The USS Enterprise NCC-1701 disappears

Dr. McCoy jumped through the Guardian of Forever. The USS Enterprise NCC-1701 began to disappear. First, the nacelles disappeared. Then, the secondary hull disappeared. Finally, the saucer section disappeared. The Guardian of Forever told the landing party "Your vessel, your beginning, all that you knew, is gone." The landing party realized that the past had been altered and the Enterprise - along with the entire Federation - no longer existed.