continuing. Lambert brought on Derek Martinus to replace Pinfield. Martinus had recently completed the BBC's internal directors' course, and had no previous experience leading a television production. Having only seen a few episodes of Doctor Who, Martinus reviewed some of the previous stories with Lambert; he found them disappointing, which shocked Lambert, but stated that he wanted to aim for higher standards. Pinfield was still actively directing as Martinus began, and continued to work alongside him throughout the first week. After Pinfield's departure, Martinus prepared his own camera scripts for the studio production. Galaxy 4 was Pinfield's final work for Doctor Who and the BBC, though he remained uncredited on the broadcast version; he retired from active television production shortly thereafter. Casting and characters The Chumblies were named from the combination of the words "chum" and "friendly". Production designer Richard Hunt created the Chumblies. Four robots were made, each about in height and consisting of three stacked domes made of fibreglass. Various stick-like appendages could be attached to the robot between the base and second dome, and these could be moved by the performer inside. A ring of small domes in the shape of rocket engine nozzles surrounded the base of each robot, hiding the casters on which the costume moved as well as imitating the propulsion units of the mechanoid. The four warthog-like Rill costumes were made of grey-green painted fibreglass and latex. The costumes were largely immobile, although the performer inside could move the arms. To simulate the ammonia atmosphere the Rills breathed, dry ice fog was used. Anthony Paul was hired to voice the Rills, but a late scheduling conflict prevented him from doing so; he was replaced by Robert Cartland. The Drahvins were originally named Dravians, and written as a race of male soldiers; during casting, which took place in early June 1965, Lambert suggested that their gender be switched to female, in part as a nod to the emerging women's liberation movement and to better emphasise their attractiveness. Emms concurred with the change. Around this time, the Drahvin leader's name was changed from Gar to Maaga. The Chumbley performers—Angelo Muscat, Jimmy Kaye, and William Shearer—were hired through a company called Lester's Midgets. Filming A week of filming took place at Ealing Studios on 21–25 June 1965, largely focusing on the effects required for the serial, such as the opening of the first episode and conclusion