Anna Reid (Nurse Crane) would appear later as the Plasmavore vs the Tenth Doctor (David Tennant).
A line of dialogue referring to Ace losing her virginity was removed from the script. The novels would reveal that Ace slept with Glitz when he came to Ice World.
Although there are several references in the story to the Norse belief in a final battle at the end of the world, the word Ragnarok was removed from the script to avoid confusion with the Gods of Ragnarok from the previous season's The Greatest Show in the Galaxy.
This is the only Doctor Who (1963) serial from its 26-year run to be set during the Second World War, although themes from the war had influenced earlier storylines.
The ULTIMA machine was based on the Enigma machine.