Editing Constitution Class (section)

===History ===

The Constitution-class lineage was launched some time prior to 2245, and served as Starfleet's front-line vessels for the rest of the century. The Constitution-class also served as a mighty deterrent to both the Klingon Empire and the Romulan Star Empire, several times taking part in combat actions which determined the fate of the entire Federation if not the Alpha Quadrant itself. (Star Trek Encyclopedia)

In 2267, there were around twelve2 Constitution-class starships in the fleet. (TOS: "Tomorrow is Yesterday") These included the NCC-1700, the USS Constellation, the USS Defiant, the USS Enterprise, the USS Excalibur, the USS Exeter, the USS Hood, the USS Intrepid, USS Lexington, and the USS Potemkin.

The most famous Constitution-class starship was the USS Enterprise (NCC-1701), launched under the command of Captain Robert April in 2245. The Enterprise gained its reputation during its historic five year mission (2265-2270) under the command of Captain James T. Kirk. (VOY: "Q2")

In 2266, on stardate 1709, the Enterprise was instrumental in preventing a war between the Federation and the Romulan Star Empire. When a Romulan Bird-of-Prey crossed the Romulan Neutral Zone and destroyed several Earth Outpost Stations, Captain Kirk barely managed to outwit the enemy commander and stop his vessel from returning to Romulus and reporting on the Federation's weakness. (TOS: "Balance of Terror")

In late-2268, Excalibur, Hood, Lexington, and Potemkin took part in the disastrous testing of the M-5 computer, which had been placed in control of the Enterprise. The Excalibur was severely damaged, with all hands lost. The Lexington also was brutally assaulted by the M-5 computer when the unit became unstable. (TOS: "The Ultimate Computer") Later that year, Defiant responded to a distress call from an unexplored sector of space, claimed by the Tholian Assembly. Shortly upon entering the region, the Defiant crew began experiencing sensory distortion, and insanity quickly spread throughout the ship. The ship's surgeon was unable to determine what was happening, and eventually the insanity induced by the phenomenon led the crew to kill each other.

Three weeks later, Starfleet ordered the Enterprise to mount a search mission to locate the Defiant. On stardate 5693.2, the Enterprise located her adrift, lost between universes in a space warp. As a result of a later phaser exchange between the Enterprise and several Tholian vessels, a hole was created through the spatial interphase, pushing the Defiant into the mirror universe. (TOS: "The Tholian Web") 

Unknown to history in the "prime" universe, the Defiant emerged in the 22nd century mirror universe, where the Tholians of that universe had created the interphase rift by detonating a tricobalt warhead within the gravity well of a dead star. (ENT: "In a Mirror, Darkly") The Defiant would seemingly go on to play a major role in Empress Sato's rule over the Earth. (ENT: "In a Mirror, Darkly, Part II")