. As the Doctor was transitioning from the third to the fourth incarnations, changes were also occurring in the production department of
Doctor Who.
Barry Letts, who had been the producer since the second
Jon Pertwee serial in 1970, was leaving the series, but would stay on to cast the part of the new Doctor as well as produce this debut serial. Letts would be succeeded for the next story by
Philip Hinchcliffe, who trailed him on this story.
Terrance Dicks, who had worked on the series as a script editor since 1968, Allister Bowtell. These elements helped the audience with the transition between actors.
Casting It was known beforehand that Jon Pertwee would be leaving his role as the Third Doctor and that a new
Fourth Doctor would need to be cast for the part.
Tom Baker had previously had major parts in several films, including
Nicholas and Alexandra (1971) and
The Vault of Horror (1973), but had found himself unemployed as an actor and working in construction at the time. He had written to Bill Slater, the Head of Serials at the BBC, asking for work. Slater suggested Baker to
Doctor Who producer
Barry Letts, who had been looking to fill the part. Letts saw Baker's work in
The Golden Voyage of Sinbad (1973) and hired him. Baker would continue in his role as the Doctor for seven seasons, longer than any other actor.
Nicholas Courtney and
John Levene reprised their roles as
Brigadier Lethbridge-Stewart and
Sergeant Benton respectively. Levene had started his role with the
Second Doctor story
The Invasion (1968) as a member of the military organisation
UNIT (the United Nations Intelligence Taskforce). Courtney started earlier in the same year in
The Web of Fear, with his character's rank being a colonel. They, along with Sladen, would be the transition cast to carry through from the Third Doctor to the Fourth Doctor, though this would be the only UNIT story for the twelfth season. The Earth-based stories involving UNIT, which had regularly featured in the Third Doctor's period, were introduced partly as an effort to reduce production costs when the series moved into colour by
Peter Bryant and
Derrick Sherwin, the show's previous producer and script editor, as well as to base the series more on
The Quatermass Experiment (1953). Edward Burnham portrays Professor Kettlewell, the wild-haired, bespectacled
boffin who creates the titular K1 robot. Along with Courtney and Levene, Burnham had also appeared in
The Invasion, where he played another scientist, Professor Watkins. The part of the K1 robot is played by
Michael Kilgarriff who had played another robotic part in
The Tomb of the Cybermen (1967), the
Cyberman Controller.
Patricia Maynard is cast in the part of Miss Hilda Winters, the director of the National Institute for Advanced Scientific Research. Miss Winters' assistant, Arnold Jellicoe, is played by Alec Linstead. Linstead had played the part of Sergeant Osgood—a member of the technical staff at UNIT—in
The Dæmons (1971).
Filming This was the first serial to be produced for the season. This was also the first
Doctor Who serial to have its location material shot entirely on
videotape using
outside broadcasting facilities, as opposed to the more usual
BBC television drama practice of the time of shooting studio interiors on videotape and location exteriors on
16 mm film. This was due to the large number of video effects involving the eponymous robot required in exterior scenes (shot at the then BBC Engineering Training Department at
Wood Norton, Worcestershire), which were easier and more convincing to marry to videotape than to film. The team had learned that lesson during the previous season's
Invasion of the Dinosaurs. The Wood Norton facility was chosen for location shooting because it had an underground bunker, which director Christopher Barry felt would be suitable for the entrance to the underground complex in the story; however, they were refused permission to shoot in that area. == Broadcast and reception ==