The standard Klingon warship during the era of the original five-year mission.
The D7 class was the main Klingon warship seen in the original series, a vessel with a bulbous forward command pod on a long neck and a flattened rear hull with two engine nacelles. It was the ship that defined the look of the Klingon fleet in the 2260s.
D7 cruisers appear in several third-season episodes, including Elaan of Troyius and Day of the Dove, and in The Enterprise Incident a fleet of Romulan ships of the same design is shown, suggesting that the two powers had shared technology. Klingon commanders such as Kang captained these ships in their encounters with Captain Kirk.
The design was updated for the films as the K't'inga class, which appears in the opening of Star Trek: The Motion Picture when three Klingon cruisers are destroyed by V'Ger. The D7 later reappears in Deep Space Nine's Trials and Tribble-ations, which revisits the original series era.