Macrinus was a Captain in the Ultramarines Chapter when the Ork forces of The Beast invaded the Imperium.[1a]
He commanded the Strike Cruiser Chalcedon, when the Ultramarines' fleet fought against one of The Beast's Attack Moons that had appeared above the Imperial world of Tarentus. However, he was later ordered to leave for Terra by his Chapter Master, Odaenathus, after the Ultramarines received word from Terra that their aid was requested for a strikeforce to attack the world Ullanor, which was discovered to be the origin point of The Beast's invasion force.[1a]
He later appeared before Lord Commander Koorland as part of his Chapter's taskforce on Terra.[1b]