Battle of Isstvan III
|Outcome||Pyrrhic Traitor victory|
|Traitor Space Marine Legions||Loyalist|
| Warmaster Horus Lupercal
First Captain Ezekyle Abaddon
Captain Horus Aximand
First Captain Calas Typhon
Lord Commander Eidolon
Master of Ordnance Durak Rask(d)
Princeps Esau Turnet
| Captain Garviel Loken|
Captain Tarik Torgaddon (d)
Captain Saul Tarvitz (d)
Captain Ehrlen (d)
Captain Ullis Temeter (d)
Captain Lucius (defected)
Lieutenant Crysos Morturg
Magos Calleb Decima(d)
| Sons of Horus
World Eaters traitors
Death Guard traitors
Emperor's Children traitors
|High||All forces save two|
An Imperial Expedition had assembled at the Isstvan system consisting of elements of the Sons of Horus, World Eaters, Death Guard and a contingent of the Emperor's Children. Overall, over 200,000 Astartes were assembled for the operation.
The Death Guard Legion received a distress signal from the former Imperium world of Isstvan III which stated that the colony had turned away from the Imperial Truth and that the former governor Vardus Praal was leading the rebellion. The assembled Imperial expedition was tasked with eliminating this threat. Initial skirmishes were fought on the outer system world of Isstvan Extremis where the Emperor's Children and Death Guard had managed to eliminate the enemy outpost.
With the enemy forces blinded, Warmaster Horus brought about the Legions to hammer the rebel forces.
War against the Isstvanians
A combined assault was assembled by the Legions which invaded the planet determined to remove the threat of the rebels. Due to incorrectly mapped locations, many of the drop pods that crashed at Choral City slammed into the city's towers which caused a delay in reinforcements as they were pinned in inaccessible locations. The Titan Dies Irae was also present at the planet and made use of its mighty weapons to eliminate heavy enemy positions.
Hundreds of Isstvanian soldiers had assembled to fight against the threat of the Imperials. Though they lacked the genetically engineered nature of the Space Marines, they defiantly fought against them with some succumbing to the unique weapon of the Isstvanians. A more dangerous threat to the invading Astartes were the Warsingers among the rebels which managed to kill dozens of Space Marines.
Vardus Praal himself was killed by the Emperor's Children Astartes Lucius.
With those squads and their leaders that were known to be completely loyal to the Emperor on the planet, the Warmaster finally decided to initiate his plan. A number of starships had secretly prepared the Life Eater virus for deployment onto the planet. A signal was sent by Horus who informed his loyal troops such as the Princeps of the Dies Irae of the attack allowing them to seal all doors to prevent the virus from infecting the crew. After which, the ships began to fire onto the planet itself. The assembled Remembrancer Order was present on the Vengeful Spirit while this happened. After Horus declared his intentions of taking the Golden Throne, his Astartes went about exterminating the Remembrancers. The virus itself devoured and destroyed hundreds of Astartes on the planet as their armour afforded them no protection from the deadly bio-weapon with even the rebelling Isstvanians dying in the genocidal attack. All that was left was a sludge of dead organic matter after which a single blast was directed at the planet which created a firestorm which scorched the world leaving it a dark dead planet.
Despite his carefully laid plan, the loyal Astartes were not eliminated and many were warned of the betrayal by the Emperor's Children Saul Tarvitz. This consisted of elements of the World Eaters, Sons of Horus, Death Guard and Emperor's Children who managed to find bunkers or other sealed locations to survive the firestorm. Once this was over, they began to take stock of their position. Horus himself was outraged, not only at this but that Angron the Primarch of the World Eaters landed on Isstvan III without permission and attempted to fight against the remaining loyalists. This forced the Warmaster's hand to fight against the surviving Astartes on the planet in order not to show weakness to his brothers and that he was committed to the goal.
Seeing that they were betrayed, Captains Garviel Loken and Tarik Torgaddon of the Sons declared to the surviving Astartes of the XVI Legion that they were once again the Luna Wolves and marched to Praal's stronghold, where they dug in with the surviving members of the Emperor's Children under Saul Tarvitz and combated against the traitor forces. While bringing about grievous casualties to Horus's forces, the defenders were dwindling rapidly due to their limited numbers. They had hoped to bring about a high number of casualties for the Warmaster and to delay him, thus giving the Emperor's loyal forces time to reach the Isstvan system. They managed to repel wave after wave led by various commanders such as Lord Commander Eidolon who was forced to scurry away after the loss of his Chaplain Charmosion.
It was believed that they would have been capable of holding out the Traitor forces for some time. However, Lucius had grown to despise Saul Tarvitz and wanted to rejoin his Legion. Using the slain Chaplain's helmet communicator, he contacted Lord Commander Eidolon and arranged for the betrayal of his comrades. Lucius himself had slain all the defenders at that part of the encampment promising Eidolon not only glory by defeating the loyalists but giving him the head of Saul Tarvitz. Despite his boast, Lucius was defeated when Tarvitz had reinforcements forcing Lucius to flee back to the Emperor's Children Legion.
While this was occurring, Garviel Loken and Tarik Torgaddon snuck away in order to confront their former fellow traitor members of the Mournival; Ezekyle Abaddon and Horus Aximand. Despite a valiant battle, Torgaddon was slain and Loken was buried under rubble from a Titan's blast.
The defenders were now too few and Horus's patience had dropped to the point that he ordered the Dies Irae to destroy the loyalist fortifications. Many more were killed in this action leaving a small band of survivors. With great reluctance, Angron was recalled by the Warmaster as were the other Traitor forces who returned to their ships. This time, Horus planned to finish off his enemies once and for all. He commanded the great ships in orbit to begin bombarding the planet which killed any remaining defenders which included the fatally wounded Garviel Loken.