Thunderbird 6 is a 1968 British science-fiction adventure film written by Gerry and Sylvia Anderson, directed by David Lane and produced by Century 21 Cinema. A sequel to 1966's Thunderbirds Are Go, it was the second film to be adapted from the 1960s television series Thunderbirds, which combined scale models and special effects with marionette puppet characters in a filming process that the Andersons termed "Supermarionation". Intended to provide a lighter-hearted cinematic experience to contrast with the harder science of Thunderbirds Are Go, the Andersons elected to base the plot of Thunderbird 6 on Skyship One, a futuristic airship that is the latest project of the scientist Brains.
The film's plot depicts Alan, Tin-Tin, Lady Penelope and Parker representing International Rescue on Skyship One's round-the-world maiden flight, unaware that criminal mastermind the Hood is once again plotting to acquire the secrets of the Thunderbird machines. Paid agents of the Hood murder the original crew of Skyship One prior to take-off and assume their identities, entertaining the guests while scheming to lure the Tracy brothers into a trap. Meanwhile, Brains' efforts to produce a satisfactory design concept for Jeff's proposed Thunderbird 6 collide with fate when Skyship One is damaged and Alan's old Tiger Moth biplane appears to be the only hope of saving the International Rescue group and their impostor hosts.
Actors John Carson and Geoffrey Keen provide guest speaking roles, with additions to the regular voice cast in the form of Keith Alexander and Gary Files. The design of the puppets that appear in Thunderbird 6 marks a transition between the caricatures that Century 21 had used up to Thunderbirds Are Go and the realism introduced in Captain Scarlet and the Mysterons. Filming ran from May to December 1967, and the art and special effects departments collaborated to realise Skyship One as both a miniature model and a collection of themed interior designs. A number of sequences of the Tiger Moth in flight were filmed on location with a full-sized stunt plane, but a legal dispute with the Ministry of Transport regarding alleged dangerous flying by pilot Joan Hughes forced the production team to film the remaining shots in-studio with scale replicas.
Released in July 1968, Thunderbird 6 had a mediocre reception at the box office, which ruled out the production of further sequels in the Thunderbirds film series. Critical response has remained mixed: although the special effects have been praised, commentators are divided on the quality of the plotting, which is considered either well-paced and concluding on a note of high action, or confusing and inordinately long, with little visual spectacle to contrast with the dialogue. Nevertheless, Thunderbird 6 is viewed favourably in comparison to Jonathan Frakes' 2004 film adaptation, receiving praise for the perceived agelessness of its entertainment value.
