The Black Squad are a special unit of Wulfenbach troops which have an as-yet-unexplained ability to apparently appear and disappear from thin air (a sort of European ninja, if you would). For as-yet unspecified reasons, Ardsley Wooster quailed at seeing them appear to accost Zeetha and himself. This could refer to anything from the level of their skills to their being shades of the dead.
However, that latter possibility appears to have been quite definitely eliminated, since Sergeant Scorp, returning to duty with Wulfenbach ground forces in Mechanicsburg after having been treated for an injury to his arm in Mechanicsburg Hospital. However, we saw Sergeant Scorp with the Black Squad, he was not wearing their special uniform; thus, he was apparently not part of the Black Squad itself. Even so, and despite the fact that a member of the Wulfenbach forces is likely to see many strange things in his career, simply the fact of his easy familiarity with the members of the Black Squad seems to militate against the notion of them being ghosts.
Their black uniforms and disappearing act could also be technical tricks of the Baron intended to create the impression of them being ghosts; in that case, though, we would not expect Wooster to be fooled, as his ability and knowledge have been demonstrated on numerous occasions. This doesn't, however, eliminate the possibility that in Wooster's previous career, of which we have little knowlege, he might have had experiences with the supernatural of such a nature that even something that merely suggests the supernatural would make him uneasy.
The black squad is co-ed, unusually for ground forces. All other Wulfenbach ground forces shown so far are all men, with one (possible) exception.. One of the members, possibly an officer, is a woman. She appears earlier in Vol 6 - recognizably the same person as appears apprehending the supposed Heterodyne, where in the next page Sergeant Scorp calls her "Ma'am", suggesting a superior officer.
Zola "Heterodyne" (or, more precisely, Herr Vikel) had a device which seemed to warp the squadmembers painfully out of existence. Because the Black Squad has previously been shown appearing from, and disappearing into, nowhere as part of their normal operations, it is unknown if this is a permanent dematerialization, or simply a temporary banishment to their usual hiding place.
Their variation of the Wulfenbach badge is the tower and wings in matte black on a gold oval, and is worn on their shakos.
- Night Master - Assassins with a similar disappearing/reappearing power