"This is where an age ends and an era of reformation begins. With this victory, we have secured our dominance! We have secured the gene-seed! "Do you think this is the end?" "Sadly, no. This is merely a beginning. A beginning of a war for survival. The baby is born, but it is up to us to make it live."
―Alistair Crackham and his adopted daughter Irmina Crackham, after the Conquest of Titan.
The Conquest of Titan was a major war waged by the fledgling New Imperium to capture Titan and execute the last High Lord of Terra, Captain-General Zakon Kingbane. The war lasted for approximately 5 years as the New Imperium waged a war of attrition against the loyalist forces until they were unable to resist an invasion. The war ended when Alistair Crackham led the final charge against Grey Knights' Fortress-Monastery and killed the Captain-General. The New Imperium secured the Citadel with the gene-seed stocks intact and transformed it into a Fortress-Monastery for a new chapter that would be founded after the war: the Crimson Wardens.
However, because the New Imperium decided to wage a war of attrition in order to capture Titan intact and didn't just declared an Exterminatus order, the command squad of the Grey Knights managed to escape through the help of the traitorus Iron Hands and spearheaded the formation of the Imperial Remnant in Segmentum Tempestus, which made the New Imperium earn a grand enemy.
"I leave Holy Terra to return shortly after or die trying. Which one comes first doesn't matter."
―Captain-General Zakon Kingbane, before escaping from Terra.
During the climax of the Second Battle of Terra, an Imperial fleet managed to escape the Reformist forces by taking advantage of the confusion. The reason why this fleet was then pursued by the reformist armada relentlessly was because Captain-General of the Adeptus Custodes, Zakon Kingbane, was aboard it. The fleet eventually managed to evade the reformist armada and took shelter in Titan, which was untouched by the warfare that nearly destroyed Terra. Titan welcomed the fleet and prepared for war when the news were heard.
The newly chosen Supreme Grand Master and the Captain-General prepared a defense plan to hold Titan until the reinforcements from Krieg and Segmentum Tempestus arrived. However, their plan was destroyed because the war in Terra ended sooner than expected and the New Imperium was officially founded after the reformists secured most of the planet. Zakon was one of those that saw this New Imperium as a heresy to the will of the Emperor and even he was surprised to see how many of his fellow Custodes had fallen under the influence of this heresy. Surely great purges awaited them after Terra was retaken and the heretical Lord Solar beheaded.
"Pathetic. The enemy has already withdrawn all their forces below to the planet's surface, or whatever is down there. Surely they think they can hold out longer on a ground war. I can't believe a navy in shambles can scare these traitors that much." "You're being too harsh on them. After all, almost the entirety of the navy is here, innit?"
―A recorded conversation between two Captains of the Reformist Armada.
While the forces on Titan readied themselves for war, the New Imperium was quick to realize Zakon's absence. All of the New Imperial Armada was sent to Titan, filled to the brim with soldiers to end this war before it even began. Having created a big network of spies on Segmentum Tempestus during his years as Lord Commander Militant, Alistair used all of his network and dedicated them to one thing: Preventing the reinforcements from arriving. The fleet amassed on the orbit of Titan, only to discover that the enemy had withdrawn all of their assets to the planets surface, especially around the Fortress-Monastery of the Grey Knights.
The navy was undecided what to do with this newly acquired information and was standing on halt when a small Iron Hands vessel secretly slipped through the blockade and landed on titan. Containing the representative of the Iron Council, the defenders decided to allow the vessel inside, because they knew of the Iron Hand's dark secret and wish. In the depths of the Citadel, a deal was struck and the Iron Hands departed in silence.
With the arrival of some more additional forces, a meeting was held in the flagship of the Reformist Armada, the Hyperion, and plans were laid out. In the end, it was decided that this threat should be destroyed as fast as possible and the majority agreed on an Exterminatus. The method was chosen to be by orbital assault and the navy positioned their guns accordingly, waiting for the signal.
"Soldiers! Stand tall, for today you face the enemy of our New Imperium! They are a blight on this world, corrupt to the last man and damned for eternity for they will face us! Now men, to arms! Fight on for the New Imperium! Fight on for those left behind!"
