According to Frazer Hines, Sally Faulkner's skirt kept getting blown up around her neck whilst climbing up the rope ladder to the helicopter. To avoid the same thing happening to his kilt, he remembered reading somewhere that The Queen had lead weights sewn into the hem of her skirt to stop this from happening to her. It so happened that Frazer's dresser was a keen fisherman, who sewed some lead weights into his kilt.
This episode was wiped by the BBC and no copy of it is known to exist. Off-air audio recordings by fans and the original shooting script were used to recreate an animated version to complete the story for DVD release.
Coincidentally, this episode was originally broadcast on the fifth anniversary of Doctor Who (1963).
Sheila Dunn, director Douglas Camfield's wife, who was the voice of the computer in episode 1, is the telephone operators voice in this episode.
This episode was watched by 6.4 million viewers on its original transmission.