At first, the show was intended to be a realistic portrayal of the near future. When the show suffered low ratings, however, it was allowed to go in a more fantasy-oriented direction that included stories about aliens, lost civilizations, and even the Greek god Neptune.
During the third season, several episodes were shown out of order. As a consequence, the character of Lt. Brody dies in one episode and then reappears in a later one. Similarly during the first season the episode in which Admiral Noyce is appointed UEO Secretary General aired after two episodes were broadcast with him already in this position.
Roy Scheider disliked the direction of the show in the second season, gearing it towards more heavy science-fiction elements and requested to be released from his contract. NBC partially obliged, requiring him to appear in only three third season episodes.
When guest star William Shatner appears on a viewscreen, the ID code at the bottom reads "JTK NCC1701". This stands for "James T. Kirk", Shatner's character on Star Trek (1966) and the registry number of the U.S.S. Enterprise, Kirk's ship.
Jonathan Brandis (Lucas Wolenczak) is the only actor to appear in all 57 episodes of the series. In second place are Don Franklin (Commander Jonathan Ford) and Ted Raimi (Lt. Timothy O'Neill) who appeared in every episode except for "And Everything Nice".