The Scourge of the Slave Lords was a time when the Mantis Warriors stood alone against the predations of the terrible forces ranged against the Imperial worlds near the Maelstrom's edge. In 901.M40, the worlds of the Endymion Cluster of the Maelstrom Zone were victimised by Dark Eldar reavers known as "Slave Lords." Inhumanly cruel and with the malignant patience of venomous spiders, the Eldar's dark kin were things of smoke and glass sharp shadows, impossible to find and far too cunning to easily bait. For more than sixty standard years the Slave Lords scourged the Maelstrom Zone, their blood-dark serrated ships descending on unprotected worlds, carrying off thousands screaming into the night sky, preying on ill-defended convoys and murdering isolated outposts too far from aid. After three-score Battle-Brothers of the Mantis Warriors died valiantly in a vain attempt to protect the foremost shrine-city of the Feudal World of Tranquility II from the Slave Lords' predations, the whole Chapter turned their collective will to bringing about the Slave Lords' fall.
Turning to the Mantis Warriors Librarians, to hide their actions from sight, the Chapter hatched a plan to entrap their enemies by providing them with a target too great for their vanity and appetites to ignore. Publicly vowing that Tranquility would be defended at any costs, they posted extra piquet vessels in the star system and began to gather the planet's small population in a single city-encampment, defended by two forces of Mantis Warriors, one seen and the other concealed beneath the desert sands on which the camps rested. Very soon, a series of probing raids occurred in the nearby systems, behind which the Chapters' Librarians determined a sophisticated pattern designed to tease apart a flaw in Tranquility's defences, allowing the reavers to slip though. When news came of a heavy raid on the vital void mining colonies of Sigard, the Mantis Warriors gambled that this was the grand diversionary attack they had been waiting for. Leaving a skeletal force to defend the million-plus souls now waiting fearfully in the camps, the Chapter's warships departed the system at speed.
As essentially empty Mantis Warriors Strike Cruisers giving the appearance of a full Chapter response departed the Tranquility System, seemingly from nowhere, the twisted, dagger-like forms of Dark Eldar vessels appeared in Tranquility's skies. Before them, burning black disks ripped into existence; holes in the fabric of reality from which shark-like skimmers and razor-winged skiffs poured forth to descend on the encampments, shrieking like creatures of nightmare. With hardened hearts the Mantis Warriors waited in silence as the Dark Eldar reavers committed to the attack and hundreds of refugees died screaming to slicing whisper-thin blades or were struck down in their droves by storms of hypersonic poisoned splinters. These martyrs' deaths had brought the enemy within the Chapter's grasp and their trap was sprung. From the desert sands beneath the camps the Mantis Warriors rose up in a vengeful fury to tear their foes from the skies. Elsewhere, hidden in the dune seas of the deep deserts, two Cobra-class Destroyers, buried more than seven months previously, shook off the covering shrouds of sand from their sunken prows and fired their torpedoes at point blank range into the bellies of the Dark Eldar ships high above. The torpedoes' fusion warheads, designed for space combat, burst like exploding suns above the arid land. As fire and wreckage fell from the skies, the hurricane strength blast-winds scattered the alien skimmers like dead leaves and drove sand and dust before them in walls hundreds of metres high. The Mantis Warriors' blades were wetted with alien blood in the tumult as the murderous Dark Eldar were thrown into confusion.
The surviving corsair ships, badly wounded by the surprise attack, struggled to escape Tranquility's orbit and abandoned their kin below to their fates, only to be caught and destroyed in the outer system by the returning Mantis Warriors Strike Cruisers as the last part of the Chapter's vicious trap slammed shut. The Mantis Warriors revelled in their revenge, offering no mercy to the blinded and broken enemy, many of whom died not at the hands of the Space Marines, but were brought down by mobs of desert tribesmen whose terror had been transformed into wrath. As the winds finally died away and the fires muted, thousands of human lives had been lost to the Emperor's grace, but the scourge of the Slave Lords was ended and the lives of many tens of thousands more had been saved.
- Imperial Armour Volume Ten - The Badab War - Part Two, pp. 67-68