4 March 1967: broadcast of fourth episode of The Moonbase. The Doctor defeats the Cybermen by using the gravitron to make them float away into space.
4 March 1972: broadcast of second episode of The Sea Devils. The Doctor and Jo escape the the nearby sea base and discover that the Master is stealing equipment.
4 March 1978: broadcast of fifth episode of The Invasion of Time. The Doctor and friends escape, and the Doctor persuades Borusa to let him have the Great Key.