The Ambassador-class USS Enterprise (registry number NCC-1701-C), built by the United Federation of Planets circa 2329-32. The ship was commissioned and launched in 2332 under the command of Captain Rachel Garrett, its only commanding officer. The Enterprise-C was lost at the Battle of Narendra III in 2344, having served for twelve years. It was destroyed in battle with four Romulan warbirds. Its destruction whilst defending a Klingon outpost paved the way for the Klingon-Federation Alliance.
Circa 2290, Starfleet began mass-production of the Excelsior class of starship. Considerably larger, faster and more powerful than the Constitution class (which was then phased out of service and retired), the Excelsior became the mainstay of Starfleet for almost a century, its spaceframe proving highly adaptable and easily upgraded to deal with new mission requirements and threats. The long lifespan of the Excelsior may have also been helped by the relative period of peace that descended following the Khitomer Accords of 2293: the Federation and the Klingon Empire entered into a more fruitful and cooperative relationship, which also seems to have discouraged aggression by other powers such as the Romulans, Tholians and Gorn.
By the late 2310s, however, the Federation saw the need to begin development of a new heavy starship design which could replace the Excelsior class. Increased contact with the Cardassian Union, previously a smaller power which had now launched a series of aggressive moves into the surrounding systems and in 2319 launched a devastating invasion of Bajor, may have been one reason for this decision. Gradually decreasing contact with the Romulans after 2314 and the fear that the Romulans were consolidating and rebuilding their forces may have also spurred a renewed period of Starfleet development.
That said, the Federation did not want to upset the balance of power in the Alpha Quadrant and was keen that this new ship's primary role would be peaceful, devoted to scientific research and diplomacy over combat. The new class was thus dubbed the Ambassador. The first ship of the class appears to have been launched in the late 2320s. Several more ships were laid down and under construction when word arrived in 2329 that the USS Enterprise (NCC-1701-B) had been lost in deep space after thirty-six years in service. The decision was made that one of the new ships would be dubbed Enterprise in honour of her service and the ships that came before her.
By the 2340s several dozen Ambassador class starships were in service and performing with distinction. Despite their formidable qualities, the ships appear to have not satisfied the need for a replacement for the Excelsior: there was rarely a situation which an Excelsior couldn't handle which an Ambassador could, and the continuing upgradeability of the Excelsior class simply made it more economical in terms of resources and construction time. It appears that by the mid-2340s the decision had been made to abandon the Ambassador class design in favour of an vastly more ambitious scheme: the Galaxy Project.
The USS Enterprise (NCC-1701-C) was launched in 2332 under the command of Captain Rachel Garrett. One of the youngest Starfleet captains commissioned since James T. Kirk, Garrett was noted for her toughness, excellent command judgement and canny command skills. Over the next dozen years the Enterprise-C dealt with dozens of tense diplomatic encounters, difficult science missions and several military engagements, from which the ship always emerged victorious. During this period the Romulans, who had become more reclusive, began a new period of aggressive skirmishing with both the Federation and Klingon Empire. The Klingons were also engaged in an eighteen-year period of conflict with the Cardassian Union which the Federation also refused to get involved with. An apparently tepid response by the Federation to these threats angered the Klingons, who, having recovered from the destruction of Praxis fifty years earlier, had begun having second thoughts about their new peaceful relationship with the Federation.
This brinkmanship resulted in the Battle of Narendra III in 2344. Four Romulan warbirds launched a direct assault on the Klingon colony at Narendra III, inflicting severe damage on the planet. The colony sent out a request for aid, which the Enterprise-C responded to. Although the ship was outgunned it nevertheless committed to the battle, inflicting severe damage on the Romulan vessels. Halfway through the engagement the damaged Enterprise-C suddenly underwent a spontaneous regeneration of its shields and weapon systems, suggesting that the Federation had developed some kind of new weapons technology, but the matter remains classified. Despite its valour, the Enterprise-C was destroyed with all hands. The ferocity of the attack had destroyed some of the Romulan ships and damaged the rest so badly they were forced to withdraw, saving the outpost from destruction (Star Trek: The Next Generation: Yesterday's Enterprise and Redemption, Part II).
