Atonement - History: Mankind first settled Atonement when Human colonists arrived in sleeper ships before the Great Crusade. Those settlers died, probably of heavy metal poisoning, before their colony was even completed. The ruins of their vessels remain on the planet as a monument to early Human interstellar history.Human settlers established a new colony on Atonement in the waning days of the Imperial Jericho Sector. Equipped with a broad range of filtration devices, these settlers chose the name "Atonement" to honour the ancients who had desperately attempted to tame this world.When Imperial contact and support were lost during the onset of the sector's "Age of Shadows", troubles swept through the colony. As filtration equipment failed, construction stalled. Like the first attempt, many of these settlers died of heavy metal poisoning. Unlike the ancient settlers, some members of this colony survived in isolation.The few million who dwell on the planet today are descendants of the surviving settlers. They are a stubborn and sickly lot, dependent upon the few remaining filtration systems that have been maintained through the millennia.Many have genetic modifications that enable them to better tolerate the planet's living conditions, though even with these their life expectancies are far shorter than Imperial averages. Aside from filtration, their technology base is far below that of the modern Imperium, almost entirely dependent upon petrochemicals for their energy base.The natives initially rejected Imperial interference when the Achilus Crusade made contact. A show of force, which included an example of orbital bombardment, quickly convinced them to change their minds.They have shown lip service to the Imperial Cult, and have begun to provide limited mining resources to the crusade. The ever-present taint of heavy metals prevents most Imperial units from utilising agricultural products provided by Atonement.In early 815.M41, a Tyranid Hive Ship with its entourage was seen entering the system. A few vessels that were in orbit attempted to engage the fleet, while a pair of destroyers were dispatched to send a plea for reinforcements. One of those destroyers, Thorn of Truth, made contact with elements of the salient stationed at Castobel.A sizeable fleet element was dispatched to Atonement, with orders to make every effort to hold the planet. When they arrived, they found only Tyranid vessels in system, and a world already seeded with Tyranid spores. To their surprise, however, the planet's natives responded to vox inquiries and explained that they were maintaining a defensive action against overwhelming numbers of xenos.Support units rapidly deployed to the planet, as the fleet launched a counter-assault against the Tyranid vessels. The battles still rage both on land and in the void. Though the odds are not in their favour, the Imperial defensive efforts -- especially on the surface -- seem to be going better than expected.The organisms involved in the attack appear less vigorous in their actions than those observed throughout the salient. Agents of the Adeptus Mechanicus have not determined if this is due to the planet's contaminants or another unidentified variable.