UFO followed the adventures of the secret organization called S.H.A.D.O. (ten quatloos if you can recall what that acronym stands for) as it monitored and defended earth from alien attackers.
UFO featured nifty future fashions, and tons of cool miniature effects courtesy of the late, great Derek Meddings and modelmaker extraordinare Martin Bower. There was the Moonbase and their Interceptor spacecraft (they look a bit like early versions of BSG's Viper fighters), the orbiting S.I.D. (Space Intruder Detector), the mighty Mobiles and lest we forget, the incredible SkyDiver submarine with detachable Sky 1 fighter.
Oh, this shit rocked.
UFO also had one of the snazziest theme songs out there, composed by Barry Gray. So put on your go-go boots (and purple wigs) and lets go hunt aliens. I'll fire up the Interceptors.