Constitution Class starships were brought into service in the year 2245 by Starfleet as heavy cruisers. These ships were designed with the first duotronic computer systems invented by Richard Daystrom two years earlier. This type of computer system was used by Starfleet and throughout the Federation for over 90 years. As of 2267, only twelve ships of this class had been built. Of the original twelve cruisers, the most famous is the USS Enterprise, NCC-1701. Under the command of James T. Kirk, Enterprise became the "flagship" of Starfleet. With newer technologies and innovations available, Starfleet made a decision in about 2269 to radically refit the Constitution Class, beginning with the Enterprise. The class would continue to serve in the refit design into the 24th Century.
| CONSTELLATION | NCC-1017 |
| CONSTITUTION | NCC-1700 |
| DEFIANT | NCC-1764 |
| EAGLE | NCC-956 |
| ENTERPRISE | NCC-1701 |
| ENTERPRISE | NCC-1701-A |
| EXCALIBUR | NCC-1664 |
| EXETER | NCC-1672 |
| FARRAGUT | NCC-1647 |
| HOOD | NCC-1703 |
| INTREPID | NCC-1631 |
| LEXINGTON | NCC-1709 |
| POTEMKIN | NCC-1657 |
| REPUBLIC | NCC-1371 |
| YORKTOWN | NCC-1717 |
NOTE: In the editor's note on Page 572 of the Star Trek Encyclopedia, the following is stated relating to Enterprise-A and Yorktown:
(Gene)Roddenberry (creator of Star Trek) reportedly suggested that the second Starship Enterprise, NCC-1701-A, launched at the end of Star Trek IV, had previously been named the Yorktown, since seems unlikely that Starfleet could have built an all-new ship so quickly. If this was the case, the Yorktown may have made it safely back to Earth and been repaired and renamed, or perhaps there was a newer, replacement Yorktown already under construction at the time of the probe crisis.
