Originally Posted by Cheesegear
Guilliman subsequently ordered the Imperial Fleet to bombard Dorn's fleet with torpedoes until he gave in.
/slowclap for Guilliman. In order to prevent civil war, Guilliman was willing to start one. Using non-Astartes military. In a massive clusterf* of "What is this I don't even..." because Dorn was the one who was supposed to be giving orders with the Emperor (and Horus) down, and Malcador being a pile of ash.
And then one of the chapters the Fists got split into told Guilliman to go boil his head, and the Black Templars never looked back.
At least, that's roughly what I think happened. The more lore savvy people will probably chide me for being horribly, horribly wrong about every word of that sentence.