Deep Black is a highly secret NSA department.
The term is really a covername for the department whose real name is Desk Three, or NSA's Combined Service Direct Operations Division. This newly formed section was created under the premise that modern technology had progressed so far that it had remodeled the Intelligence world and no existing agency was fully equipped to take advantage of it. All the existing agencies fought for the right to put this group together, CIA, DIA, Defense Department, State Department, and others but the NSA won the battle.
In addition to access to all the technology, Deep Black had a small cadre of highly trained operatives who were able to head into the field when needed. These operatives do not enter the field with just a cloak and a dagger, however, but with the ultimate in modern surveillance equipment. Making constant use of a plethora of satellites able to monitor incredibly small events on the planet, much of the intel that the operatives need can be provided by people sitting in a room in Maryland.
Much, but not all. Satellites still have trouble with heavy cloud cover. They cannot see inside buildings, infrared detection notwithstanding, and they cannot interrogate people from a distance. For that, feet on the ground are vital. Deep Black does not employ a large number of operative but those they do have are quite good.
One of the first and best of these agents at the beginning of the series is Lia DeFrancesca. Caustic as she is beautiful, she loves the technology that she is given but isn't afraid to shut it off and take over herself when it calls for it. She can shimmy up a drainpipe, disarm a guard, plant a bug, and kick butt with the best of them and look great doing so. Don't tell her that, however, unless you are ready for one of her deflating glares.
The other star of the series is Charlie Dean, a decorated ex-Marine sniper, a veteran of Vietnam and other conflicts. Now retired, he is asked to provide an impartial viewpoint on the first recorded assignment and remains throughout the series. Dean doesn't like the technology as he feels it is far too unreliable. A product of his generation, Dean is far from a Luddite but has had equipment fail at the worst time too often to put any trust in it. Use it if it is there but don't depend on it is Dean's attitude.
The third agent of note is the young (23) agent Tommy Karr. Though he has not a lot of years under his belt, Karr has a maturity that is belied by his joking, frolicking manner. Despite his smiles and teasing, Karr is seasoned, smart, dangerous, and dependable.
These three make up the field side of things in the series. Back at headquarters are another set of characters headed by the stern spymaster Reubens who decides who goes where and sometimes who doesn't come back.