The UFOs depicted in UFO: The Series are a number of alien starships and spacecraft that are engaged in brutal attacks upon the people of the planet Earth, from whose corpses they are harvesting human organs for their own survival. They were first seen in "Identified," the very first episode of the series.
The physical appearance of the UFOsEdit
A typical UFO (pronounced "YOU-foh" in the series) resembles an inverted top with large round metal plates ringing its base. These plates radiate out from a central hub that spins clockwise, when viewed from the top, in flight. The outer shell of the craft is transparent, but surrounds an opaque core.
The materials of which a UFO is constructed tend to age rapidly in Earth's atmosphere. Hence, S.H.A.D.O.'s commander, Edward Straker, has given standing instructions that though UFOs are to be shot down and destroyed whenever necessary, at least one is to be brought intact to S.H.A.D.O. headquarters if at all possible. So far, this has not been possible.
Arsenal and flight dynamicsEdit
What makes the UFOs dangerous is that they are armed with a directed-energy weapon of unknown type, presumably some sort of high-powered laser, which can incinerate several hundred cubic feet of matter from distances whose limits have not been determined, but which can presumably reach over one statute mile in distance. In "Sub Smash," a UFO used this weapon to disable the SkyDiver submarine.
The location of the planet whose people are actually launching the UFOs to Earth for purposes of survival remains a mystery. However, its distance from Earth is presumably great enough for UFOs to be able to exceed the speed of light in order to reach Earth from there.
The main limitation on UFOs is that as they approach Earth, they have to slow down in order to enter Earth's atmosphere, which renders them vulnerable to counterattack from the three MoonBase Interceptors. Once actually in Earth's atmosphere, they become even more vulnerable to counterattack from the Sky One aerial interceptors and/or the ground-based Mobiles, since Earth's atmosphere, as previously stated, causes the materials of which they consist to age rapidly upon exposure to it.
A UFO's typical operator, humanoid in appearance, is a representative of the dying alien race that is attacking Earth to harvest human organs for survival. Since the journey to Earth is obviously a long and difficult one even at multiples of "SOL," the speed of light, the aliens, who wear orange life-support suits with silver helmets, use an oxygenated liquid for breathing during flight. This liquid is green in color, and it imparts an artificial greenish tinge to the skin with prolonged use.
The oxygenated liquid the aliens breathe in flight apparently also slows their aging to a degree. For upon exposure to the air of Earth's atmosphere, an alien accustomed to breathing the liquid commences to age a matter of years in a matter of hours. They are not averse to using it for the purpose of torture of terrestrial humans, as their use of it upon Paul Foster for just that purpose in "Ordeal" demonstrates.
The fact that the aliens are harvesting human organs for survival became clear in "Identified," when the first alien S.H.A.D.O ever successfully captured died and was autopsied. The donor of his heart proved to be Leila Carlin, the sister of Lieutenant Peter Carlin of S.H.A.D.O., who had been killed in an alien attack in 1969.
The origin of the UFOs and their occupants is thought to be the star system Alpha Centauri, 4.3 light years from Earth, but this is never confirmed. It is revealed in "Close Up" that it takes the UFOs 4 months to travel to Earth from their star system of origin.