The Doctor, Polly, Ben and Jamie find themselves on a moonbase in the year 2070. Housed there is the Gravitron, a device which controls the Earth's weather. But a suspicious plague has erupted among the base's crew, and the Gravitron has been experiencing mysterious faults. The moonbase chief suspects the time travellers are responsible, but the Doctor soon realises that his old foes, the Cybermen, are covertly at work in 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 The Highlanders. When it was determined that The Underwater Menace could not be feasibly made 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 to the schedule as the Second Doctor's new third adventure. However, Emms fell ill, preventing him from accomplishing necessary rewrites on “The Imps”. An amended 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 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, who were now largely viewed as old hat. Shortly after The Tenth Planet finished production, Lloyd approached Pedler about developing a new storyline involving the Cybermen, this time 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 set 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 Return Of The Cybermen” was commissioned on November 18th, 1966. At about the same time, Pedler was made aware that he would have to incorporate the new character of Jamie into his storyline, Jamie having been a last-minute addition to the regular cast during production on The Highlanders. 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 somewhat. At this stage, the Cybermen had personal names, as had been the case in The Tenth Planet, with the lead Cyberman known as Tarn (a name 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 all their future appearances.

Meanwhile, in mid-December, “The Imps” was dropped from the schedule; “The Return Of The Cybermen” took its place as Serial HH. Soon thereafter, it underwent a name change to The Moonbase. (“The Imps” would shortly be abandoned altogether on January 10th, 1967.) It was known at this time that -- due to a break in production at the end of December because of the holiday season -- episodes of Doctor Who would soon be aired just one week after production, a precarious situation at best. On December 1st, the possibility of holding back broadcast of The Moonbase by a week was considered, to restore the delay between recording and transmission to two weeks, but this did not come to pass. On January 10th, the option on Frazer Hines' contract for Serial HH was taken up. At about the same time, Peter Bryant -- who had recently begun assisting Davis in the story editor's position -- briefly took over as producer when Lloyd embarked on a week's holidays.

The director assigned to The Moonbase was Morris Barry, a former repertory theatre actor who had joined the BBC as a floor manager in the mid-Fifties. Barry had been promoted to director by the end of that decade, working on programmes including Z Cars, and had also produced series such as Compact and 199 Park Lane; Davis had served as story editor on the latter.

Filming at the Ealing Television Film Studios took place from January 17th to 20th, with the scenes on the Moon's surface being the major concern. This saw the debut of the new-look Cybermen, who had been thoroughly reimagined by Sandra Reid. Reid had also created their original appearance 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 playing Cybermen who joined the production on January 19th was John Levine who (under the slightly altered surname “Levene”) would play recurring character Sergeant Benton in Doctor Who in the Seventies.

During filming, a small problem arose from the decision to change Benoit's surname from Jules to Roget: 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.

As usual, each episode of The Moonbase was taped in order on Saturdays, beginning on February 4th. The venue for the first three episodes was Doctor Who's regular studio home of Riverside 1. A potentially severe accident occurred during camera rehearsals for part one when the Gravitron prop collapsed just seconds after Troughton had passed underneath it. Fortunately, the actor was not injured and the prop was rebuilt before recording began. Episode three, taped on the 18th, overran its allotted timeslot, forcing the deletion of a scene involving Hobson, Benoit and a Cyberman. This would have revealed that these Cybermen had left Mondas prior to its destruction in The Tenth Planet and had settled on the planet Telos.

Much to Lloyd's disappointment, part three marked the end of Doctor Who's residence at Riverside Studios. The series would now move back to the more cramped and antiquated confines of Lime Grove D, which had housed Doctor Who during its first year in production. Lloyd complained that the inferior quality of Lime Grove's facilities might make it necessary to transfer all film material onto videotape prior to editing. Doctor Who returned to Lime Grove D on February 25th to record episode four; the final scene of this installment had been recorded by director John Davies on the 17th at Ealing as part of filming for the next serial, The Macra Terror.

The difficulties of working in Lime Grove D immediately became apparent when, reviewing the part four footage the next week, Barry 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 due to the need to broadcast it the following Saturday, Barry was forced to edit out this “talkback” as much as possible. Nonetheless, the return of the Cybermen was judged to be a success, and by the start of March, plans were already afoot to bring them back again for Season Five.

• Doctor Who: The Handbook: The Second Doctor by David J Howe, Mark Stammers and Stephen James Walker (1997), Virgin Publishing, ISBN 0 426 20516 2.
• Doctor Who: The Sixties by David J Howe, Mark Stammers and Stephen James Walker (1992), Virgin Publishing, ISBN 1 85227 420 4.
• 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.