Arthur Provis, Reg Hill, and John Read. Pitched in late 1963, the series was commissioned by Lew Grade of ITC, APF's parent company, on the back of the positive audience response to Stingray. Gerry Anderson drew inspiration for the series' underlying concept from the West German mining disaster known as the Wunder von Lengede ("Miracle of Lengede"). In October 1963, the collapse of a nearby dam flooded an iron mine in the municipality of Lengede, killing 29 miners and trapping 21 others underground. Lacking the means to drill an escape shaft, the authorities were forced to requisition a heavy-duty bore from Bremen; despite the considerable time necessary to transport the bore by rail significantly reducing the chances of a successful rescue, 11 of the trapped miners were eventually saved. Recognising the advantages of swifter crisis response, Anderson conceived the idea of an "international rescue" organisation that could use supersonic aircraft to transport specialised rescue equipment quickly over long distances. Seeking to distinguish his proposal from APF's earlier productions, Anderson attempted to pitch the stories at a level that would appeal to both adults and children. Whereas previous series had been broadcast in late-afternoon children's timeslots, Anderson wanted Thunderbirds to be shown during the evening to attract a broader family audience. Sylvia remembers that "our market had grown and a 'kidult' show ... was the next step." The Andersons retired to their holiday villa in Portugal to expand the premise, script the pilot episode and compose a writers' guide. According to Sylvia, the writing process depended on a "division of labour", whereby Gerry created the action sequences while she managed characterisation. The decision to make a father and his sons the main characters was influenced by the premise of Bonanza, as well as Sylvia's belief that the use of more than one heroic character would broaden the series' appeal. The Tracy brothers were named after Mercury Seven astronauts: Scott Carpenter, John Glenn, Virgil "Gus" Grissom, Gordon Cooper and Alan Shepard. The series' title was derived from a letter written by Gerry's brother, Lionel, while he had been serving overseas as an RAF flight sergeant during World War II. While stationed in Arizona, Lionel had made reference to Thunderbird Field, a nearby United States Army Air Forces base. Drawn to the "punchiness" of "Thunderbirds", Anderson renamed the series, whose working title had been "International Rescue", as well as the star vehicles, which