Thunderbirds was a British science fiction television series created by Gerry and Sylvia Anderson, filmed by their production company AP Films (APF) and distributed by ITC Entertainment. It was filmed between 1964 and 1966 using a form of electronic marionette puppetry called "Supermarionation" combined with scale model special effects sequences. Two series, totalling 32 fifty-minute episodes, were made; production ended with the sixth episode of the second series. The main characters are the leader of International Rescue, ex-astronaut Jeff Tracy, and his five adult sons, who pilot the Thunderbirds. Thunderbirds premiered in September 1965 on the ITV network and has since aired in at least 66 countries. Widely regarded as the Andersons' most popular and commercially successful series, Thunderbirds has been praised for its special effects, directed by Derek Meddings, and its musical score by Barry Gray. It is also remembered for its title sequence, which begins with an oft-quoted countdown by Jeff Tracy voice actor Peter Dyneley: "5, 4, 3, 2, 1 – Thunderbirds Are Go!" Each puppet had more than 30 individual components, the most important being the solenoid – located inside the puppet's head – that synchronised the movements of the flexible lower lip with the syllables in the character's pre-recorded dialogue. The head had to be large enough to accommodate the solenoid, causing the torso and limbs to look disproportionately small. Guild members Christine Glanville, Mary Turner, John Blundall and Judith Shutt, all worked on the series.