Sacrifice of the Enterprise-C at Narendra III

In 2344 Romulan warbirds attacked the Klingon outpost on Narendra III. The USS Enterprise NCC-1701-C, under Captain Rachel Garrett, answered the outpost's distress call and placed itself between the attackers and the defenseless colony, even though the Klingons were not yet the Federation's allies.

During the battle a burst of weapons fire opened a temporal rift that carried the battered ship twenty-two years into the future. Its disappearance changed history: in that altered 2366, the Federation was losing a long war against the Klingons, and the Enterprise-D was a warship. Guinan sensed that something was wrong, and Captain Picard accepted that the Enterprise-C had to go back. Lieutenant Tasha Yar, who in the original timeline had died in 2364, volunteered to join its crew.

The Enterprise-C returned to Narendra III and was destroyed defending the outpost, restoring the original history. The sacrifice deeply impressed the Klingons and is credited with helping to cement the Federation-Klingon alliance. Yar, captured by the Romulans, later bore a daughter, Sela, who would play a role in the Klingon Civil War.