The bloody battle of St.Owen's Basilica, which developed on 1209.007M42 signalled the end of Imperial resistance in Gulan and on Cerberex as a whole. General Kluge, in command of Army Group East, had held on tenaciously to the city despite numerous assaults since the first day of the Chaos invasion. The city was a thorn in Moonface's side and lack of progress in taking it had frustrated the Chaos general.
By 09.007M42 Moonface realised that with the rapid expansion of UFP controlled land coupled with the arrival of the UFP fleet, the capture of the planet's second major city had become the priority, and he diverted several legions from the war in the south to attack the Imperial stronghold. Led by Newo the Slaughterer the Chaos armies once again launched themselves against the forces defending Gulan. Well dug in and expecting attack the initial Chaos assault was a slaughteras tens of thousands of cultists died running at the Imperial trenches. However this was a diversion. A bloody one, but a diversion none-the-less. Moonface had identified the Basilica of St. Owen, on the west of the city, as a key strategic strongpoint. If it were taken the forces of Chaos could disable the cities defence shield and would also have access to a number of missile silos. The results would be disasterous.
It took Kluge almost a day to realise that he was being outflanked and by the time the first reinforcements arrived the Chaos vanguard had reached the Basilica.
Meanwhile Kluge withdrew, allowing Chaos to take the remains of the city of Gulan. It was a devastating blow to the Imperium. Even so Newo the Slaughterer had lost many men taking the Basilica, including all but one of the squad of terminators he had been assigned. The damage was enough to earn Moonface's contempt, rather than his praise.
The city of Gulan had held out since the initial invasion, despite hardships and crumbling defences the defenders had stood firm. Now that the city was lost the Imperial government moved again, this time to Grasx. The mood in the Imperial high command was at an all time low, with forces on the retreat on all fronts. Nowhere had their been an Imperial victory in the last month and it seemed like only a matter of time before the city of Grasx fell.
Imperial logisticians actually estimated it would take the UFP no more than three weeks to take the final Imperial city based on current fuel and ammunition stocks. With the loss of the Imperial fleet in the Aleph subsector, there would be no mass evacuation either.
Secretly, and without the approval of the high command, certain factions began negotiations with the UFP, particularly those under the command of the embattled Army Group South. General Von Paulus was particularly anxious to end the slaughter and on 2409.007M42 he found himself surrounded by the Hartak 8th legion. Despite orders to the contrary, he and Army Group South surrendered to the UFP on 2509.007M42, handing 400,000 troops and their equipment over to the UFP.
This also led to the swift collapse of the southern defensive line and before the day was out the logisticians had proved that the loss would inevitably hasten the end for the Imperial forces on Cerberex. In a desperate attempt to make his lines shorter Lord General Voss pulled Army Group North under Von Schlieffen and Army Group Centre under Model back some thousand miles towards the UFP front lines. This led to Model’s army becoming trapped between the planet's two seas, and only a brilliant escape plan saved his forces. Meanwhile the Great Villain Plain fell to the enemy forces who met roughly half way between the two great seas of Cerberex.
The Vennetta Heights fell next as UFP and Chaos forces closed the door on General Guderain’s Army Group West. This time there was no escape and his armies were wiped out, chiefly by Chaos forces while the UFP desperately tried to negotiate a surrender.
By 1610.007M42 the Imperial sector had shrunk to a tiny stronghold around Grasx and to the north. To the west Model fought tenaciously against the Chaos hordes while in the South the UFP gained on average 20 miles a day.
Meanwhile the Imperial forces ran short of food, water, oil and ammunition. On 2310.007M42 Govenor and Monarch Iyanen Serbellant ended the madness. He surrendered all his forces to the UFP high command. This effectively left General Voss with just a few thousand loyal Imperial Guard. A few units fought on vainly and were destroyed but most also surrendered to the UFP. Some collapsed completely, their coherency destroyed.
Following the final surrender of the Imperium on Cerberex there was heering on Tallax and Hartak as UFP units entered Grasx. There was no cheering within they populous of the city however as the fiercely loyal citizens looked on in despair as Squat Land Raiders and Tallaxian vehicles rumbled through the streets followed by thousands of jubilant worker peasants who saw the UFP as their saviours.
The UFP then braced itself for the onslaught of Chaos. They fully expected an all out assault on the now extended UFP lines. But it never came. Something odd was going on in the Chaos sector. UFP intelligence reported the Chaos forces digging in, constructing vast trench lines behind their front lines. Building bunkers, minefields and defences up to three hundred miles deep, denying the UFP their mobile battle. But they did not attack.
The Catechism leaves
In fact the Chaos forces, having defeated the Imperium on Cerberex, at least in part, had achieved their objectives. The Chaos overlord, Moonface, had uccessfully invaded the Imperial capital, something other warlords said could not be done. He had proved his worthiness and consolidated his hold over the Chaos forces in the sector. Further loss of life, or rather further loss of his war assets, would serve no purpose. The newly created Moonface Catechism began preparing to leave the planet, planning their next campaign of conquest.
This must have come as a bitter disappointment to those who had rebelled on Cerberex or had designs on a new order on the planet. Now their chief sponsor and provider was leaving, taking his best troops with him and leaving the remaining Chaos forces facing the UFP with old beaten up equipment. Many thought the UFP would quickly overwhelm them.
Then emerged a new leader, known only as Ashurman the Wise. No-one knows where he came from but he soon proved to be a canny and knowledgeable strategist. Identifying that the Chaos forces still had numbers and ammunition, even if they were lacking in ability and equipment, the wizened old Chaos Warlock made plans for the defence of the newly created Chaos Realm on Cerberex.
It was Ashurman who instigated the construction of the defences, reasoning that the UFPâ€™s greatest asset was mobility. Take that away and they would be forced to enter into attritional warfare. Something the UFP were never inclined to do. While the Catechism left by an assembled warfleet the UFP didn't dare to challenge, Ashurman had ensured that the war on Cerberex would continue for several years, if not decades.
Stand Off in the Trenches
The UFP allowed the Catechism to leave. Intelligence suggested they were leaving the Aleph subsector so there was no need to intervene. On the planet the UFP general staff looked carefully at the new data in front of them. Many days of arguing and debating finally concluded that no strategy could win the planet quickly without an abhorrent cost in UFP lives. The war would go on, but slowly.
The UFP noe controlled the capital and the space around the planet. The subsector was now firmly closed to the Imperium and Federal Space was established on 2610.007M42. A new Empire was finally born. On Cerberex itself the border between the New Chaos Realm, as styled by Ashurman, and New Cerberex, as named by the UFP, became a no mans land where no-one ventured. Occasionally both sides would launch limited assaults on each other, airstrikes or limited offensives, but neither side could wear the other down. In the following years the planet would become more like a military training ground for the UFP, a live fire exersize area where new pilots and troopers could learn their trade.