In 2271, the USS Enterprise was selected to be the first ship to undergo a massive refit of the original Constitution class, and went into Earth spacedock for eighteen months of work. Never in Starfleet history, at the time, had 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 Earth 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 shortly thereafter.
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 refit Klingon K’T’Inga class. The Constitutions continued in service, 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 James T. Kirk. By 2285, she had been assigned to Starfleet Academy under the command of Captain Spock. That year the Enterprise suffered extensive 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, NCC-1704, was subsequently renamed as the second starship Enterprise, NCC-1701-A, and assigned to the newly-demoted Captain Kirk. The Yorktown had recently emerged from a major refit and repair following it’s encounter with ‘the whale probe’, and the ship suffered many technical problems, nevertheless, she served Starfleet as the new Enterprise as well as the Enterprise before her.
During the turn of the century the Constitution class proved to be a formidable starship on the frontier in both exploration and combat patrol. However the newer Excelsior Class starships proved to be too much to keep the Constitution class remaining in production. The remaining Constitution Class starships were all refitted to the new design by 2290, and production ceased with 24 starships of the class in service. Over the next 80 years all but six would be retired, decommissioned, destroyed, or lost. The remaining starships provide a varying amount of roles including training vessels, core world patrol vessels and even frontier exploration, well over 100 years after the original Constitution class rolled off the assembly line.
Several projects and proposals from the Starfleet Corps of Engineers have been launched to attempt to relaunch the class with the newest, most updated technologies to preserve the original, iconic design. So far, though, all attempts have proven unsuccessful.