The registry number of the USS Enterprise in the original "Star Trek" series is NCC-1701.
The ship is a Constitution-class starship and serves as the main setting of the original series, which aired from 1966 to 1969. Captain James T. Kirk commands it during its famous five-year mission, alongside Spock, Dr. Leonard McCoy, and the rest of the crew.
The number belongs specifically to the original Enterprise, not every starship carrying the name. After the ship is destroyed in Star Trek III: The Search for Spock, Kirk receives a replacement designated NCC-1701-A. Later ships use additional suffixes, including NCC-1701-B, NCC-1701-C, NCC-1701-D, and NCC-1701-E.
The NCC designation was inspired partly by American aircraft registration codes. The number 1701 was developed by designer Matt Jefferies, who considered it a visual identifier for Starfleet's seventeenth starship design and rejected digits that could be confused on screen. NCC-1701-D is therefore a different vessel associated with Star Trek: The Next Generation.