Broken, The - Assault on the Blood Keep: Four maniples of Kastelan Battle-automata to the front, the Renegade Mechanicus forces entered the central chamber -- locally referred to as "The Skull Chamber" -- and fanned out. Arrayed against them, the hordes of Chaos brayed their anger.They were mostly Chaos Cultists, the cannon-fodder of the Dark Gods' armies, but at their head their champions, the Renegade Space Marines of the Broken, held the foe at bay. Still hidden, Inquisitor Drake's small party observed as both sides faced each other.The Ultramarines emerged as well, lead by Marneus Calgar and the towering form of Sergeant Starn's Terminators. The hard march through the Fury’s interior had cost the Astartes dearly and only sixty Space Marines remained ready for the fight. The Ultramarines deployed on the advance's left flank, adopting a checkerboard formation, Tactical Squads at the front and Devastator Squads at the rear.At the sight of the crucified Viridian Consuls, shouts of anger and cries of outrage erupted from the Ultramarines' line. Anger filled Calgar's twin hearts, a wrath of the kind he didn't knew he could still feel. "Taste the anger. Savour it. Feel the thrill of rage..." whispered a voice in his head, but the Chapter Master quickly silenced it with his iron will.He called out to his brothers to stand fast and ignore the dark whispers filling their heads. Calgar's piercing eyes easily located the postern gate Inquisitor Drake had first detected and the Chapter Master personally briefed Captain Galenus on his part in the battle to come.As soon as the battlelines were drawn, the Chaos horde surged forward. As they ran at their enemies, the Khornate worshipers brayed their obscene slogans and their hate of their enemy. The Renegade Mechanicus line held their position, discharging their weapons at the approaching mass of warriors. Fully half of the Chaos force disappeared in the actinic blue-white glow of electric discharge, but the remainder continued to advance.Without sparing their crucified former brothers a single glance, the Renegade Space Marines of the Broken urged their followers on and returned fire with their desecrated Bolters. Sporadic Bolter fire claimed the lives of a few Skitarii, but ultimately made little dent in the Mechanicus' line.Where the Magos Dominus' forces stood their ground, the Ultramarines chose to advance. Staying true to their initial battle plan, the Ultramarines adopted an echelon formation and redeployed on the Renegade Mechanicus' left flank. The Devastators of the 9th Company unleashed a volley from their heavy weapons. Seconds later, the Tactical Squads of 5th Company -- led by their captain -- clashed with the enemy.After a brief hand-to-hand combat where the Ultramarines proved their undeniable superiority over their merely mortal opponents, the first wave of the enemy's advance was broken. They had not even made it to within a hundred Terran yards of the Mechanicus-line. But the second wave was already in-bound, and this one was far more numerous and better organised.The second wave's mortal warriors wore defiled suits of military-issued Carapace Armour and carried more long-range weapons than the first. These troops still possessed the remnants of their Astra Militarum training, as they were disciplined enough to advance in sections. As each section moved forward, the others laid down coordinated suppressive fire.Where the first wave of attackers had been composed entirely of normal humans, this one included slathering Chaos Spawn, other mutant beasts, and even daemons. Rushing ahead of their support troops, a trio of Bloodletters mounted on fire-breathing Juggernauts advanced with murderous intent. At three hundred yards from the Ultramarines' and Mechanicus' position, the human soldiers halted and allowed the Daemons and mutants to rush the enemy lines and absorb most of the Mechanicus' fire.With savage glee, the trio of Bloodletters entered the fray, cleaving wildly with their Hellblades. Each of their swings felled several Skitarii. One of the Bloodletters was engaged by a towering Kastelan, the robot seeming to hold its own against the minion of the Blood God. With the Mechanicus' line disrupted, the Khornate Renegades unleashed their own charge.The success of their charge had taken the Khornates by surprise, leaving the Ultramarines unengaged. While the enemy was shifting its line to compensate, Magos Dominus Hagnon-Cro urgently contacted Marneus Calgar, bidding him to engage the enemy unless his own forces were overwhelmed. Seeing an opportunity to put his plan into action, Calgar passed battlefield control to Captain Galenus.With the Terminators still in reserve and his own Honour Guard at his side, Calgar slipped away while the 5th Company drew the enemy's attention. Activating the interconnection of their targeting reticules -- so that no two Space Marines would pick the same target -- Captain Galenus deployed his warriors in echelon-formation, maximising their field of fire.Since the days of Guilliman, discipline and organisational skills had been the hallmarks of the XIIIth Legion. Now, this discipline was used to bleed the enemy. Short, controlled bursts of bolter-fire hammered into the Khornate line, mowing down Traitor Guard troopers like wheat before the scythe. Every shot taken resulted in a kill. Not a single bolt was wasted. Wherever an enemy officer was spotted, coordinated heavy weapons' fire from the Devastators annihilated their Command Squad or cracked open the Power Armour of Aspiring Champions.With pin-point accuracy, a missile from a portable Missile Launcher unseated a Bloodletter, the minor Daemon vanishing in a great explosion. To conserve their ammunition, the Ultramarines favored single shots or three-round bursts, and even with this restraint, after the first two volleys they had turned the enemy line into a mire of steaming blood and ripped-off body parts.Despite the losses they had inflicted upon the enemy, the foot-soldiers of the Broken still outnumbered the Ultramarines at least ten to one. The slaughter on their right flank also diminished the pressure directed against the Renegade Mechanicus. From his position in the rear of the Ultramarines' formation, Marneus Calgar saw Hagnon-Cro himself wading into the fight, smashing the skull of a Bloodletter with his energised staff of office. Only four Kastelan-class Robots still stood tall, but their efforts were enough to hold the line.As the enemy's numbers dwindled, the Mechanicus' line reorganised itself. Having slaughtered all who faced them, the Ultramarines were free to take stock of the ammunition they had expended and count their wounded. First Sergeant Greynius went from squad to squad, compiling a report for his captain. None of the Ultramarines had fallen and only a few nursed minor wounds. Just as the fighting was ebbing down, the great gates of the Blood Keep opened again and a second army, even vaster than the first one stepped onto the battlefield.