The S.H.A.D.O. maintains a MoonBase as one of its first lines of defence against UFOs. This MoonBase is located in the Sea of Tranquillity and is in constant communication with the S.I.D., or Space Intruder Detector, and three interceptors are maintained there in a state of almost-constant standby.
Female MoonBase personnel wear purple wigs as part of their uniforms. Though various explanations for this have been advanced, these were actually part of Sylvia Anderson's "Century 21 Fashions" designs for the cast, and they serve no functional purpose.