'Invasion Earth' by Dennis Spooner

A strange cloud is heading for Earth, causing a breakdown of interstellar communication as it approaches. Fireball XL18 is sent to disperse the cloud, but the ship is destroyed; Fireball XL24 is then despatched to investigate, but it too explodes. Having finished an errand of mercy, the crew of Fireball XL5 returns to Earth and discovers that the cloud hides an alien invasion fleet poised to take over the world…

Paul Maxwell (Colonel Steve Zodiac / XL18 Pilot / XL24 Pilot), Sylvia Anderson (Doctor Venus / Eleanor Zero / Jonathan Zero), David Graham (Professor Matt Matic / Lieutenant 90 / Zoony the Lazoon / Colonel Hudson / Alien Leader / Alien Lieutenant), John Bluthal (Commander Zero), Gerry Anderson (Robert the Robot)

Directed by Alan Pattillo
Produced by Gerry Anderson
Associate Producer Reg Hill

TX (UK - ITV):
21st October 1963

Notes:
*Featuring Colonel Steve Zodiac, Venus, Professor Matt Matic, Commander Zero, Lieutenant 90 and Robert the Robot