The USS John Muir (NCC-1732) was a 23rd century Federation starship operated by Starfleet.
In 2293, the John Muir was undergoing a refit at Starbase 24 during the time Operation Retrieve was proposed. (Star Trek VI: The Undiscovered Country)
The John Muir was named after the renowned environmental advocate who was largely responsible for the creation of Yosemite National Park. The ship itself was not mentioned in dialog, but was listed on a starship status display that was seen on the Enterprise-A. The information came from the Star Trek Concordance.
According to a ship listing included in the plans, and not seen in the extended cut of the movie, the ship's commanding officer was S.C. Jaffe. The ship's captain was named after the sixth movie's second unit director Steven-Charles Jaffe. [1]