The Excalibur was ordered in an initial block of four, constructed in parallel between 2234 and 2236: Excalibur, Enterprise, Curtana, and Durandal. The ships proved to be of major tactical benefit to Starfleet's general roster, being both more heavily shielded than the Newton and substantially more dangerous. After a year-long shakedown that resolved problems with the new torpedo launchers and further streamlined the thruster assemblies a further order of eight ships were made: Tizona, Caladbolg, Joyeuse, Kusanagi, Clarent, Hauteclere, Tyrfing, and Hrunting. All were commissioned in 2238 and entered service the following year.
The outbreak of open war with the Klingon Empire in the spring of 2240 threw Starfleet on the back foot, and further orders of starships with secondary tactical roles were suspended. Instead in 2241 a further six Excalibur-class vessels were ordered and entered production, those being Dyrnwyn, Damocles, Dainsleif, Gram, Naegling, and Fragarach. The crash-builds saw the ships launch in late 2243 in time for the counteroffensive of early 2244.
After the war the surviving Excalibur-class ships faced an uncertain future. Lacking the facilities to participate in the rebuilding efforts they were assigned to suppressing the surge in piracy caused by the depletion of Starfleet's patrol roster and flying the flag near contested borders with the Tholian Assembly and Gorn Hegemony. They finally entered their second stage of life in the 2250s when a recovered Starfleet turned its attention back to beyond its borders. The Pathfinder Missions were designed to use the Excalibur's range and speed to chart over a hundred light years beyond the boundaries of Federation space.
The Excalibur would become the most common exploration ship in the Starfleet roster for some time, if not the foremost scientific platform. It provided a vital service in identifying lifebearing stars, cataloguing stellar phenomena, and carrying out First Contact with a number of new civilizations. In the era in which the Federation was constantly discovering novel new demonstrations of heretofore-unknown sciences it was the Excalibur that reported the first sightings.
Unfortunately this meant that the Excalibur was the first ship subjected to its discoveries, and this often resulted in serious casualties and total ship losses. The Curtana and Tyrfing were destroyed during the infamous multitronic incident, Dainsleif was digested during the first encounter with massive unicellular lifeforms, the crew of the Damocles were killed by macroscopic parasites, and the Hauteclere faced the ultimate indignity of being used to prop up the Terran Empire for an extra hundred years in the mirror universe.
The high attrition rate suffered by the Excalibur-class during the Pathfinder Missions was a major factor in the codification of the 'explorer' as a specific design brief. The stunning performance of the Enterprise in the course of its duties was considered the result of the spectacular brilliance of its command crew and their ability to accomplish novel solutions with limited resources. Future long-term missions beyond resupply would be traditionally accomplished by ships specifically designed for the task.
Regardless of losses the Excalibur entered its fourth decade with enough hulls to justify a refit which replaced or improved the shields, onboard laboratories, warp coils, phasers, and built out the torpedo systems for heavier Type-4 warheads. The improvement in capabilities and performance kept the ships in service for another three decades before larger vessels and improvements in basic technology made keeping the Excalibur active an increasingly costly proposition in personnel and upkeep.
Only two examples of the class survived the scrapyard, both selected for repair and preservation. The Joyeuse, which has been restored to its 2240 configuration, was initially part of the Andorian Imperial War Museum but later centralised and consolidated with other vessels at the Federation Fleet Museum. The Enterprise-A remained moored at Utopia Planitia after its decommissioning in administrative limbo until it was repaired and the impulse drive reactivated for a ceremonial flypast during the launch of the Enterprise-B. It was subsequently moved to a lunar orbit as an open museum until 2370 saw it moved under warp tow to the Federation Fleet Museum.
