Battle of Drooth II
Tiring of trying to bring the loyalist Mechanicum fleet to battle and intending to corner the Legio Praesagius under Dae Vergos, Legio Infernus Princeps Horgoth Nyr sought to drive his rival out. Slaughtering the population of several worlds on the eastern edge of Ultramar, Nyr left a trail of breadcrumbs to the arid world of Drooth II. Vergos followed the wake of this slaughter, well aware that Nyr was baiting her but willing to risk everything for a chance to destroy the Traitor Princeps. So it was that the Loyalists arrived in the Drooth System. The planets unique mineral make-up and radiation prevented effective auger scans of orbital bombardment, so Vergos made a landing 600km from the outpost of Helgarn's Furnace which was connected to a massive geo-orbital station by a space elevator. Macrocannon and lance batteries defended all approaches to the outpost, their landed shielded by the curvature of the planet. Similar landings took place around the outpost by allied Legio Lysanda and Legio Oberon Titans as well as by several Psi-Titans of the Ordo Sinister.
As the loyalists crossed the horizon some 20km from the outposts outermost defenses, the two sides began to exchange fire as Vergos' forces came under fire from the Legio Infernus, Legio Audax and Legio Mordaxis. The loyalists under Vergos herself were nonetheless able to advance to the Helgarn Forge-fan at the base of the space elevator. As dozens of Titans engaged one another the traitors were driven back step by step. With a blood-chilling howl across the Vox half a dozen Traitor Titans were overcome with madness and unnatural speed and engaged upon the loyalists. However the loyalists were prepared, and the Psi-Titans of the Ordo Sinister were unleashed. In a vicious battle the Psi-Titan Occedentalis-Chirion was torn apart by cannibal Titans, tearing apart the boundary between the Materium and Immaterium. Through this carnage Vergos charged forward in her Warlord Titan Pride of Konor, engaging Nyr's Warbringer Titan Mons Ingnum. During the terrible duel that followed Nyr's Titan displayed unnatural endurance, forcing Vergos to overload her reactor to fire her Volcano Cannon directly into the Mons Ingnum's faceplate. However, Nyr's Engine nonetheless sprang back to life as his Titan was overcome by its tormented Machine Spirit. Knowing she could not take down the enemy, Vergos instead turned her fire on the forge-fane and magnetic locks holding the space elevator in place. The Space Elevator collapsed in on itself, crashing down on the battling armies below. Both Vergos and Nyr were killed in the catastrophe.
Though the Horus Heresy continued to rage, the Crusade of Iron came to an end on Drooth II. Whatever rage that had driven the Praesagius and their allies to pursue the traitors died with Vergos, and the loyalists withdrew back to Gantz to lick their wounds. The traitors meanwhile were broken by the loss of Nyr and fell deeper under the sway of Horus' dark influence.