Ok, here's the refit.
The USS Republic. Put in dry dock after taking extensive damage at the 2nd Battle of Chintoka. As a large but old battlecruiser, the Republic spent two years in dock without repair. After that time, Starfleet selected it as the first ship to be part of an Ambassador class modernization program. With Galaxy class starships getting priority upgrades, the Republic was refitted with refurbished Type X phaser array emitters and torpedo launchers from the USS Galaxy, including two small new arrays near the aft shuttlebay. An entirely new deflector dish was installed. Adapted from the Sun Tzu Class, it was selected for its ability to create extremely powerful deflector fields and highly penetrative sensor beams.
Single reactor impulse engines were added to each nacelle pylon, and the pylons themselves were shortened along the Z axis to accommodate the ship's new, sleeker warp field. This, along with a new top speed of warp 9.7, came as a result of new, reshaped warp coils. Overall engine height was adjusted to match the new coils, though a new field emitter ring had to be installed around the circumference of each nacelle. In addition, each nacelle was capped by a new, high compression bussard collector.
An enlarged bridge deck made space for additional subprocessing cores and storage compartments.
Non visible enhancements include included a high capacity shield grid, faster turbolifts, new bioneural circuitry and holodecks.
