a chapter of righteus space nazis.
The Ultramarines kind of do everything well, and they're the most tactically flexible chapter of Space Marines, able to move freely around the board shooting while picking and choosing the combats they want to be involved with.
The Ultramarines are considered one of the strongest and most honoured of all the Space Marine Chapters in the Imperium of Man, and were responsible for almost single-handedly holding the Imperium together after the Horus Heresy.