The Doctor, Polly, Ben and Jamie find themselves on the Moon in the year 2070. When Jamie is injured, his friends seek help at a nearby Moonbase, which houses the weather-controlling Gravitron. However, a plague has erupted amongst its crew, and the Gravitron has started experiencing mysterious faults. Hobson, the Moonbase commander, begins to suspect that the time travellers are responsible for the crisis. But the Doctor soon discovers that the culprits are his old foes, the Cybermen, who are preparing to seize control of the Gravitron as part of a new attempt to invade the Earth.

The two stories originally set to follow Patrick Troughton's debut serial, The Power Of The Daleks, were The Underwater Menace and then The Highlanders. When concerns arose about the feasibility of making The Underwater Menace on a Doctor Who budget, it was dropped from the schedule; The Highlanders was moved up one slot and William Emms' “The Imps” was added as the Second Doctor's third adventure. However, Emms then fell ill, preventing him from accomplishing necessary rewrites on “The Imps”. A revised version of The Underwater Menace therefore returned to the schedule in its place, with “The Imps” now intended to follow it.

Meanwhile, the Cybermen had debuted on Doctor Who in The Tenth Planet, the final serial to feature William Hartnell's First Doctor. The monsters, created by Kit Pedler and story editor Gerry Davis, had proved very popular, and producer Innes Lloyd hoped that they might make worthy successors to the Daleks, whom he viewed as less sophisticated. Shortly after production finished on The Tenth Planet, Lloyd approached Pedler about developing a new storyline involving the Cybermen. He suggested that this should be set on the Moon to tap into the interest in the burgeoning space race between the United States and the Soviet Union. To save on costs, Davis wanted the new adventure to take place predominantly on one large set, with just a handful of smaller subsidiary sets and a limited supporting cast; this would be a formula often repeated in forthcoming seasons.

The nameless status of the Cybermen would subsequently become the norm

“The Return Of The Cybermen” was commissioned on November 18th, 1966. At about the same time, Pedler was made aware that he would have to modify his storyline to incorporate Jamie McCrimmon, a character introduced in The Highlanders whom the production team had decided to retain as a companion. Pedler sought to minimise Jamie's impact on “The Return Of The Cybermen” by leaving him unconscious for much of its length, but Davis -- who worked closely with Pedler on the scripts -- would later expand the new companion's role. At this stage, the Cybermen had personal names, as had been the case in The Tenth Planet, with the lead Cyberman known as Tarn (which Pedler had also used in the earlier serial) or Kron. Eventually, any such references were eliminated, and the nameless status of the Cybermen would become the norm in their subsequent appearances.

By the end of November, it was known that, come the broadcast of The Underwater Menace in January 1967, Doctor Who would be in the precarious situation of recording episodes just one week prior to transmission. As such, on December 1st, consideration was given to inserting a one-week hiatus before airing the first episode of “The Imps”, although this did not come to pass. Then, on December 14th, “The Imps” was dropped from the schedule. It was replaced by “The Return Of The Cybermen” which, soon thereafter, was renamed The Moonbase. On January 4th, “The Imps” was abandoned altogether.

As 1967 dawned, the Doctor Who production team gained a new member in the form of Peter Bryant, who was supporting Davis as story editor. Lloyd was starting to think about moving on from Doctor Who, and Bryant was seen as a potential replacement; as such, Bryant briefly took over as producer when Lloyd embarked on a week's holidays in mid-January.

The director assigned to The Moonbase was Morris Barry. He was joined on the serial by costume designer Sandra Reid, who had created the original Cyberman costumes for The Tenth Planet. The production team wanted the monsters to look more robotic and streamlined, and so Reid crafted three alternative designs from which Lloyd and Barry made their selection. Amongst the extras cast as Cybermen for The Moonbase was John Levine who -- as John “Levene” -- would play recurring character Sergeant Benton for several years beginning with 1968's The Invasion. Meanwhile, portraying the scientist Jules Fauré was Victor Pemberton; some weeks later, he would join Doctor Who as an assistant story editor.

Filming at the BBC Television Film Studios in Ealing, London took place from January 17th to 20th. Scenes on the Moon's surface were the chief concern, while model shots were also completed on the last day. Rehearsals for the studio sessions then began, at which time it was realised that both of the French scientists -- Fauré and Benoit -- had been given the first name Jules. It was agreed that the latter would now become “Roger” Benoit. However, the name plate for actor Andre Maranne's outfit had already been prepared bearing the initial ‘J’, and there was no way to change it in a timely manner. To compensate, Maranne was given a neckerchief to wear to cover the offending letter.

During camera rehearsals, the Gravitron prop collapsed just seconds after Patrick Troughton passed under it

As usual, each episode of The Moonbase was taped on consecutive Saturdays, beginning on February 4th. The venue for the first three installments was Doctor Who's regular production home of Riverside Studio 1 in Hammersmith, London. A potentially serious accident occurred during camera rehearsals for Episode One, when the Gravitron prop collapsed just seconds after Troughton had passed under it. Fortunately, the actor was not injured and the structure was rebuilt before recording began.

With the Cybermen's visual appearance having been updated, it was decided that a new vocal effect should also be employed for The Moonbase. Voice artiste Peter Hawkins was given a modified dental palate -- originally designed for use by patients who had undergone the surgical removal of their larynx -- which produced electronic sounds just by shaping the mouth and lips appropriately. This method was used for the first time on Episode Three, recorded on February 18th. Unfortunately, the persistent vibration induced by the device gave Hawkins headaches and made him nauseous. This installment ran long, forcing the deletion of a scene involving Hobson, Benoit and a Cyberman. It would have revealed that the Cybermen on the Moon had left Mondas prior to its destruction in The Tenth Planet and had since settled on the planet Telos.

Much to Lloyd's disappointment, Episode Three marked the end of Doctor Who's residence at Riverside Studios. The series now moved back to the more cramped and antiquated confines of Lime Grove Studio D in Shepherd's Bush, London, which had housed Doctor Who during its first year in production. Episode Four was taped there on February 25th, although the final scene had been recorded on the 17th by director John Davies, as part of filming at Ealing for the next serial, The Macra Terror.

The difficulties of working in Studio D immediately became apparent. When Barry reviewed the Episode Four footage the following week, he discovered that the sound equipment had picked up some of the chatter from the floor manager's headphones. Since there was no possibility of the episode being rerecorded -- given that it would be broadcast the following Saturday -- Barry was forced to edit out the “talkback” as much as possible. Nonetheless, the return of the Cybermen in The Moonbase was judged to be a success and, by the start of March, plans were already afoot for a sequel.

• Doctor Who Magazine #322, 16th October 2002, “Archive: The Moonbase” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who Magazine Special Edition #4, 4th June 2003, “Good Vibrations” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who: The Complete History #9, 2016, “Story 33: The Moonbase”, edited by John Ainsworth, Hachette Partworks Ltd.
• Doctor Who: The Handbook: The Second Doctor by David J Howe, Mark Stammers and Stephen James Walker (1997), Virgin Publishing.
• Doctor Who: The Sixties by David J Howe, Mark Stammers and Stephen James Walker (1992), Virgin Publishing.