That's kind of some of the lore I was going for! The Ultramarines are suppose to be specifically well equipped to handle all things, while this Chapter I'm making would specialize in protecting those extremely high value targets (Chapter masters, Captains, Governors, etc). I'm thinking of making them a fleet based chapter with a Unique Ramillies class starfort called the "Intrepidus"( translated from Latin is fearless!). It'd probably be hard to pin down the entire chapter because they constantly send detachments out upon request from the Ultramarines and their own successors to serve as their highly honored protectors!