Editing Gerry Anderson (section)

===''Thunderbirds''===
{{Main|Thunderbirds (TV series)}}
APF's next project for ATV was inspired by a [[Wunder von Lengede|mining disaster]] that occurred in West Germany in October 1963. This real-life drama inspired Anderson to create a new programme format about a rescue organisation, which eventually became his most famous and popular series, ''[[Thunderbirds (TV series)|Thunderbirds]]'' (1965–1966). The dramatic title was inspired by the letter Anderson's older brother Lionel had written to his family during World War II.

Grade was very enthusiastic about the concept and agreed to back a series of 25-minute episodes (the same length as ''Stingray''), so the Andersons scripted a pilot episode, "[[Trapped in the Sky]]", and began production. Anderson initially wanted actress [[Fenella Fielding]] to perform the voice of [[Lady Penelope Creighton Ward|Lady Penelope]], but Sylvia convinced her husband that she herself ought to play the role. ''Thunderbirds'' also marked the start of a long professional association with actor [[Shane Rimmer]], who voiced [[Scott Tracy]].

Production on ''Thunderbirds'' had been under way for several months when Grade saw the completed 25-minute version of "Trapped in the Sky". He was so excited by the result that he insisted that the episodes be extended to fifty minutes. With a substantial increase in budget, the production was restructured to expand episodes already filmed or in pre-production, and create new 50-minute scripts for the remainder. Grade and others were so convinced that ''Thunderbirds'' would be a success that a feature-film version of the series was proposed even before the pilot episode went to air. At this approximate time, APF was renamed Century 21 Productions.

After APF was renamed Century 21 Productions, it enjoyed its greatest success with ''Thunderbirds'', and the series made the Andersons world famous. However, it was cancelled midway through the second series because Grade was unable to sell the show to an American network. Despite being wildly popular in the UK and abroad, Grade felt that without an American buyer, a full second series would fail to recoup its cost. It would later find moderate success in the United States through [[Broadcast syndication|syndication]].

During the production of ''Thunderbirds'' the Andersons' marriage began to come under increasing strain, and the company also had a setback when the feature film ''[[Thunderbirds Are GO]]'' surprisingly {{Citation needed|date=April 2024|reason=Why was it surprising? Who was surprised?}} flopped. In later interviews, Anderson said that he considered divorce, but this was halted when Sylvia announced that she was pregnant. Their son, Gerry Anderson Jr., was born in July 1967.

By that time, production had started on a new series, ''[[Captain Scarlet and the Mysterons]]'' (1967), which saw the advent of more realistic marionette characters which, thanks to improvements in electronics which allowed miniaturisation of the lip-sync mechanisms, could now be built closer to normal human proportions.

Century 21's second feature film, ''[[Thunderbird 6]]'', was also unsuccessful, and the problems were compounded by their next (and penultimate) Supermarionation series, ''[[Joe 90]]'' (1968). This series returned to more 'kid-friendly' territory, depicting the adventures of a young boy who is also a secret agent and whose scientist father uses a supercomputer called 'BIG RAT' which can 'program' Joe with special knowledge and abilities for his missions. Its relatively poor reception made it the last of the classic Anderson marionette shows.