The USS Enterprise (NCC-1701-M) was a Constitution-class starship museum, a tribute to the original USS Enterprise, launched in 2306. The "M" in the registry stood for museum. Commander Kirk, James Kirk's nephew, was her commanding officer.
In 2306, Captains John Harriman, Nyota Uhura and Pavel Chekov gathered to commission the museum when a beacon in orbit of the planet Gateway, home to the Guardian of Forever, activated, indicating someone had broken through the defense system. The Enterprise-M investigated, with Harriman, Uhura and Chekov beaming down alongside two Enterprise-M personnel. (Star Trek: Of Gods and Men)