20 March 1965: broadcast of "The Centre", sixth episode of the story we now call The Web Planet. The Doctor and Vicki are captured by the Animus; but Ian and the Optera attack from below, and Barbara and the Menoptera from above, and Barbara destroys it.
20 March 1971: broadcast of second episode of The Claws of Axos. The British are determined to control the world's supply of Axonite; the Axons, however, are a parasitic organism intending to suck the planet of all its energy.