- Actor-Inspired Element: It was Ingrid Pitt's idea for Solow to fight the Myrka.
- Cast the Runner-Up:
- Ian McCulloch was originally considered for Vorshak before being cast as Nillson.
- Norman Comer was first booked to play Tarpok before being cast as Icthar.
- Creator Backlash:
- Johnny Byrne was very unhappy with how the episode turned out, from Eric Saward's re-writes to the design of the Seabase to the Myrka.Nowhere did I describe it (the Myrka) as a four-legged beast on loan from Panto-Horses-Are-Us.
- He also stated that the base looked nothing as he envisioned it:I was very specific in my description of the base — rusting, leaking, virtually forgotten by all except those on board — the atmosphere and look was something like Alien with the Myrka essentially a lurking deadly presence waiting to reveal itself.
- Peter Davison was also dissatisfied with the story, citing it as one of the examples of weak scripts that led him to leave the show.
- Johnny Byrne was very unhappy with how the episode turned out, from Eric Saward's re-writes to the design of the Seabase to the Myrka.
- Fan Nickname: Fans dubbed this story "Warriors on the Cheap".
- Fatal Method Acting: Averted. Peter Davison contracted hypothermia from the stunt that required him to fall off a high bridge into a pool of water. Due to budget, they didn't heat the water and it was ice cold. The actors in the Myrka costume, on which the paint hadn't dried, also reported becoming light-headed and dizzy from the fumes as they were effectively sniffing glue.
- Old Shame: Everyone involved cites this as an example of how not to do a Doctor Who story.
- Recycled Script:
- The plot bears striking similarities to "The Tenth Planet". Both feature the Doctor and his companions accidentally arriving at an isolated military base and being mistaken for spies, and in both stories the Doctor's warnings go unheeded until the base is besieged by an alien threat. In both there is a section of the story where the alien invaders seize the bridge and the Doctor is forced by circumstances to stand by without interfering for a time.
- Johnny Byrne drew inspiration from the Space: 1999 episode "Guardian of Piri", which he script-edited.
- Stunt Casting: Hammer Horror veteran Ingrid Pitt as Doctor Solow. Her appearance is mostly memorable due to her character's death scene being one of most embarrassing moments in all of science fiction.
- Troubled Production: Legendarily so. Margaret Thatcher announced an election and all the studio space was given to the coverage, meaning this serial lost two weeks of valuable production time. Thus most scenes were shot in one take and much of it was not even rehearsed. There were many rewrites, partially to Bowdlerise/remove political subtext that might influence the election, and partially due to Ian Levine being obsessed with preventing Series Continuity Errors. The Myrka costume was completed only half an hour before filming and the paint and glue on it weren't dry it visibly smears on the sets as it staggers around, the actors inside the costume being light-headed from the fumes (the director, Pennant Roberts, had begged John Nathan-Turner to let him drop it). Peter Davison had No Stunt Double and got tossed into an ice-cold pool of water (after being assured that it was warm) because the BBC didn't have the budget to afford warm water. The writer wanted the base to be dark and the sets had been built with that in mind, but Lawful Stupid BBC studio engineers insisted on lighting it as if it was on the surface of the sun, in line with regulations intended for chat shows. In the end, this story deeply stained the show's reputation, and BBC execs used the Fight Scene Failure of the Myrka sequence as grounds to cancel the show.
- What Could Have Been:
- Steven Berkoff, BRIAN BLESSED, Martin Jarvis, Patrick Stewart, David Warner and Peter Wyngarde were considered for Vorshak.
- Honor Blackman was considered for Solow.
- Ian Holm, and Ian McKellen were considered for Nillson.
- Helen Mirren and Catherine Schell were considered for Preston.
- Donald Sumpter was considere for Bulic.
- In the original script, Preston and Commander Vorshak survived the massacre at Seabase Four.
- Doctor Solow and Preston were at first male, but Pennant Roberts changed their gender.
- The Myrka was originally supposed to be just a much bigger and stronger Sea Devil. However, the production team did not feel that this was suitably impressive, and instead had it redesigned into a quadrupedal beast. Considering the Myrka's reputation as one of, if not the worst-realised monster in the show's entire history, odds are they'd have been better off sticking with the original incarnation.
- You Look Familiar: Ingrid Pitt had previously played Queen Galleia.
Trivia / Doctor Who S21 E1 "Warriors of the Deep"