Night Watch
The Night Watch (no relation to the book or movie of the same name, though perhaps some inspiration taken from the Night's Watch from A Song of Ice and Fire) is a loyalist Space Marine chapter part of the Astartes Praeses, a group of twenty space marine chapters whos duty it is to guard the regions surrounding the Eye of Terror. They are based on the planet Silence (Night Watch, Silence, I see what theme they are doing here...) which is directly north (How can something be "North of something" in space?) of the Eye of Terror. They are noted to not be strict adherents to the Codex Astartes, as during the 13th Black Crusade they fielded eleven companies of Space Marines. It could be, being so near the Eye of Terror that the Night Watch feel the need to maintain more companies then normal to keep their battle strength up, in the face of constant warfare from the Traitor Legions.
They have taken part in two major actions, the 13th Black Crusade where they devoted eleven companies to the action, and the Zeist Campaign against the Tau Empire where several Night Watch Tactical Squads took part.