The Invisible Ship (aka Stealth Blimp) is an experimental flying vehicle, owned by Ellicott-Chatham Technologies.
Its only appearance in the strip was when it "dropped off" Hannelore at the lake party at Emily's house. Hannelore was lowered onto the dock by a harness from what appeared to be mid-air; when questioned by Marten and Faye, she simply said, "Sorry, I'm not allowed to tell anyone."
Jeph attempted to make the ship "slightly visible" with an animated GIF that varied the background enough for the reader to see a silhouette of the ship. However, the outline was too "fuzzy" to make out any significant details of the ship.
Like other crafts in the Ellicott-Chatham Technologies livery, the craft has no human pilot, instead being flown by a sentient program. The AI is familiar with Hannelore, but does not get to be out of the test facility very much.
The vehicle apparently uses "stealth" methods to blend in with the background, such as miniature cameras and LED screens akin to those used in the James Bond movie, Die Another Day.
Names suggested for the vehicle, by members of the comic's discussion forums, have ranged from "Stealth Blimp" to "Invisible Airship" to "the Ellicot-Chatham Autonomous Dirigible Vehicle Imminent Presence."