The Black Vipers are a Loyalist Space Marine chapter created from the Salamanders Geneseed. Formed during the Ultima Founding, the Black Vipers are comprised entirely of Primaris Marines. Their secretive and isolationist nature meant very few Imperial units ever fought beside them. This behavior extended to the Salamanders who only discovered their existence by accident years after their Founding.
Two things of note are the agents of Archmagos Dominus Cawl that appear to be monitoring them and the disappearance of a Salamander Chaplain while travelling to them. Due to this disappearance, the Black Vipers are currently ignorant of the Promethean Cult. It is speculated that the Black Vipers may be serving as Cawl's own personal chapter of space marines, although the evidence of this is slim at best;the only things that suggest this are the red and black color scheme and the mention of the fact that "Whenever the Chapter has been identified, agents of Belisarius Cawl have never been far away."
On the Tabletop
Colors and Heraldry
As seen in the picture, black with dark red backpack, knee guards and insignia.
The head of a striking red viper centered on a black field with dark red borders.