Games Workshop is preparing us for the Dark Angels with the backstory for the Dark Angel's confrontation with Luther and the destruction of their home world.
Dark Angel Lore "The Rock of Caliban" via WarCom
"Some Space Marines Chapters live in the most extravagant fortresses while others exist as fleet-based armies. Thanks to their home, the Rock, the Dark Angels have the best of both worlds. With the new codex supplement for the Dark Angels on its way, full of rules and exciting lore, we’re taking a look at the history of their mobile headquarters.
After fighting a galaxy-wide civil war you’d be hoping to come home to a nice hot drink rather than a barrage of laser fire. Unfortunately, that was just what Lion El’Jonson, the Primarch of the Dark Angels Legion, got when he returned to Caliban after the Horus Heresy.
Unbeknownst to the Lion, Luther – who had been like a brother to the Primarch in the days before the Great Crusade – had turned his back on the Imperium. Jonson attempted to contact Luther, but after only getting ‘message read’ responses to his hails, he was forced to return fire. Macro laser blasts and super-nuclear ordnance shook the very planet as the Primarch made landfall to confront his former best friend and mentor face-to-face.
No one ever truly discovered what happened in their battle, and even the Inner Circle (a closed network of the Dark Angel’s most senior warriors) only knows that a gibbering Luther was found, claiming that “the Watchers in the Dark had taken the Lion”. Fortunately, we all know that Luther is a totally reliable narrator…
Luther’s anguish echoed across the warp, causing a storm that, along with the Dark Angels’ bombardment, ripped the planet apart.* This tempest allowed the traitorous Dark Angels to escape throughout time and space, and those who remain loyal to the Lion have spent 10,000 years hunting down these so-called Fallen.**
What was left of Caliban is now known as the Rock. Larger than even the heaviest class of Imperial Warship, it is fitted with enormous engines, enabling the Chapter to travel the galaxy, seeking the Fallen, fighting the enemies of the Imperium, or just taking a nice leisurely Sunday fly around the Horsehead Nebula.
That’s about all we can tell you about the Rock before the Interrogator-Chaplain comes to torture us for giving away too many secrets.*** But fear not, the forthcoming Dark Angels codex supplement is absolutely packed with more information on this secretive Chapter, alongside extra details on their mysterious flying fortress-monastery and their ongoing hunt for the Fallen. "