Battle of Anuari
Following the dissolution of Imperium Secundus, the combined fleets of the Ultramarines, Dark Angels, and Blood Angels led by their respective Primarchs Roboute Guilliman, Lion El'Jonson, and Sanguinius attempted to return to Terra and the Emperor. However the Ruinstorm made Warp travel highly difficult if not impossible, and the fleets struggled to make even short jumps. The traitor fleets, powered by Chaos, had less difficulty and were able to ambush the Ultramarines fleet near the Anuari System.
Guilliman would find himself temporarily cut off from the rest of his fleet with only the Strike Cruiser Cavascor attending his flagship. From the Battle Barge Samothrace, Guilliman found the two Ultramarine ships attacked on three sides by a Word Bearers, World Eaters, and Night Lords force led by the Battle Barge De Profundis. Guilliman pulled his fleet into a defensive formation and had his Destroyer Squads board enemy ships. The Word Bearers commander Toc Derenoth had foreseen this and ran his vessel into the firing arc of the Samothrace and Cavascor. The shards of the De Profundis slammed into the Samothrace. Although several of the shards were destroyed due to point defense fire and the void shields of the Ultramarines vessel, some managed to break into the hull, disgorging hordes of Word Bearer Astartes. During the struggle aboard the Samothrace, Guilliman personally led the counterattack and managed to slay Toc Derenoth in combat and push the Word Bearers back. However Guilliman fell into another ambush, and now faced the two Dark Apostles Phael Rabor and Quor Vondor, each armed with an Athame blade. Guilliman defeated them, but the two traitors laughed that they had already won. After the deaths of the two Dark Apostles, the rest of the Ultramarines fleet reached the site of the battle, managing to surround and completely destroy the World Eaters and Night Lords fleets as well as the remaining Word Bearer vessels.
After the battle, several captured Chaos Navigators allowed Guilliman to more easily navigate the Ruinstorm. Moreover he had become partly tempted by the power of the Athame blades and instead of destroying them locked them in his vaults in hopes of studying them and possibly using them against the traitors.