James Doohan's favorite episode for its highlighting of the engineering aspects of the Star Trek world.
This is the most effects-heavy episode of the second season. When the series was digitally remastered for its 2007 DVD release, the upgrade required nearly 200 new effects shots.
According to William Windom, he did not enjoy working on the show. He said that William Shatner and Leonard Nimoy were not getting along at the time, which made the set's atmosphere tense. He also said that he felt that the episode was silly so he purposely overacted. It was not until many years later that he realized that his character was a reference to Captain Ahab from Herman Melville's "Moby Dick."
Director Marc Daniels finished this episode in five days instead of the usual schedule of six. Daniels made a bet with the producers that he could finish the episode in five days. When he succeeded, he got a $500 bonus.
This episode marks the first time Scotty is heard cursing in Gaelic. He later utters the same expletive in I, Mudd (1967) and Star Trek V: The Final Frontier (1989).