The Stealth Conjoiner Drive, as called a quiet drive, improved drive topology and reduced tau-neutrino emissions by two orders of magnitude -- not perfectly undetectable, but far more so than its predecessor. It was designed, tested, and built by the Mother Nest to allow interstellar travel to resume without fear of drawing the Inhibitors to human-occupied space. Nightshade was the first vessel equipped with the stealth drive.
While gloating about its abilities to Nevil Clavain, one of the architects of the project, Skade, announced that only Conjoiners would be allowed to possess the improved drive. However, this later proved irrelevant, as Aura provided Clavain's faction with the schematics for dark drives. While vastly superior to the Conjoiner-designed counterparts, dark drives also had a secondary advantage: they could be installed on existing Conjoiner Drives without a risk of a fatal overload.