Supermarionation a puppet hand, suspended by wires, operating the controls of "Thunderbird 1". The term "Supermarionation" was not coined until during production of later episodes of "Supercar". As a result, "Four Feather Falls" is often omitted from lists of Supermarionation productions. Two feature films based upon "Thunderbirds" were also made with Supermarionation: "Thunderbirds Are Go" (1966) and "Thunderbird 6" (1968). Numerous episodes of "Thunderbirds", "Captain Scarlet", and other series were also edited together (sometimes with the addition of new narration) to form movie-length features for VHS release and TV syndication in the 1980s. "The Secret Service" was actually a hybrid of
Tex and the Lord of the Deep most popular and long-lived comic strip characters. Attempts to adapt the "Tex" comic series to film appeared as early as the late 1960s. These included Sergio Bonelli working on an adaptation with Charlton Heston (as Tex) and Jack Palance (as Kit) being considered for the roles. Beonlli approached Tonino Valerii and Enzo G. Castellari to approach the character. Valerii recalled being approached by Gian Luigi Bonelli in the early 1970s. Valerii liked the idea but found that Bonelli wanted to make a film where he would personally handle the costumes and changed the original story which never got into production.