The Black Chamber is United States Cryptanalysis agency officially disbanded 1929, secretly retasked with occult intelligence duties. The Black Chamber is the US equivalent of The Laundry. However, the Black Chamber is portrayed as much more sinister and secretive than the Laundry, as the nature of their operations are rarely known in detail. The name "Black Chamber" itself is the designation the Laundry had given to the organization: its internal name is Operational Phenomenology Agency (OPA). They are also called the Nazgûl in reference to the black riders from Tolkien.
First Appearance: The Atrocity Archives