Although the loss of the Enterprise-C was a serious blow to Starfleet, it had a remarkable effect. The Klingon Empire honoured the crew of the ship and convinced the Federation to renew diplomatic and military pressure on the Romulan Star Empire to cease its warmongering. This resulted in a brief tripartite peace agreement between the Federation, Romulans and Klingons. However, this lasted just two years before the Romulans broke the agreement and launched an attack on Khitomer in 2346. The ferocity of the attack stunned both the Federation and Klingons and almost resulted in war. This was only averted when the Federation instead found itself in a war with the Cardassian Union and the Klingons were distracted by internal politics. The Romulans, perhaps aware that they had nearly triggered a conflict they could not win, retreated entirely behind their borders for the next twenty years.
As usual, Starfleet moved to name a new starship Enterprise. However, aware of the Galaxy Project they decided not to name a new ship immediately and hold back until that project reached fruition.
The Enterprise-C was an Ambassador class starship, launched in 2332 and destroyed in 2344. It was an early-model Ambassador, featuring less advanced weapons and sensors than the models that entered service in the 2340s and 2350s like the USS Excalibur (probably the most famous ship of the class after the Enterprise), but still outclassing anything else in the Federation, Klingon or Romulan arsenals.
The Enterprise-C was 524 metres (1,720 feet) long, 283 metres wide (928.5 feet) and 102 metres (334.6 feet) tall. It had at least 700 crew, although some ships of the class by the late 24th Century may have had closer to a thousand. The ship had 33 decks and was the first class to use phase "strips" rather than the "banks" containing multiple phaser cannons used on previous designs. These strips allowed phaser fire to be directed from anywhere on their surface, massively expanding the angles of fire the ship could employ. This was tremendously useful when it came to handling multiple attackers simultaneously.
Andrew Probert's concept art for the Enterprise-C from ST:TNG's first season. He envisaged the ship as an evolutionary stage between the Excelsior and Ambassador classes.
Behind the Scenes
When Star Trek: The Next Generation entered production in 1987, the set of the meeting room was decorated with stylised versions of the previous ships to bear the name. It was assumed that the Enterprise-B would be an Excelsior-class starship, but the design of the Enterprise-C was unknown. Andrew Probert, who had designed the Enterprise-D and worked on the movies, created a sort of stumpy version of the Galaxy-class, which also drew on elements from the Excelsior as a kind of halfway house between the two. He also drew a colour sketch of what he imagined the ship looked like.
During the production of Season 3 two years later, it was decided to film a script called Yesterday's Enterprise. In this script the Enterprise-C is flung twenty-two years into the future and creates an alternate timeline in which the Federation is at war with the Klingons. The ship has to be sent back to restore the timeline. Rick Sternbach was tasked with designing the ship in a hurry and on a budget, so was able to just tweak Probert's design. Model-maker Greg Jein produced the final ship model for $10,000. This was a lot to spend on the model for a new ship, but it was helped by the fact that the studio had given the team a budget hike for the episode as it was going to air in a ratings "sweeps" week.
Yesterday's Enterprise was a massive, smash-hit success. It would go on to be named several times as the best-ever episode of the entire Star Trek franchise (although today it generally shares that honour with The Inner Light, The Best of Both Worlds, City on the Edge of Forever, In the Pale Moonlight and Far Beyond the Stars).
The Ambassador-class model was redetailed and altered to appear in subsequent episodes such as Redemption and the Deep Space Nine pilot, Emissary, but made no subsequent appearance. No CGI shooting model was ever built, leading fans to conclude that the Ambassador never fulfilled its original purpose of filling in between the Excelsior and Galaxy classes, with the Excelsior simply proving a much more successful and longer-lasting design than anyone had ever envisaged.