|Location of Event :
||Near Archer IV 
|Stardate of Event :
|Nature of Event :
||Accidental creation of alternate timeline 
In the early 2340's, relations between the Federation and Klingon Empire were at a very low ebb. The Federation refused political backing to the Klingons foreign policy on several occasions due to Prime Directive concerns, something which the Klingon population regarded as a betrayal of the alliance. Public opinion in the Klingon Empire swung around to the view that the Federation was dishonourable and not to be trusted. Tensions escalated, until by 2344 many on both sides were openly talking of imminent warfare. During this year the Romulans attacked the Klingon outpost of Narendra III; the Enterprise-C detected the raid on her long range sensors and moved to assist despite facing a force of four Warbirds. The Enterprise-C managed to dispatch one of the Warbirds before being destroyed herself. The action of Captain Garrett in entering a hopeless battle and sacrificing herself and her ship over a point of principle was regarded by the Klingons as a profoundly honourable one, and led to a considerable easing of tensions. The Second Khitomer Accords were signed later in the year, leading to over twenty years of peaceful co-existence.
Recent temporal scans indicate that during the Narendra III battle, the detonation of several photon torpedoes opened a space-time rift through which the Enterprise-C passed. This created an alternate event sequence in which the Enterprise-C had been apparently destroyed before the Klingon outpost had realized that it was present and defending them from the Romulan attack. In this timeline, therefore, no record of the Enterprise C's involvement was made and the ship was marked as simply missing presumed lost.
Without the involvement of the Enterprise at Narendra III, a Klingon / Federation war began later in the year with an all out pre-emptive strike by the entire Klingon fleet. Starfleet fought delaying tactics, holding the Klingon advance up as much as possible, and this led to a prolonged war of attrition which lasted for some twenty two years and cost sixty billion lives.
Many elements of the preferred timeline remained in the alternate; the Enterprise-D was still constructed, but as a Battleship rather than an Explorer. This ship was devoid of families, and designed for heavy ship-to-ship combat and troop carrying. Much of the crew was different, although many of the senior officers remained the same. The most significant alteration was the Enterprise D's security officer, Lieutenant Natasha Yar; killed in 2364 in the preferred timeline, she was still alive in the alternate.
The Enterprise-D set about repairing the Enterprise-C for a return to Starfleet. However, an El-Aurian on board the D named Guinan proved to be sensitive to the changes in the timeline. Guinan explained to Captain Picard that the Enterprise-C must return to it's own time in order to restore the timeline; trusting in her intentions and sensitive to the possibility of an altered history, both Picard and Captain Garrett agreed to the plan.
Unfortunately, Captain Garrett was killed in a Klingon attack shortly afterwards. Command of the Enterprise-C passed to the ships First officer, Lieutenant Castillo, who was determined to carry on with the plan. After being told by Guinan of her fate in the preferred timeline, Lieutenant Yar requested and received permission to accompany the Enterprise-C as tactical officer.
The Klingons subsequently returned to the area and attacked both ships; the Enterprise-D remained in order to protect the C until it could travel through the rift. Although the D was destroyed in this battle, it succeeded in its mission and the C was returned to its own time.
However, this restoration was not an ideal one; the presence of Natasha Yar on board gave the Enterprise-C a much more experienced tactical officer, and this allowed the ship to both destroy two Warbirds rather than one, and to survive long enough without shields that the Romulans decided to attempt a boarding. Although Captain Castillo initiated a self-destruct sequence which was successfully completed, several dozen officers were captured - including the alternate Lieutenant Yar.
Yar subsequently agreed to become the consort of a Romulan officer in return for a guarantee that the other Enterprise-C officers would be allowed to live. She bore him a daughter, Sela, and lived on Romulus for five years. In 2349 Yar attempted to escape Romulus with her daughter, then four years old, but Sela raised the alarm and Yar was executed shortly afterwards. Sela later became an operative in the Romulan Tal'Shiar, and has been mostly concerned with attempts to disrupt the Federation / Klingon alliance.
Temporal Investigations ruled that the alterations to the original timeline, while significant, would be virtually impossible to correct since it would involve interfering with an battle which involved at least three separate nations. The current timeline is therefore judged to have become the preferred one.