Cloudbase is the fictional skyborne headquarters of the international security organisation Spectrum, from Gerry Anderson's science-fiction television series "Captain Scarlet and the Mysterons" (1967–68).

While developing the series' premise in 1966, creator Anderson remembered that during the Battle of Britain, the RAF's task of countering the Luftwaffe quickly had been complicated by the delay caused by launching from the ground: "... it took [the Spitfire squadron] about 20 minutes to climb high enough to intercept the bombers that were already at 16,000 feet." Thus, he resolved to make the headquarters of the fictional Spectrum Organisation a hovering, airborne aircraft carrier: "This could launch aircraft that would then climb to 100,000 feet and intercept extraterrestrial invaders within minutes." Complete with flight deck and powered by jet engines, Cloudbase hovers at a fixed altitude of 40,000 feet (7.6 mi; 12 km).

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