The Cerberus Insurrection was a conflict involving the forces of the Imperium and the renegade prisoners of the Cerberus prison colony, bolstered by ancient super-soldiers. It is noted as the only time Space Marine and Thunder Warrior forces have ever engaged in battle.
The brutal War Hounds, who would go on to become the infamous World Eaters, were tasked alongside the Terran XXIInd Dracos Regiment of the Imperial Army to subdue the asteroid prison colony of Cerberus that had risen up in anarchic revolt in a state of near continuous rioting and mob violence. Initial attempts to impose order by Terran troops had been thrown back in disarray as it became apparent that among the insurrectionists was a renegade cadre of outlawed Thunder Warriors, long believed dead, calling themselves the Dait'Tar. With many of the Space Marine Legions already assigned to the first Expeditionary Fleets of the Great Crusade and en route to the stars, the Emperor Himself dispatched His War Hounds to Cerberus with explicit instructions to reclaim Cerberus colony and carry the Emperor's wrath to those that had defied Him.
The War Hounds slaughtered all prisoners, but their confidence would soon be shaken when they encountered the Dait'Tar, despite being greatly outnumbered by Astartes and Guardsmen, the Thunder Warriors held their ground, fighting amongst the bleak tunnels of Cerberus. Eventually, after five hours of brutal close quarters fighting, a signal was received that Cerberus-Primary had been returned to Imperial Compliance. The second wave of Imperial Army troops were ordered with the bleak task of clear-up operations in the wake of the War Hounds' assault, hunting down any survivors hiding in the warren of tunnels and passageways, of which there proved to be precious few. There were multiple reports of coming across the hulking carcasses of Thunder Warriors, each with four to five Space Marines dead around them, of rooms being turned into blood soaked charnel houses and prisoners weapons being found abandoned. Aside from these facts much else remains a mystery and the entire insurrection is kept highly secret by the Imperium.