Tantive IV is the diplomatic craft used by Princess Leia to transport the stolen Death Star plans. The Tantive IV is captured by a Star Destroyer which is under the control of Darth Vader. When the Tantive IV is about to be captured, the plans for the Death Star are hidden on the droid R2-D2 who escapes to the planet of Tatooine below with C-3PO.
The craft is seen at the end of Star Wars III - Revenge of the Sith where Obi-wan Kenobi, Yoda and Bail Organa are seen discussing the next course of action. The first scene of a New Hope and last scene of Revenge of the Sith both take place on board the Tantive IV and the aptly the first and last words respectively are said by C-3PO.