Battle of Macragge - Cold Steel Ridge: For a time, Calgar's forces successfully slowed the initial land invasion of the Tyranids, trading territory for time as they whittled down the oncoming swarm. Yet even under Marneus Calgar's legendary leadership, such delaying measures would only delay the inevitable. Withdrawing further north, Genestealers burst from the sewers beneath the Sirocco Starport, slaughtering Macragge's defenders and pilots before they were brought down by vengeful Bolter fire. Much of Calgar's shuttle fleet had been taken out in one fell swoop. Though the Master of Macragge still had access to sufficient Thunderhawk gunships to supply and manoeuvre his Ultramarines, he did not possess the Auxilia forces that made up the bulk of his defence forces. With options running out, Calgar made a fateful decision to make his stand at Cold Steel Ridge.Having clashed with Calgar's army numerous times, the Hive Mind had learnt much from Calgar and the tactics that he employed. Having identified the Chapter Master as the main threat to the Tyranid advance, the Hive Mind created and despatched the deadly Tyranid bioform later classified in Imperial records as the Swarmlord. The Swarmlord was the monster who led the final assaults on Tyran and Thandros, honing strategies of encirclement and misdirection against their human opponents.Those same strategies were employed against Calgar's position on Cold Steel Ridge. Up to this point in the siege, the defenders had become accustomed to the near-mindless tactics of the rampaging swarm, but under the influence of the Swarmlord, the Tyranids' primal fury was coupled with keen strategy. The Swarmlord's ploy resulted in the deaths of dozens of Battle-Brothers. On the eastern flank, Calgar watched grimly as the Swarmlord's plans unfolded. As he led the counter assault against a Carnifex brood, Calgar recognised the malevolent intelligence within the creature, quickly realising that his enemy was not the mindless swarm it had first seemed to be.With the foe reeling, the Swarmlord extended its will and ten thousand alien minds answered. Raveners and Trygons burst from the chill ground in the midst of manned trenches, separating the beleaguered defenders from Calgar's main force. By the time the Ultramarines cut through the subterranean swarms, the trench network was a charnel of gore overrun with Tyranids. The Ultramarines purged them with fire, but in so doing left the Swarmlord's true target -- the mighty Baneblade Pride of Hera -- without infantry support. A wave of Carnifexes tore the super-heavy tank apart. With its destruction, the Imperials' western flank was lost.Over the next few solar hours, the full depth of the monster's battleplan became apparent as hundreds of Auxilia troops were killed in the most gruesome ways imaginable, as the Swarmlord employed wave after wave of the various Tyranid bioforms at its disposal. Calgar and his Ultramarines fought tirelessly, in an attempt to bolster the weakened sections of their battle line as only an Astartes could, reacting to each new threat with valour. But they were outnumbered and outmatched. Under the direction of the nefarious Swarmlord, the swarm was able to adapt to defeat Calgar's tactics as quickly as the Chapter Master developed them. Then suddenly, the Swarmlord bellowed a challenge to the human commander. Leading a bodyguard of Tyrant Guard and Tyranid Warriors, the monstrous Hive Tyrant plunged into the fray.Seeing their Chapter Master beset, the Ultramarines hastened to their lord's aid, but soon found themselves assailed from an unexpected quarter. Not all of the Hormagaunts on their left flank were lifeless corpses, for some of the creatures had been lying dormant amongst the corpses of their kin, their ravenous instincts suppressed by the Swarmlord's will. As the Swarmlord charged the Master of Macragge, the Hormagaunts were released from their slumber to fall upon the Ultramarines with fury. Though their number was not great enough to do more than delay the Ultramarines, that delay could prove costly. Calgar was laid low, his body rent and torn. Fortunately, his Honour Guard fought before their wounded Chapter Master, their Axes of Ultramar driving the Swarmlord back from the body of their fallen lord.Too late, the Thunderhawk gunships arrived from the orbiting Battle Barge Octavius, their first pass blasting the swarm back from the ridge to allow three of their number to land amongst the packed bodies of the dead and retrieve survivors. The Honour Guard was only able to get Calgar to safety due to the valiant sacrifice of Brother Aloysius, Commander of the Guard, who held his ground alone against the Swarmlord and his Tyrant Guard. Yet, as Aloysius fell, the Thunderhawks were able to lift off, carrying the few dozen survivors to safety. Because of the Ultramarines' noble sacrifice, Marneus Calgar would live to fight again, but the army of Utramar was no more. The polar fortresses were now on their own.