Captain Halbrecht was aboard the Phalanx when the starship Eisenstein was intercepted. While the Captain was not present alongside his Primarch Rogal Dorn when Death Guard Captain Nathaniel Garro, Luna Wolves Captain Iacton Qruze, Remembrancers Mersadie Oliton and Euphrati Keeler gave their account of Horus' betrayal at Isstvan III,[1a] he did play an important role in subsequent events that determined their fate. In particular, Halbrecht and the Astartes under his command were responsible for guarding Keeler, Qruze and Garro until their custody was transferred to the Silent Sisterhood on Luna.[1b]
Along with his fellow Captain Efried, Halbrecht took a conservative and cautious approach to the survivors of the Eisenstein, considering the possibility that instead of being loyal to the Emperor and having escaped from their respective Legions, they might themselves have turned against the Emperor (since their claim that Horus and several of his fellow primarchs had turned traitor was almost impossible to believe). Later, upon conversing with Garro, he clarified the reasoning behind his reservations and those of his primarch, citing the need for precaution and hoped his behavior and that of other members of the Imperial Fists were not taken personally.[1b]
However, Iacton Qruze and Nathaniel Garro had spoken the truth and the Horus Heresy soon engulfed the Imperium. Several years later into the Heresy, when the Alpha Legion began their attack on the Sol System, Halbrecht had been promoted to the rank of Lord Castellan and given the title Fleet Master within his Legion; as well as being given command of Terra's Second Sphere of defense at Uranus, by his Primarch. During the final phase of the Solar War shortly before the Siege of Terra, Halbrecht oversaw the defenses of Uranus from a massive attack led by Perturabo himself. Though successful in stalling the traitors for several days and retreating to Jupiter with the majority of his fleet in order to make another stand with Captain Efried, he was eventually forced to withdraw to Terra aboard his Battle Barge Monarch of Fire.
- 1: The Flight of the Eisenstein (Novel) by James Swallow
- 2: Praetorian of Dorn (Novel), Part 1 - Chapter 4
- 3: The Solar War (Novel) - Chapter 15