Butcher's Nails - World Eaters: Upon taking control of the XIIth Legion, the bloody-handed primarch enacted many changes.Knowing how successful his own cortical implants were at boosting a warrior's prowess in battle, Angron ordered his Apothecarion to insert the Butcher's Nails implants within every Astartes of the World Eaters Legion to enhance aggression and pain tolerance far beyond that which even the gene-engineered flesh of a member of the Space Marine Legions was capable.This posed difficulties, however, as Angron's implants were relics of a long-lost technology, little understood even by their makers, while removing them from Angron for close study would have proven fatal to the primarch.The Legion's Techmarines and Apothecaries attempted to duplicate the process using the primarch's own implants as templates to reverse-engineer the devices.Early attempts to duplicate these implants were far from successful, and resulted in high rates of mortality and irrecoverable homicidal frenzy on test recruits.However, as time progressed, a viable form of the cortical implant technology was replicated and steadily improved by the Dominus Nutritor and Master of Inductii Gahlan Surlak, although it was never fully stable or produced consistent effects between subjects.In the wake of the Ghenna Massacre during the Great Crusade, entire newly-formed companies of recruits were implanted, as well as large numbers of existing World Eaters who volunteered for the dangerous operation.The majority of these Astartes were absorbed back into the XIIth Legion's line units, while those deemed perhaps too unstable for such tasks joined a growing number of near-berzerker assault units known as Rampager Squads, and even within these units, those too far gone to be anything but restrained as savages between battles became known as the Caedere or the "Butchers," a frightening portent of what was soon to come for the entirety of the XIIth Legion.In those earliest days, the Butcher's Nails were considered a virtue. None of the Astartes of the newly-renamed World Eaters Legion would face the fact their primarch carried a curse from the years on his homeworld.They focused on his prowess, on the strength and speed gifted to him by the archeotech implants, and when the primarch demanded his sons lie under the Techmarines' claws and the Apothecaries' knives, few resisted the chance to share the same virtuous pain as their noble primarch.Everything changed with the hammering of the Butcher's Nails into the skulls of the Astartes of the XIIth Legion. The World Eaters, once known for their brotherhood, became known first and foremost across the nascent Imperium for their savagery and bloodlust.Reports began filtering back of excessive Legion casualties in tactic-less displays of horde warfare, and Imperial Army forces pleading for assistance from other Legions when the World Eaters were the ones to answer their call for Astartes support. Entire planets surrendered rather than face the XIIth Legion in battle, but not all who surrendered were spared the war.The Butcher's Nails dulled all other pleasures, until the heady bite of adrenaline unleashed through the stress of combat was the only certain way for a recipient of the implants to experience anything but the dimmest memory of emotion. Their rewired minds allowed no other pleasure beyond battle and slaughter.The rot had started to corrode the XIIth Legion as soon as they had rescued their primarch from his backwater world, yet the World Eaters could still have refused to receive the Nails. They chose instead to emulate their gene-father, despite all it would cost. They chose to mutilate themselves and to tear open their skulls and let the poison of the Nails be placed inside.Though Angron had ordered the implantation of the Nails, even he could not have truly forced a hundred thousand transhuman warriors to bend to his will if they had refused the mutilation of their minds. Deep in their hearts, the Legionaries of the XIIth Legion knew that Angron had been broken long before he ever reached them. That was why they had allowed him to have the Butcher's Nails implanted in their heads.The World Eaters had hoped that by breaking themselves upon the same anvil, they might finally feel unity, a sense of kinship, with their damaged gene-father. But this weakness only bred corruption, and the World Eaters eventually found themselves cursed to spend an eternity in bloody slaughter in the name of the Blood God.In the aftermath of the betrayal of the Isstvan III Atrocity, the World Eaters Legion, under their savage Primarch Angron, became ever more insular as a Legion and uncontrollable on the battlefield, proving a double-edged sword even to their allies.The psycho-surgery rife within the Legion became even more widespread and extreme in its use, and the neophytes inducted with ever-increasing pace into the World Eaters' ranks to replace the fallen were cerebrally mutilated with the Butcher's Nails implants as a matter of course.All-out infantry assaults supported by fast moving armour, with the aim of immediately closing into bloody melee with the foe, had always been a hallmark of the Legion, and now became often their goal; carnage for its own sake beyond any strategic objective to the contrary.