The construction of the El Dorado as a class I/class IXA was authorized by Starfleet appropriation on stardate 3220, and she was assigned the registry number NCC-1722. (TOS reference: Star Fleet Technical Manual) In the year 2261, the El Dorado conducted a follow-up visit to the Chyrelkan system. (TOS novel: Renegade) The El Dorado was refit to the Enterprise-subclass specifications, outfitted as an advanced heavy cruiser (CA+), by the 2280s decade. (ST video game: Starfleet Command)