Battle of Tallarn

The Battle of Tallarn (010-011 M31) was a major conflict of the Horus Heresy, which saw the desolation of the Imperial world of Tallarn, and the birth of the famed Tallarn Desert Raiders regiments of the Imperial Guard. It was one of several planets that came under attack by the Iron Warriors after they had joined Horus in his rebellion against the Emperor.

After being abandoned by their Emperor's Children allies within the Eye of Terror, the Iron Warriors managed to leave, but the events of their escape dramatically altered the perceptions of their navigators. Once arriving at Tallarn, Perturabo was made aware of the Black Oculus hidden beneath the planet, and he immediately drew up plans to invade and secure the Cursus.

Initially, Perturabo destroyed all orbital and surface defense installations before virus bombing the surface, and he believed that he had obliterated the defenders. However, many tank regiments were hidden in shelters beneath the surface scattered across the planet, and they ventured into the poisonous world to attack those Iron Warriors who had landed. This led to a protracted battle that initially went in the Iron Warriors' favor until loyalist reinforcements arrived. Eventually, the Iron Warriors were able to capture, with the secret aid of the Alpha Legion agents, the shelter beneath the Sapphire City and use it as a secure staging ground upon the surface.

The Iron Warriors flooded the planet with troops and tanks, and their expected easy victory instead turned into a protracted war at a great cost to both sides of the conflict. Through the actions of the emissary of the Warmaster Argonis, the Alpha Legion agents, and Imperial Infocyte agent Iaeo, the Iron Warriors search for the Black Oculus was exposed, and they were forced to withdraw from the planet. Although the planet's surface was destroyed and many resources were lost in the defense, the battle was regarded as an important Imperial victory during the Horus Heresy.