Verity Lambert, although credited as producer on the first two stories of the new season, was in the process of handing over to her successor John Wiles during the making of Galaxy 4 and had almost completely relinquished her responsibility for the series by the time that Mission to the Unknown went into studio.
Wiles quickly developed a good working relationship with story editor Donald Tosh, himself a relative newcomer to the production team. The two men found that they had very similar ideas about the direction in which the series ought to be steered: both wanted to see it becoming more adult and sophisticated. The fruits of this approach can perhaps be best appreciated in The Myth Makers and The Massacre of St Bartholomew's Eve, although the epic The Daleks' Master Plan - a carry-over from Lambert's time - was also unusually grim and horrific in content, making a marked contrast to the Daleks' previous major outing in The Chase.
William Hartnell - who had always regarded Doctor Who as primarily a children's series and, as the only one left of the original team, saw himself in some ways as the guardian of its true spirit - greatly disliked this new approach. This resulted in a number of clashes between actor and producer. Indeed, Wiles seriously considered having Hartnell written out and replaced after scenes in The Celestial Toymaker in which the Doctor becomes invisible for a time. In the end however Gerald Savory, Donald Wilson's successor as Head of Serials, renewed Hartnell's contract against Wiles' wishes. Wiles resigned shortly afterwards; and, in what Wiles would later describe as an unnecessary act of loyalty, Tosh decided to go as well.
Tosh was in fact the first to leave, handing over to his successor Gerry Davis part-way through the making of The Massacre of St Bartholomew's Eve. Wiles then gave way to new producer Innes Lloyd, who accepted the job only reluctantly as he had no prior interest in science-fiction.
Lloyd and Davis were never on the best of terms but nevertheless formed a very effective team on the series. After working through a number of stories essentially inherited from Wiles and Tosh - which, possibly because of the change of team, ended up being rather lacklustre - they started to introduce some new ideas of their own, giving Doctor Who a fresh impetus and paving the may for more major changes to come.
Due in large part to the transition of producers from Verity Lambert to John Wiles to Innes Lloyd, and the accompanying change of story editors from Donald Tosh to Gerry Davis, the stories of Doctor Who's third season were amongst the most varied in terms of subject, setting and style of any in the series' history. Unfortunately, particularly toward the end of the season, they also tended to be somewhat varied in terms of quality and their degree of appeal to the viewing audience. The War Machines, however, saw Lloyd and Davis really starting to make their own mark on the series.
Lloyd had been keen from the outset to update the style of Doctor Who - which in his opinion had previously been rather old-fashioned and whimsical - and to make the Doctor's adventures more action-orientated and 'gutsy'. To this end, he and Davis recruited an unofficial scientific adviser to the series in the person of Dr Kit Pedler, whose first real contribution was to provide the basic story idea for The War Machines.
Lloyd also took this opportunity to change the image of the Doctor's companions. The original intention had been that Dodo should continue as a regular, with a new character called Richard, or Rich for short, brought in to replace Steven, following his departure in The Savages. Eventually, however, Lloyd decided that Dodo should also be written out, paving the way for the introduction of a completely new male and female companion team: seaman Ben Jackson and secretary Polly Wright (whose surname was never given on screen) - two up-to-date, 'swinging sixties' characters very much in line with the aim of bringing a greater degree of realism to the series.
The following season would see the production team continuing to mould the series to their preferences - a process that would involve undoubtedly the most momentous change so far.