Oh the Federation class… where did it all go wrong.
The Federation class was a clear and simple attempt to turn Constitution-derived technology into a larger, more combat oriented vessel. Whilst the ship was not as huge as the bloated and angular Eaves-Kurtzman ships the Constitution derivatives replaced, it was intended to be better armed, better shielded and far faster than anything built before. Sporting an enlarged Constitution secondary hull, noticeably featuring bow and stern deflector arrays, connected to a thickened primary hull by way of a standard Constitution neck the ship rather recognisably sported three Warp Nacelles, a trait rarely seen in Starfleet vessels.
Whilst the most recent tri-nacelle design, the Niagara class, uses the nacelles for a tightened warp geometry, allowing increased economy and performance, the Federation class does not. The two nacelles connected to the secondary hull are intended to be the primary warp drive when the ship is together, with the central nacelle connected to and only intended to propel the saucer at Warp Speeds. The reason this was done was admittedly rather ahead of its time, in that the Federation class was intended to be able to detach its saucer, send it off on a mission and then reattach it, effectively a precursor to the Multi-vector assault mode seen on the Galaxy, Ross and Prometheus class vessels. The problem was down to the use of a standard Constitution connecting dorsal, making reattachment incredibly difficult for even the most skilled helmsmen.
The problems did not end there. Due to the requirement for the saucer to be a fully functional ship in its own right (in fact the saucer was of greater tonnage than the Saladin class, a full Destroyer) the ship required not one but two warp cores. These cores were meant to be run simultaneously, powering the ship and giving it an incredible energy reserve when in combat. Unfortunately these were also incredibly hard to synchronise, leading to power surges, conduit failures and an emergency Warp Core Ejection essentially straight out the main shuttlebay by the USS Entente in one case. These flaws ultimately ensured that these ships, despite their incredible firepower, were ultimately white elephants, and 8 of the planned 10 ships would be cancelled in favour of a third batch of Constitution class ships.
As specified above, only two ships of the class would ever be constructed, USS Federation and USS Entente, in the early 2260's. Neither would ever see combat, both spending most of their time in the Sol system as propaganda pieces. Whilst the idea of refitting them to TMP Specifications would be floated, it would ultimately be cancelled. Both were ultimately decommissioned in 2286, returning to San Francisco to be ripped apart. Notably several components from the Entente would go to the USS New Jersey, allowing her to remain in good condition without a full refit. Consequently two plaques can be found commemorating the failed ships aboard the New Jersey in the Fleet Museum, where she resides today on display.