The USS Endeavour (NCC-1895) was a Federation starship in service in the late 23rd century.
The Endeavour was on a deep space exploration mission near Klingon territory in 2293. It was among the starships that would have been assembled for the abandoned assault code-named Operation Retrieve, which would have rescued Captain James Kirk and Doctor Leonard McCoy from Qo'noS in 2293. (Star Trek VI: The Undiscovered Country)
Appendices
Background
This starship and registry was not referenced in dialog. This vessel appeared in the plans for Operation Retrieve presented by Colonel West. Besides the USS Excelsior and the USS Springfield, the Endeavour and five other starships were graphically represented by the outline of a movie era refit Template:ShipClass vessel.
From this, the Star Trek Encyclopedia lists the ship as a Constitution-class vessel.
The Endeavour was probably named for the HMS Endeavour, specifically, the HM Bark Endeavour commanded by Lieutenant James Cook in his voyage of exploration in the Pacific from 1768–1771, and the NASA space shuttle Endeavour.
Apocrypha
The Star Fleet Technical Manual includes a Template:ShipClass Endeavour, with a registry of NCC-1716, in service in the mid 23rd century.
The Pocket TOS Errand of Vengeance novel Killing Blow features a USS Endeavor engaging Klingon forces at the Battle of Donatu V in 2245. This Endeavor was referred to as an Icarus-class starship in Errand of Fury: Seeds of Rage.