The USS Jenova was a W13 Galaxy-class Federation starship launched in the late 24th century. Her commanding officer was Captain Iviok. The Jenova was nearly destroyed when trying to protect Earth from the Trozonian Empire. (Star Trek: Phoenix-X)
After the construction of the USS Xena and the failed intent on reaching higher warp velocities, Starfleet found usefulness in the third nacelle in that it created a more stable warp field that would withstand some previously harmful spacial phenomenon. Thus the Jenova and a few more vessels were commissioned.