Keeping his existence a secret save for a select few during the [[Siege of Terra]], Vulkan next saw action when [[Magnus the Red]] and a group of his [[Thousand Sons]] infiltrated the [[Imperial Dungeon]] to kill the Emperor. Vulkan blocked a lethal blow by Magnus' staff that had been intended for the Emperor's form upon the Golden Throne{{Fn|19a}}, but quickly backed down and alongside their father bid Magnus to return to the Imperial's fold. Vulkan became disheartened when Magnus refused the offer to return to the loyalists after the Emperor told him that he would have to purge his [[Space Marine Legion|Legion]] due to its rampant mutations. Vulkan himself admitted he would have made the same choice as Magnus, but nonetheless again defended the Emperor against the Crimson King's assault. Vulkan and Magnus then engaged in a furious duel, but was saved from a piercing blow thanks to the sacrifice of [[Barek Zytos]]. Horrified by his sons death and taking up his [[Thunder Hammer]], Vulkan wielded twin hammers to seemingly beat Magnus to submission. However , before a visibly despairing Vulkan could deliver the final blow Magnus fully gave himself to the powers of [[Chaos]] and vanished from the Throneroomthrone room.{{Fn|19b}}

Initially in their battle, Vulkan seemed to hit nothing but smoke and it became apparent he was swinging his hammer at smoke. The real Magnus was behind a psychic barrier, steeped with his own ritual to weaken the Emperor. Vulkan took advantage of this by smashing through the already-stressed Magnus' barrier, forcing the Crimson King to try and kill Vulkan directly so that he may be allowed to complete his work. Magnus tried every method conceivable to kill his brother. He beheaded him with his khopesh, suffocated him by turning his lungs to amber, drained him of his blood, and immolated him with psychic fire. However , nothing worked, and each time the [[Perpetual]] Vulkan would regenerate and continue to hammer away at Magnus. Attrition took hold, and Magnus grew increasingly desperate. He entered Vulkan's mind as the noble he had once been, attempting to explain his actions. Vulkan had none of it however, scolding Magnus for his arrogant and reckless use of sorcery that had turned him into a slave to Chaos. In the Webway, Vulkan stood above Magnus ready to deliver the killing blow. However , he hesitated despite the Emperor's own voice ordering the Salamanders Primarch to kill his brother. Magnus used this moment to unleash the spell he had been working on, undoing Vulkan at a genetic level in a desperate bid to finally kill him. As Vulkan crumbled apart he nonetheless was able to swing his hammer, smashing off Magnus' head with [[Urdrakule]] and banishing him into the Warp. Later, Vulkan's regenerating form was seen slowly making it back to the Palace's Webway portal, Urdrakule in hand.{{Fn|20c}}

Vulkan eventually made it back into the throne room through the Webway Gate, only to be greeted with the news that the ''[[Vengeful Spirit]]'' had lowered its [[Void Shield]]s and the Emperor Himself was preparing to lead an assault on the vessel.{{Fn|22a}} However , Vulkan was told by His father that he would not take part in this last-ditch effort, instead he would look after the [[Golden Throne]] as [[Malcador the Sigillite|Malcador]] took his place on it in the Emperor's stead. Should the traitors breach the palace, Vulkan was instructed to activate the [[Talisman of Seven Hammers]].{{Fn|22b}} Mere hours later, Vulkan met with [[Ollanius Persson]], [[John Grammaticus]], and [[Argonauts|their group]] finally reached the Palace. There, he learned from [[Actae]] of the prophecy that foretold Horus as The Dark King and the potential fifth [[Chaos God]].{{Fn|22c}}

As the Emperor battled Horus board the ''Vengeful Spirit'', the traitors advanced to within pounding on the door into the Throneroomthrone room. Thinking all hope was lost, Vulkan began to activate the Talisman of Seven Hammers as Malcador, dying upon the Golden Throne, could only watch helplessly as he knew that victory was not yet lost.{{Fn|23a}} However , Vulkan is was ultimately convinced to back down from activating the doomsday weapon after hearing the message being broadcast across Terra from [[Actae]] that the Emperor still lived and was fighting on against Horus.{{Fn|23b}} He is later present when Dorn, Valdor, and the others bring back the broken body of the Emperor and place Him upon the Golden Throne.{{Fn|23c}}

Vulkan was equipped with many finely crafted weapons built by his own hands. Most notable of these was the massive [[Thunder Hammer]] [[Dawnbringer]] and the [[Plasma Pistol]] ''[[The Furnace's Heart]]''. Before forging ''Dawnbringer'' (originally intended as a gift for [[Horus]]), Vulkan used the Hammer ''[[Thunderhead]]''. For protection he wore the Baroque baroque [[Power Armour]] known as ''[[The Draken Scale]]'', which included the [[Gauntlet of the Forge]] and [[Kesare's Mantle]].{{fn|14}} After his resurrection following the [[Battle of Nocturne]], Vulkan wielded the Hammer ''[[Urdrakule]]''. 1,500 years later during the [[War of the Beast]], Vulkan wielded the hammer [[Doomtremor]].{{Fn|11}}