Battle of Deep Orbital DS191
The Battle of Deep Orbital DS191 was a campaign of the Great Crusade. The campaign was waged shortly before the Horus Heresy when much of the Emperor's Children, Fulgrim included, were already on the road to corruption.
The campaign saw the Emperor's Children and Iron Hands work together to clear Ork forces on the space station Deep Orbital DS-191 in the Callinedes System. In truth, it was used as an opportunity to try and bring Ferrus Manus into Horus' fold. As the rift between those closer to Fulgrim and those who would ultimately remain loyal to the Emperor was festering within the Legion, commanders such as Solomon Demeter were unsupported by those closer to the Primarch such as Eidolon, Marius Vairosean, and Julius Kaesoron. While ultimately the Emperor's Children prevailed, Commander Vespasian saw their actions as dishonorable, and when he protested to Fulgrim he was murdered by the corrupted Primarch.