Schism of Mars - Forlorn Hope: For those still loyal to the Emperor on the Red Planet, their salvation arrived in the form of a great Imperial expeditionary fleet. Malcador the Sigillite, the Regent of Terra, charged Rogal Dorn, the Primarch of the Imperial Fists Legion and the Castellan of Terra, with a mission of the most vital importance -- to secure the forges of Mars for the Imperial war effort. Dorn informed the Sigillite that he would send his Legion's Champion and First Captain Sigismund, 4 companies of Imperial Fists and a large force of Imperial Army soldiers to secure the forges of Mars.Across the northern hemisphere of the Red Planet lay an arc of Loyalist control -- the important munitions manufactoria of Mondus Gamma and Mondus Occulum. Within these two vast industrial complexes the Mechanicum fabricated the weaponry and Power Armour for the Legions of the Space Marines. The forges of Mondus Occulum and Mondus Gamma alone produced the bulk of the armour and weapons of the Legiones Astartes. Dorn intended for his force to strike there to capture those forges and once they were occupied, the Imperial Fists and their allies would push outwards and secure the others.Sigismund's companies landed at Mondus Occulum as the rest of the Imperial expeditionary force was fighting all across the surface of Mars. After a rapid deployment under fire in the shadow of the caldera of the great volcano Pavonis Mons, 13 companies of the Imperial Army's Saturnine Hoplites advanced on the Traitors' lines surrounding the forge of Ipluvien Maximal. Further south, 2 companies of Imperial Fists and 4 regiments of Jovian Grenadiers (nearly 15,000 Imperial Army soldiers in total) under the command of the Imperial Fists' Captain Camba-Diaz made planetfall in the Mondus Gamma forge complex.Unfortunately, nothing of the Imperial Fists' mission to Mars went as expected. Camba-Diaz and the Jovian regiments soon became embroiled in a fight for their lives at Mondus Gamma forge, and the Saturnine Hoplite companies tasked with breaking the siege at Ipluvien Maximal's forge were repeatedly turned back by the horrifyingly altered weapon-creatures of the Dark Mechanicum.Though the fighting was desperate, Camba-Diaz eventually secured the Power Armour forges and the ammunition silos, but his company was outnumbered a hundred to one. The Traitor Magos Lukas Chrom's troops pushed Camba-Diaz's Imperial Fists back to the landing fields and his losses proved grievous. Sigismund soon grasped that the Imperial expeditionary force would not be able to hold the forge as planned, but a great deal of essential supplies had still been secured for transit to Terra.Sigismund's companies had descended upon Mondus Occulum not knowing whether they would have to fight to secure the forge, but it was a relief to discover that Fabricator-Locum Zagreus Kane still held true to the Imperium. Sigismund secured vast quantities of munitions for transport back to Terra, including nearly 12,000 suits of Mark IV Maximus Power Armour and twice as many Astartes weapons.But the Loyalists had finally run out of time. Despite the Locum's Servitors working at full capacity, it still was not rapid enough, for Sigismund's voidship masters informed him of a sizable enemy force closing in on Mondus Occulum, composed of infantry, armoured vehicles, Skitarii and at least two Traitor Titan Legions comprising nearly 60 god-engines in all.Sigismund's desire to wreak a bloody vengeance on the heads of those who had rebelled against the Emperor warred with the necessity of the mission his Primarch had given him to secure the vital armour and weapons of Kane's forge that would be needed to defend the Imperial Palace at a later date. Reluctantly he knew he must stay true to his mission, for the forces arrayed against the Imperial strike force were simply too many and his orders did not allow for the pursuit of futile gestures of defiance. Fabricator-Locum Kane warned the Imperial Fists' First Captain that if both the Mondus Occulum and Mondus Gamma forges fell, the Imperium would have no way of replenishing the combat losses the Loyalists sustained in any meaningful way.After barely a few solar hours worth of fighting both Mondus Occulum and Mondus Gamma were burning, with great swathes of their industrial machinery and manufacturing capacity destroyed. The loss of such irreplaceable technology and knowledge for all time would be felt by the Imperium for many millennia to come.Then like comets launching from the surface of Mars, the Imperial landing ships fled for the heavens and their mother ships in orbit. Astartes and Imperial Army vessels jostled in the sky in their haste to depart the Red Planet.Barely a thousand Loyalist warriors were able to escape from the planet's surface before the manufactoria fell into the hands of the Traitors. The desperate rearguard action of the Astartes and other Loyalists on Mars and the sacrifice of many thousands of lives at least had secured tens of thousands of suits of newly-fabricated Mark IV, Mark V and Mark VI Space Marine Power Armour and other vital materiel that would ultimately prove to be the edge the forces of the Imperium needed in the campaign against the Traitor Legions of Horus Lupercal.In the aftermath of the battle for Mars, Imperial forces from Terra blockaded the planet, leading to several attempts by the Traitors of Mars to breakout. The Loyalist containment of Mars was overseen by Imperial Fists commander Efried. Ultimately, Mars would remain under the control of the Dark Mechanicum until after the Battle of Terra when the Great Scouring would ultimately drive all of the Traitor forces into refuge within the Eye of Terror.Across the galaxy, open rebellion erupted as Space Marine Legion fought Space Marine Legion and Titans battled Titans. The traitorous members of what became known as the Dark Mechanicum continued to support Horus at the start of the war later called the Horus Heresy, participating in the horrendous attacks against the Loyalist Space Marine Legions during the Drop Site Massacre on Istvaan V.Throughout the period of the Heresy they would use dark and forbidden knowledge drawn from the inexhaustible well of Chaos to help destroy the Loyalist forces. Having forsaken the Omnissiah their destinies would be dominated by far darker and more capricious gods.