―Lord General Hakan Giray, rallying his troops for the ground assault.
However, just as the plan was about to be issued, news reached to the High Consul that a new chapter was discovered in the depths of the Imperial Palace on Crimson Terra. Bearing the gene-seed of the Grey Knights and by extent, the Emperor himself. Initial reports confirmed that the first batch of marines raised actually stood loyal to the New Imperium. This important breakthrough meant that the gene-seed of the Grey Knights could've also been exploited and used to further the New Imperial Cause. It also meant that the New Imperium was missing a remarkable opportunity here.
Calling all the Heroes of the New Imperium and the Grand Admiral of the Reformist Armada, Alistair notified them of this important development and an intense discussion followed. In the end, it was decided that the Exterminatus would be called off. No matter how hard or crazy it was, New Imperium had to get their hands on the gene-seed located in the vaults of Titan. Thus, a new strategy proposed: A war of attrition. The New Imperial forces heavily outgunned the defenders and this meant that a war of attrition was the best way to secure the Citadel. The Reformed Guard and all the Space Marine Chapters were notified of this and thus, the initial assault began three solar days later.
The first stages of the ground assault went exactly according to plan as Titan was slowly conquered by the New Imperium. Pulling all their remaining forces back into the Citadel, the defenders hunkered down and abandoned all they couldn't transport, waiting for the reinforcements from Segmentum Tempestus to arrive. The war of attrition turned into a siege and the defenders were initially able to keep the New Imperium at bay for five years. However, the reinforcements they were expecting did not arrive. Alistair's spy network had stirred so much chaos in Segmentum Tempestus that there was a visible opposition against the current Lord Commander Militant of the Region. Led by an individual known as Clovis Vecto, this opposition was tearing the navy and the army in the region into two, giving the New Imperium precious time to both continue the siege and expand into Segmentum Tempestus. Hidden from almost all of the siege force, this small piece of information was the thing that was keeping the status quo of the assault in place. However, time was running short.
Five years after the start of the ground assault, the defenders had killed at least 4 million New Imperial troopers. Driven into desperate measures, the New Imperial High Command agreed on a "Grand Plan", one final move to take the Fortress-Monastery and destroy the defenders completely. A kill team comprised of all the remaining Exorcists were sent to the Citadel, tasked with creating a breach that the New Imperium could use. To divert the attention of the defending force, High Consul Alistair Crackham and the Exorcists' Command Squad led a massive charge to the front gates, in which one million Reformed Imperial Guardsmen were sacrificed.
However, the kill team successfully entered the Citadel and managed to locate a weak point in the left wing that could be used to break through. What they found was a reactor that was positioned too close to the walls. An explosion in the area meant that even the mighty walls of the Citadel would be torn down. Fighting their way to the reactor, the Exorcists were nearly wiped out. Having been pinned down and unable to retreat, the remaining Exorcists decided to detonate themselves with the reactor, making one final and glorious stand. The following explosion did have the desired effect and the walls of the left wing were in shambles. Faking a retreat and regrouping their forces, Alistair led the assault to the Citadel. The outer courtyard fell in mere solar hours and the defenders were pushed back into the heart of the Citadel. Securing the outer courtyard, the New Imperial forces pushed on relentlessly.
"Your arrogance knows no bounds Alistair! You used to be one of us! Show some respect and help me. Give up your useless cause!" "Wicked eyes and wicked hearts deserve neither respect nor mercy. My cause is the Imperium and I will not give it up."
As the New Imperial forces marched to the heart of the Citadel, Alistair, along with Enoch Ryder and the entire Exorcists command squad, were ambushed by a force of inquisitors and Zakon Kingbane himself. Believing that the execution of Alistair would dissolve this heretical "New Imperium", Zakon had enacted a risky plan and ambushed the High Consul in the confusion. Alistair, even though he was no match for the mighty Captain-General of the Adeptus Custodes, did not back down. Without a single word, the Exorcists assaulted Zakon while Alistair, accompanied by his personal guard, lashed out at the inquisitors. The Inquisitors were slowly being dealt with whereas Zakon was busy holding the entire command squad of the Exorcists at bay. Having killed the Chief Librarian and the Squad Apothecary, Zakon was almost untouchable. After his guard was destroyed, he was planning to kill Alistair by any means necessary and he would've had his chance if the Exorcists hadn't been there.
