- Creator's Favorite Episode: Director Richard Martin considered this to be the best of the first three Dalek serials.
- Enforced Method Acting: Carole Ann Ford cried real tears filming Susan's departure.
- Hostility on the Set: Ann Davies (Jenny) recalled finding William Hartnell intimidating and thus kept her distance from him.
- Name's the Same: This serial's Jenny is not the Doctor's daughter, or a Silurian's assistant/lover, or the mother of the Family of Blood.
- Prop Recycling: The four original Dalek casings constructed for "The Daleks" were used again in this serial. Two of these had to be borrowed back from Barnardo's children's home in Stepney, to which they had been donated following the broadcast of the original serial. Two new Daleks were also constructed.
- Recycled Set: Multiple Dalek sets from Dr. Who and the Daleks were reused. Due to dates, the serial actually aired before the film came out, making this the sets' first appearance.
- Wag the Director:
- What Could Have Been: Wells was originally only to have appeared in episode three, but according to Nicholas Smith on a documentary accompanying the serial's DVD release, he talked the director into letting him lead the miners' revolution in episodes five and six.
- The original script featured a teenaged rebel named Saida, an English girl of Indian descent who was revealed as Dortmun's daughter after his death. Saida stowed away aboard the TARDIS at the story's conclusion, becoming the new companion. Subsequently, this character evolved into Jenny, who was also considered to become a companion.
- The Robomen were conceived as wearing only a small disc on their temple, with wires snaking into the hair.
- Instead of crocodiles, David and Susan were menaced by mutated humans in the sewers.
- Wells' role was originally much smaller he was freed from the Dalek shuttle by Ian and left to tend to other escapees.
- Originally, three old women lived in the shanty in the woods, rather than the degenerate mother and daughter.
- The original climax saw the Daleks attempt to kill all their slaves by trapping them in the mines, which would be deluged with lava when the bombs exploded.
- Working Title: The Daleks, The Invaders, The Return of the Daleks and The Daleks in Europe. Working titles for the fourth and sixth episodes were "The Abyss" and "Earth Rebels" respectively.
- Written-In Infirmity: William Hartnell injured his back while filming the scene where the Doctor is carried up a ramp. The actors playing the Robomen and the Dalek prisoners had been instructed to break step while traversing the ramp but had failed to do so. This weakened the integrity of the structure, causing it to collapse. Although Hartnell was well enough to continue with the day's shooting, he was still experiencing pain days later. After correspondence from Hartnell's lawyer, the BBC agreed to pay for an x-ray, which fortunately indicated no permanent trauma to the spine. As a result, the Doctor is out of Episode Four. This caused a rewrite originally, it was he who noticed the Dalek firebomb; in the recorded version, it was David who made the discovery. The Doctor instead collapsed at the very start of the scene, and the dialogue written for him was shared between David and Susan.
Trivia / Doctor Who S2 E2 "The Dalek Invasion of Earth"