Battle of the Caliban System
The stage for the battle was set when Cypher turned himself in to the Inner Circle of the Dark Angels. He revealed the intent of the Fallen Angel Astelan and Typhus of the Death Guard to use the Tuchulcha and its brother engines to create a time rift in the Caliban System and transport the Fallen from ten thousand years previous to the 41st Millennium. The Fallen would then combine with Typhus' own forces in combination with recently captured Gene-seed, creating a new Legion known as the "Death Angels". Horrified by this notion and after convincing by the Watchers in the Dark, Dark Angels Supreme Grand Master Azrael agreed to work with Cypher to foil the traitors plans.
The entirety of the Dark Angels led by The Rock eventually arrived at the Caliban System just as the Plague Fleet of Typhus supported by other traitor ships did. A massive space battle broke out between the two fleets, as traitor forces boarded The Rock itself. Led by the Terminus Est, the Chaos fleet was large but disorientated, with Typhus himself more concerned with his warp ritual. The traitors were able to open the Warp Breach first, and it seemed that their plan to rewrite history and doom the future would succeed. However Azrael was eventually able to order Tuchulcha to scatter all those near the time portal, inadvertently including the Fallen ten thousand years earlier as well. Meanwhile, an Unforgiven fleet from the Angels of Absolution, Repentant Brotherhood, Angels of Redemption, and Angels of Vigilance arrived to the rear of the remnants of the Chaos armada, scattering it.[1a] The Warp Breach created by the Chaos forces was finally closed by Ravenwing Black Knight Annael at the cost of his own life.[1a] While the Dark Angels were victorious, a third of the Chapter was wounded or slain in the battle.