The USS Kongo (NCC-1710) was a Federation starship in service during the late 23rd century.
In 2293, the Kongo was on Neutral Zone patrol during the time Operation Retrieve was proposed. (Star Trek VI: The Undiscovered Country)
Background
This vessel is presumably named after the Japanese battleship from World War II. Its existence and registry is not from dialogue, it was seen only on background artwork. No design was established for the Kongo, it was probably graphically represented by the outline of a movie era refit Constitution-class heavy cruiser.
Although not considered as canon, Franz Joseph's Star Fleet Technical Manual lists the Kongo - with the NCC-1710 registry - as a Constitution-class starship. However, it is likely that--as in the case with Star Trek I--the Technical Manual was used for the references in it. It is plausable to assume that this ship was indeed of the Constitution-class.