Throughout this serial, we’ve seen a large, full-scale space capsule for the actors to climb in. I was interested to learn that this prop was built in a shared-cost budget with another BBC drama, Doomwatch. This allegedly “sci-fact” show about civil servants saving the world from dangerous new technologies and ecological disasters was created by a pair of former Doctor Who‘s regular writers, Kit Pedler and Gerry Davis. It debuted the week after “Doctor Who and the Silurians” began, and the capsule was used in episode six, “Re-Entry Forbidden,” which was shown five days before the first episode of this serial. I wonder whether anybody watched both shows in March 1970 and noticed.
After watching part four, I showed our son a picture of John Levene’s character of Corporal Benton from “The Invasion” to refresh his memory, because Benton, now a sergeant, resurfaces in this episode. There’s a neat story about how this character got promoted to semi-regular. He was one of many good guy military characters in “The Invasion,” which Douglas Camfield had directed. Camfield was in line to direct the next serial, “Inferno,” and since there was room in the script for a Sergeant Anybody character, he asked whether they could rehire John Levene, as he enjoyed working with the actor. The production team reasoned that there was also a Sergeant Anybody in this story, and so it might make a little sense to start using some familiar faces in UNIT rather than a revolving bunch of guys in beige uniforms. That worked out quite nicely. Everybody likes Sergeant Benton.