The series was pitched in a single day to ABC, CBS and NBC. Fox was avoided due to the concept's overt similarities to their hit series Los expedientes secretos X (1993). Each network received a classified "briefing book" written by Zabel and Friedman, wrapped in plain brown paper, which warned that by opening the package they accepted the high level clearance it implied and the full penalties set by the US government for unauthorized disclosure. By the end of the day, two offers had been made and the series went to NBC.
A book covering the series was published as part of Obverse Books The Silver Archive series of Cult TV guides in April 2020.
The series takes place from May 1, 1960 to June 22, 1967.
Eric Close (John Loengard) and the narrator Gregory Harrison (Old John Loengard) are the only actors to appear in all 20 episodes of the series. In second place is Megan Ward (Kimberly Sayers), who appeared in every episode except Strangers in the Night (1997).
Conor O'Farrell (Lt. Commander Phil Albano) previously played Professor Jeff Carlson in Little Green Men (1995), which also involved the Roswell UFO Incident.