The sixth ship and the first Starship to carry the name Yorktown was NX-05, an NX class (some refer to the class as Enterprise class) ship. This ship was one of the first Earth Vessels to explore deep space in the 2150s-80s, even after the more modern and advanced Daedalus class was commissioned in the 2160s. This ship was responsible for exploring several star systems that would soon be colonized by settlers from Earth and Federation members. She was decommissioned in 2191 and sat, mothballed, in Earth's orbit near the San Francisco Fleet Yard for nearly ten years before being restored and becoming one of the first ships in the Starfleet Academy.
The second Starfleet ship and First Federation Vessel  to bear the name Yorktown was also the seventh ship to carry on the name. She was a Constitution class Starship built in 2250. This ship servered the Federation proud while she explored the 'Final Fronter' from the 2250s to 2280s. In 2284 the ship was refit. In 2286, after an encounter with a probe sent to Earth to find out why whales were no longer present, the ship was towed to space dock to under go repairs from it's encounter with the probe. While there, the ship was renamed Enterprise-A and placed under the command of Captain James T. Kirk. After being renamed, this ship continued on to earn high praise for her new crew, after a few minor bugs were fixed. In 2287 the ship was hijacked by the Vulcan Sybok who was looking for the mythical 'Sha Ka Ree'. In 2293, the ship was sent to escort the Klingon Chancellor Gorkon to Earth for peace talks following   an explosion on Praxis, but due to a conspiracy between Klingon and Federation members and an attack by a cloaked Bird of Prey, this falls apart. However, after resucing Captain Kirk and Dr. McCoy from the Klingon mining prision Rura Penthe, the ship and crew, with help from Captain Sulu and the USS Excelsior, were able defend the peace talks from the Bird of Prey that was able to fire while cloaked. This opened a new era between the Federation and Klingons.
				The next USS Yorktown was commissioned in 2296 was an Excelsior Class ship. The NCC-1717-A made a name for herself in 2301 when she alone protected a Federation colony from an attack by the Tholians who claimed the planet was in their territory. Alone, the Yorktown stood her ground against five Tholian ships, re-earning the Yorktown's nick name from Earth's CV-10 in World War Two, 'The Fighting Lady'. NCC-1717-A destroyed three of the attacking ships, damaged another, and succeed in keeping the Tholians from firing on the colony or landing troops. In 2323 the ship was again in battle, but this time against the Romulans. In a border clash akin to the incident in 2266 between the USS Enterprise and a Romulan Bird of Prey, the Yorktown responded to a report of an attack on a neutral zone outpost. The Romulans wanted to test their newest cloaking technology as well as upgraded plasma torpedoes. The Yorktown was able to repel the attacking ship, but took massive damaged, loosing more then half her crew. The ship was towed to a Starbase by the USS Lexington, but Starfleet decided she was too badly damaged to be repaired and they decommissioned the ship. NCC-1717-A was scrapped two weeks later.
						Two years later, in 2325, the next USS Yorktown, NCC-1717-B, was commissioned at Utopia Plaitia Fleet Yards. One of the new Constellation class ships, this Yorktown would have a short life. In 2340, the ship was returning from a trip to the Klingon Homeworld of Qo'noS, when she encountered a sever ion storm near the border. The ship suffered a total power loss which allowed matter and anti-matter in the warp core to come in contact and cause a core breach that destroyed the ship. At first, Starfleet assumed the Klingons attacked the ship, but after a joint investigation the truth was learned. This allowed the two powers to work together toward a common goal and aided Federation and Klingon relations, improving them greatly. It also meant that future encounters between the two powers, the Enterprise-C's defense of the Klingon Outpost on Narendra III in 2344 and Starfleet's aiding of the Klingons after the 2346 Khitomer massacre would bring the two closer and eventually become allies.
The fifth & Current  Starship to carry on the name Yorktown was commissioned in 2347 as an Ambassador class vessel. Currently the Yorktown  is taking part in the first Federation and Klingon joint operation. The Yorktown and a K'tinga Class Battlecruiser is conducting a joint investigation of Setlik III. Many hope it ushers in a new era of cooperation between the two powers. Captain James D. Sowards is the current  Yorktown Commanding Officer.