The personal ship of Primarch Lion El'Jonson, the Invincible Reason led the Dark Angels effort in the Battle of Diamat and the Thramas Crusade. Following the Thramas ambush against the Night Lords, Konrad Curze became stranded on board the Invincible Reason for a time. However the Night Haunter found ample hiding places on the immense vessel, and terrorized the bowels of the ship despite repeated Dark Angels search parties. He eventually left the vessel when the Lion led the Dark Angels fleet to Macragge.
Upon the defeat of Curze on Macragge by the Lion, the Night Lords Primarch was again chained within the Invincible Reason. Following the abolition of Imperium Secundus and the journey by Roboute Guilliman, and Sanguinius through the Ruinstorm to try and reach Terra, the vessel was apart of the combined loyalist fleet. However upon the arrival at Davin, Sanguinius boarded the Invincible Reason and took the captive Curze with him for his own pilgrimage on the world, dispatching several Dark Angels guards through non-lethal force in the process. In the subsequent Second Battle of Davin the Invincible Reason engaged in a vicious duel with the Daemonship Veritas Ferrum.
- 1: The Lion (Novella) by Gav Thorpe, - The Primarchs (Anthology), pg. 225
- 2: The Unremembered Empire (Novel)
- 3: Ruinstorm (Novel)