played by a Spectrum officer codenamed Captain Sienna. This character was replaced with Magenta to avoid the cost of making a new sienna-coloured Spectrum uniform. Filming began on 25 October 1967, less than three weeks before Joe 90, Century 21's next series, entered production. To avoid overworking the designers, who were busy preparing for the new series, the episode was devised as a bottle show to reduce the number of puppets and sets required: unique among Captain Scarlet episodes, it features no characters other than the regular cast and was filmed mostly on existing sets. The previously unseen Cloudbase Radar Room was created using walls and props that were originally built for Thunderbirds Are Go (1966) and earlier Captain Scarlet episodes. "Attack on Cloudbase" is also one of only two episodes (the other being "Flight to Atlantica") to feature all of the regular cast, though not all of them have speaking parts. The scenes of Symphony Angel in the desert and the Mysterons attacking Cloudbase presented a number of challenges for Century 21's special effects department, headed by Derek Meddings. A scene in which Symphony looks up as Destiny Angel's fighter flies past her required close collaboration between the puppet operators and the effects crew, the former keeping the puppet under control while the latter moved the scale model across the set. The Mysteron spacecraft were modelled on "flying saucer" UFOs commonly reported during the 1960s. To make the spacecraft appear to spin in the moonlight, Meddings added "veins" to each model to reflect the lighting in the studio. Due to a shortage of model operators on set, the models were flown only in the foreground; flashing light bulbs were fitted to the backdrop to give the impression of a larger fleet. Actress Liz Morgan, who voiced Destiny and Rhapsody Angels, was overcome with emotion at one point during the dialogue-recording session: "It was a moment when Destiny was very worried about Captain Scarlet and she was making impassioned pleas for him. Well, I started to cry, and immediately a voice came down from the recording booth and [producer] Reg Hill, who was directing that particular week, said, 'No, Liz, love. Do it again, love. Puppets don't cry!'" Just before Cloudbase hits the ground, Colonel White is shown standing to attention and saluting in a spiralling freeze-frame shot. Anderson based this on maritime tradition, stating that he wanted the audience