Ok this one has a bit of a story to go with her:
Under the terms of the First Khitomer Accords, Starfleet was required to reduce it's military posture by a substantial margin. One of the ship classes to feel the resulting pinch was the venerable Constitution
class. Already well on the way to retirement, ships of that class could be stood down in considerable numbers, allowing the Federation to quickly make it's treaty quota without sacrificing the Excelsior
class ships which were intended to become the new mainstay of Starfleet operations.
As a result, the bulk of the remaining Constitution
class hulls still in service were systematically retired to the “mothball fleet” scattered among surplus ship depots across Federation space. A few, mostly newer builds with a decade or less on their spaceframes, were retained as training vessels and testbeds for new ship systems.
One such was the USS Eisenhower
, a Block III hull of the Enterprise
sub-class, originally launched in 2285. Tapped in 2297 for testing duty, Eisenhower
was towed to the Luna Shipyard where she was partially dismantled, and then reassembled. Primary changes included swapping out the ship's impulse engines, a reworking of her secondary hull's structural bracing to accommodate a new nacelle pylon placement and the replacement of the nacelles themselves with a hybrid circumfrential/linear configuration that was also somewhat longer then her previous units.
Additionally, the connecting pylon between the hulls was reinforced, thickened and shortened, and the photon torpedo bay was reworked from two side-by side manually operated tubes to a single tube designed for automatic operation. The phasers were replaced with a newer model that, while more energy efficient had less total firepower than her previous system. This effectively reduced the ship's offensive power enough to remain within treaty limits despite the inclusion of a fourth set of phaser banks on the saucer section dorsally and ventrally. The new banks were reoriented 45 degrees off of their original emplacements as a result.
Other changes included an improved M/AM reactor, and a reworking of the ship's science facilities. The total number of operational crew was reduced from the 500+ then commonplace on Constitution
s to just under 400, less than the crew requirement for the class 30 years prior.
The scope of the changes led Starfleet to designate the ship as “lead” of a new subclass. Eisenhower
was rechristened USS Excalibur
while retaining her original NCC designation. She was relaunched in 2299.
The new systems worked mostly as planned. The ship was not quite as capable a combatant as she once was, but her power requirements were roughly 11% less than before the refit, increasing her operational endurance. The changes to the nacelle pylons and the new hybrid nacelle design proved beneficial as well, tightening the ship's warp field substantially, increasing her “dash” speed to Wf 13 [Cochrane scale], and her cruise to Wf 9.5 at the cost of a slight amount of maneuverability.
Starfleet considered the experiment a success, and an additional 5 hulls were refit to the same standard. The Excalibur
subclass remained in service until 2334, when the last ship was again retired. The subclass included the Excalibur,
as well as the John F Kennedy, Midway, Yammamoto, Sel'tarn,