The Invincible Reason was the first Gloriana-class vessel to be constructed. As a result, it had a level of detail and craftsmanship not seen in subsequent vessels. During the Great Crusade, Castellan Duriel was installed into its command chair and was in command of the vessel when The Lion was not aboard.
The personal ship of Primarch Lion El'Jonson, the Invincible Reason led the Dark Angels effort in the Rangdan Xenocides,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. Later during The Lion's Exterminatus of Barbarus the Invincible Reason was attacked by the Emperor's Children Heavy Cruiser Sybarite, which was now possessed entirely by a Daemon. The Invincible Reason was heavily damaged in the battle after the Sybarite rammed it. The vessel sought repairs on the Forge World of Thagria.
- 1: The Lion (Novella) - The Primarchs (Anthology), Chapter I
- 2: The Unremembered Empire (Novel)[Needs Citation]
- 3: Ruinstorm (Novel)[Needs Citation]
- 4: Scions of the Emperor (Anthology) - First Legion
- 5: Legacy of Russ, Part 8 - Fate Unbound
- 6: Dreadwing (Novella)
- 7: Lion El'Jonson: Lord of the First (Novel) Chapter 1 section II
- 8: The Horus Heresy: Legions