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Notes : Perhaps the most famous class of vessel in Starfleet history, the Constitution class was a legend in its own time. When launched, the USS Constitution set a new standard of excellence in almost every applicable field - she was simultaneously the fastest ship, most advanced exploration platform and most powerful combat vessel in known space. The four hundred and thirty crew enjoyed a standard of crew accommodation unknown on other vessels of the period, while the diplomatic facilities rivalled those of all but the most elaborate Starbases.

Quickly following the Constellation in 2245 was the USS Enterprise, NCC-1701. This was to become the most famous vessel in Federation history; during her forty years of service life the Enterprise explored countless new worlds, making first contact with many species and expanding the Federations knowledge of the territories surrounding it hugely. Like her sisters the Enterprise also served as a mighty deterrent to both the Klingons and Romulans, several times taking part in combat actions which determined the fate of the entire Federation if not the Alpha Quadrant itself.

The Constitution class ships where designed for long duration missions with minimal outside support, and exploratory missions typically lasted up to five years. The Enterprise conducted several such missions, first under Captain April and then under Captain Pike followed by Captain Kirk. Kirk captained the Enterprise through her most difficult missions, and it is largely because of his incredible success that the Constitution class has acquired the reputation it has.

By 2265 the early Constitutions where reaching twenty years of age, their designed life span. Starfleet had decided that they where becoming somewhat long in the tooth and was looking for a replacement class; however, such was the popularity of these ships that the Starfleet design bureau stated in an official memo that none of the contemplated new designs matched up to them and the best course of action was to simply rebuild the existing ships with the latest technology. Although Starfleet was not convinced at first, careful testing of the skeleton framework of several Constitution class ships revealed that the basic structure was more than capable of continuing in service, having withstood twenty years of hard use with ease.

The USS Enterprise was selected to be the first ship to undergo such a refit, and in 2269 she went into spacedock in Earth orbit for eighteen months of work. Never in Starfleet history has any vessel been so comprehensively updated - essentially a new vessel was built onto the bones of the old, replacing virtually every major system. The Enterprise was rushed out of Spacedock in 2271 to face the threat presented by the entity known as V'Ger, which was destroying everything in its path as it advanced towards Earth; she succeed in averting the danger and proceeded on her shakedown cruise. The revised specifications of the refitted model of Constitution are listed below :
 
 

Once the Enterprise was through her shakedown cruise successfully the remaining Constitutions where refitted in quick succession. The new ships proved to be more than capable of carrying out their normal exploratory and scientific roles, while in the combat arena they where judged an easy match for the new Klingon K'T'Inga class. The Constitutions continued in service for a further twenty years, and once again the Enterprise set the standard for the rest of the ships to follow. After her shakedown the ship conducted another five year exploratory mission under Admiral Kirk before being transferred to training duties in 2277 under Captain Spock. She continued in this role for a further eight years, and many of Starfleets most successful officers went into space for the first time aboard this ship. In 2285 the Enterprise suffered heavy battle damage while preventing Khan from stealing the Genesis Device; the ship was to be retired at this point, but Kirk and his officers stole her and took her to Genesis to retrieve Captain Spock's regenerated body from the planet. The Enterprise was attacked and crippled by a Klingon Bird of Prey while at Genesis, and was subsequently destroyed by Admiral Kirk shortly after the Klingon crew boarded to take control.

The USS Yorktown was subsequently renamed as the second Starship Enterprise, NCC-1701-A, and assigned to the now Captain Kirk. The Yorktown had recently emerged from a major refit, and the ship suffered many technical problems on her first mission; nevertheless, she went on to serve the remainder of her service life with distinction. The most notable mission of the Enterprise-A where the actions she and the USS Excelsior participated in at the Khittomer conference; as the Enterprise escorted the Klingon Chancellor to the first meeting assassins beamed over to the Klingon ship and killed the chancellor. Kirk and his chief medical officer where arrested and convicted of this crime, and sentenced to life imprisonment on the penal asteroid of Rura Pente; Kirk promptly escaped and took the Enterprise to the conference at Khittomer, preventing another assassination attempt and saving the peace process.

The Enterprise-A went into retirement shortly after this mission. The remaining Constitutions where decommissioned over the next five years as the Excelsior class became available in numbers.