellgrammite for all their Warp-spawned might were as helpless as children before the storm. Such resistance as the aliens could mount was mercilessly crushed, their dreaded fire-shapers isolated and gunned down in hails of Assault Cannon fire and their mighty battlermechanoids felled by Thunder Hammer and Power Axe. It was said afterwards that the Sons of Medusa killed and killed again, methodically and coldly destroying the creatures, firing until the Promethium in their Flamers was exhausted and their last Bolt shell spent. Still they went on killing, first with Combat Knife and Chainsword, and then when they dulled and failed, with anything they could find to wield. Many Battle-Brothers were reduced to pulverising their enemies with their armoured fists and tearing the shrieking, panicked creatures apart with their bare hands. The onslaught carried on until the rubble of the alien temple-cities was painted with the Hellgrammite's pale ichors and half their world had been smashed into ruin. Only then did the Sons of Medusa withdraw.
With the death of Wormgyre, the Sons of Medusa had torn the heart from the enemy, both militarily and spiritually, and the Hellgrammites' resistance to the Crusade collapsed, their will to war broken at a stroke. In a handful of years they were no more; a once proud alien race reduced to ashen-ruins with a few scattered refugees hurling themselves into the mercy of the deep void to escape the wrath of humanity. Within a century, a great swathe of the Laanah Rifts was brought under Imperial dominion, and the Sons of Medusa entered the mythology of the new sector's inhabitants, whispered of in the old tales as "the Emerald Death" that fell from the stars to punish the God-Emperor's foes. The Chapter for its part has retained some ties to this, the site of one of their most lauded victories, maintaining infrequent contact with some of the Adeptus Mechanicus factions that founded bases on its frontiers, and holding seldom-used recruiting rights on several of its worlds in tribute to their role in the Laanah Sector's founding. The Bellrath Crusade was successfully concluded in 453.M38.
- Imperial Armour Volume Ten - The Badab War - Part Two, pp. 97-98