Battle for the Nerio System

Overview
In the closing months of M41 the forces of Chaos congregated galaxy wide in numbers only seen previously since the days of Horus's Heresy. From all dark corners of the galaxy they came with blades in hand aimed at the worlds of the Imperium. As countless other systems were beset so too was the Nerio system. The small, unassuming star system had once before been attacked by the forces of darkness and, keeping with the promises made by those long routed heretics, the evil returned to do battle.

Leading the assault was the warband known as the Crusaders Once Crossed. Alongside them stood scores of other traitor marines, legions of slave-soldiers, countless mercenaries, and hordes of daemons. From all corners of the system the servants of ruination crept into realspace. Upon entry the chaos fleet had no hesitation and immediately began the assault by launching tarnished, ruined space hulk filled with explosives from stern to bow straight into the site of their previous failure. The Imperial forces were caught by surprise by this assault and were initially in a state of disarray. The local space marine chapter, the Tempered Souls, moved to intercept the chaos fleet and engaged in ship to ship combat for the initial part of the invasion. After the brief naval combat the fight shifted to the brutal land battles that took place on the four planets of the system. For some time the Imperial forces within the system had to fight without any reinforcements and were very much on the defensive. It was shortly after the events on Necro that an Imperial fleet consisting of many servants of the Emperor was able to assist their brethren. After the influx of Imperial forces the battle, after much turmoil, swayed to the favor of the Emperor's people.

Syprios
The simple Agri-World of Syprios was the first to find the hellish invaders on its lands. The local PDF, the Syprios Militia, tried to man their trusty defensive installations but quickly discovered the preemptive bombardment from the marauders had rendered their planetary weapons useless. The fighting quickly became quite dire as the PDF found themselves unable to repel the enemy via their traditional methods. To make matters worse, the defenders were forced to expend a great deal of resources securing the impact site of the bomb ship to to a great deal of intact munitions which couldn't be allowed to be recovered and detonated by the enemy forces.

(battles set during the early part of the invasion go here - light fighting, pillaging)

The fighting grew quite vicious with each side facing severe losses without seeing much progress as far as taking or regaining ground is concerned. The once lush countryside fields and plains were sullied and burnt. What were once manors of nobles became encampments for mutants and cultists. The Syprian cities were arguably worse places to live than the encampments of the heretics as the besieged urban centers became filled with filth and the stench of rotting corpses. Already the world was marred and its people weary yet the battle would not soon be over.

(mid invasion - trench warfare, cities sieged, heavy losses in combat, lots of Imperial deaths from famine)

As the invasion turned against the favor of the servants of Chaos the more savage they grew. Many thousands of cultists were abandoned as their Astartes overlords fled and the same could be said for many traitor marines who found themselves left to hang by their comrades. The remaining PDF soldiers made a final assault against the remnants of the invaders in an all or nothing move. Though the heaviest fighting was at the long contested crash site the entire world was awash in blood during the final confrontation between the defenders and the marauders.

(late invasion - extreme losses, cities in ruin\many abandoned or overrun, many raiders loot and ditch)

Kri-os
The prison world of Kri-os was a excellent target for the invaders. Hundreds of thousands of killers and reavers were imprisoned on the Death World defended by a paltry amount of hired guards. A great number of Chaos craft landed on the irradiated sands of Kri-os to supplement their ranks and join in the slaughter of the guards. Much to the invaders' delight a detachment of loyalist marines was garrisoned on the world to attempt to halt the traitor's advance. The guards stationed at each of the four prisons could do little to stop their attackers and many fled to the Citadel.

(Southpoint overran in mere hours, guards slaughtered, space marine detachment routed)

All the prisons were now the domains of the invading hordes and the remaining loyalist Astartes and guards were cooped up in the Citadel. In a near constant series of assaults the Imperial forces in the Citadel were being whittled down. If the Citadel was any less hardy of a fortress the defenders would have surely perished.

(Not much progress for either side)

With the tide turned on Necro thousands of chaos warriors came to Kri-os hoping to regain the initiative by forcing the Imperial forces to attempt storming the prison fortresses. Initially this proved a fruitful tactic as the counter attacking Imperials were forced to attempt grueling siege warfare but the cowardice of a certain disciple of Slaanesh foiled the chaos warriors' defense. Those still surviving in the Citadel emerged to assist in the counter attack.

(kinda like what happened on Syprios - leaders of warbands flee leaving the peons to fight\die, big losses for both sides)

Corbonis
The temperate world of Corbonis was in turmoil even before the landing craft of the marauders reached their land. From their very cities cultists drew forth from the shadows preying upon their colleagues with utmost savagery. The mobs of cultists destroyed segments of the local infrastructure and claimed many cities as landing positions for their yet to arrive dark brethren. The local PDF was caught by surprise at the traitorous acts of their one time friends and, in some cases, family. The initial city-fighting was costly for the Corbonis PDF who were much more accustomed to fighting in the expansive woodlands spanning all over the planet.

(Loosely organized mobs doing petty attacks on PDF convoys but mostly sticking to destroying roads, power plants, manufacturing centers, etc. Conquered cities ransacked and the civilians either flee or get slaughtered)

While the initial firefights between the PDF and cult forces were costly they paled in comparison to the damage inflicted by the invading forces once they reached the planet. The pillaged cities quickly donned sinister appearances as all manner of vile monsters and mutants filled the streets with their ilk. Bodies swung from the light posts and the tanned hides of men adorned the sides of buildings.