Fields was played by John Arndt, apparently a regular extra during TOS Season 1. He had previously played murdered Crewman Sturgeon in TOS: "The Man Trap". Although not referenced on screen, Paul Schneider's script for "Balance of Terror" named this character (along with Brenner) as a phaser specialist. His later character appearances were all unnamed. Assuming they were all the same character, Mr. Fields might have been a career generalist (similar to Mr. Kyle and Mr. Leslie) since he appeared in a command division yellow jumpsuit in "Balance of Terror," a command yellow officer uniform in "Dagger of the Mind," and red security uniform in "Miri."