The Battle of Tallarn
Credit: Cover of Tallarn: Executioner
In a devastating surprise attack at the time of the Horus Heresy (circa 010-012.M31), the Iron Warriors Chaos Space Marines struck the fertile Agri-World of Tallarn. Thousands of virus-bombs rained down on Tallarn and the people ran to their enviro-shelters, deep beneath the surface. As they hid, safe from the devastating bio-infestation, the deadly coils of DNA mutated as they were programmed to do. Animals, plants, even insects died as the virus did its work, destroying the planet's ecosystem and leaving an empty shell devoid of life.
After seven weeks of isolation, the survivors of Tallarn emerged upon the surface. They found a world covered with the acrid slime of plants and corpses not yet decayed - for the world was completely sterile, without even bacteria to aid the decomposition of its dead. The surface was deadly to organic life forms, humans and even Space Marines dying within minutes of exposure and the only way to move around in the surface was in air tight vehicles with crew in environmental suits as a safe guard.
The Iron Warriors sent a small ground force to wipe out the survivors on the surface believing resistance to be minimum. The survivors whom survived by hiding in their underground bunkers, emerged to do combat this force using guriella hit and run techniques. Soon, reinforcements from both sides arrived, rival space fleets bringing vast armies to fight over the worthless remnants of this dead planet. The Battle of Tallarn raged for many months and was the largest armoured conflict of the Horus Heresy. Outbreaks of viral infection from rogue viral DNA residue made it almost impossible for infantry to operate outside their protective shelters or the environmentally sealed compartments of their tanks. The battle was finally decided by the vast armies of tanks deployed by the Traitor and Loyalist forces. When the fighting ended, the empty, putrid desert wastes of Tallarn were littered with the wreckage of more than a million shattered vehicles and the Imperium stood victorious over a dead planet.