Goa'uld escape ship
Space-fairing vessel developed for the single purpose of allowing a colony of cloned Goa'uld (all stemming from on born of Cronus' queen, later implanted within Adrian Conrad) to escape Earth and return to the stars.
The symbiotes took over the residents of the small town of Steveston, Oregon, where they constructed the ship at night in secret. The ship's existence was the only reason that the N.I.D. allowed the Goa'uld to continue operating, observing them with the plans to take the Goa'uld ship when it was complete.
SG-1's arrival in the town interrupted the N.I.D.'s plans, forcing them to move long before the ship was finished. The symbiotes were killed leaving the townspeople none the wiser, and the unfinished ship was likely taken to Area 51 for study. It is possible that this ship furthered the U.S. military's endeavor to create the first X-303 vessel, Prometheus, which was completed a few months later.
Nightwalkers - Carter, Teal'c, and Jonas uncover blueprints for the development of a Goa'uld craft, and find the ship itself under construction in a dry-dock.