The High Consul was merciless and reckless, killing all the inquisitors and acolytes that attacked him in a poetic manner. With a few of his men left, the High Consul stood triumphant. However, same couldn't be said for the Exorcists. Zakon, with a miraculous display of power, had wiped out all of the Command Squad and was fighting with Enoch one on one. Alistair ordered his men to advance towards their position and the soldiers quickly rushed at Zakon, who had just mortally wounded Enoch Ryder. His armor had suffered multiple breaches and The Kingbane was wounded as well, but he fought on. Killing all of Alistair's remaining personal guard, Zakon lashed out at the High Consul with the last bit of his strength.
Alistair, in that brief moment, saw Enoch trying to grab his power lance. He knew what to do. Taking a deep breath, the High Consul looked at the beast charging at him. This was it, this was the "moment of truth", in his words. Answering Zakon's first blow, Alistair parried his second and third attack, then countered his move and knocked out his helmet. Zakon quickly retaliated and punched Alistair back a few meters. Barely able to look at his foe, he saw Zakon raise his guardian spear and then closed his eyes, waiting for the end. Before this could happen, however, something pierced Zakon's throat. Enoch's power lance hit the exact location he had aimed for. Falling on his knees, the Kingbane was barely breathing whereas Enoch had already fallen.
Alistair quickly rose up and grabbed his power sword. Zakon looked at the man that once served as Lord Solar among the High Lords of Terra. Was this the fate he would meet? Was this his end? He looked at Alistair and with a final hope, he begged him to stop this madness. Alistair had nothing but a cold stare in his eyes. With a swift move, the last parts of flesh connecting Zakon's head to his shoulders were severed. Alistair did the best he could do to honor this colossus of war by granting him a swift death. The Kingbane was no more.
"Sir! The Iron Hands' Fleet broke away from the siege force and enemy units are boarding their ships. Also, the Imperator Class Titans on Titan have stopped responding. Orders?" "What?! This is treason! All batteries, open fire at them! Focus fire on the boarding ships and warn all ground forces!"
―Grand Admiral Chaka to the command personnel of Retribution, after the treachery of Iron Hands is exposed.
As the battle drew to an end, a small amount of ships managed to leave the Citadel and proceeded to leave the atmosphere. First, the Imperator-Class Titans were ordered to shoot the ships down, but contact was quickly cut and the Titans stopped responding. Later on, when the ships managed to evade the New Imperial assaults and left the atmosphere, the New Imperial blockade was preparing to open fire. Unexpectedly, the Iron Hands' flagship, Battle Barge Iron Hand, proceeded to shield the small escape shuttles and the entire Iron Hands fleet opened fire on their once allies, sealing their betrayal. As the remnants of the defenders entered the Iron Hand, the entire fleet pulled back, taking advantage of the mass confusion it caused with their betrayal. At the very same time, the Imperator-Class Titans positioned in Titan opened fire on the New Imperial forces on the planet, causing mass confusion inside the ground troops once again.
The confusion was so widespread that High Consul Alistair Crackham had to spearhead an advance towards one of the towers of the Citadel and, thanks to the aid of his adopted daughter Irmina Crackham alongside a reformist Imperial Fists squad, managed to capture the tower entirely. He then proceeded to display Zakon's head on top of the tower while all the reformists that rallied around him almost literally turned into meat shields, trying to protect their High Consul. This simple but brave heroic broke the defender's morale entirely and what was left to delay the New Imperium were utterly scattered. With the chain of command reestablished, the High Consul was forced to depart Titan, making way towards Crimson Terra to assume his bureaucratic position and ensure that the laws and regulations of the New Imperium were implemented accordingly. However, despite all efforts, the betrayal of the Iron Hands and all the Imperator-Class Titans left a deep scar in the New Imperium, one that hasn't fully healed even to date.