Most people think that episode 10 of the Dalek's Master Plan (Escape Switch) was deleted. It was, in fact, never filmed. The BBC instead, Showed episode 3 of the chase, hoping that most people would forget most of the story as it was the 10th episode.

The Doctor Who story "Fury From the Deep" was the first to feature the Doctor's favourite gadget, the "Sonic Screwdriver". The "Sonic Screwdriver" has popped up in Doctor Who stories many times since...even as recently as the 1996 TV Movie of Doctor Who (the one that starred Paul McGann as the Doctor). Sadly, it cannot be seen in "Fury from The Deep" as every episode of that story was destroyed by the BBC in 1977.

Only episode one of this six part Doctor Who story survives, but it has been digitally restored by the BBC to 'broadcast quality'. Indeed, it WAS broadcast on the BBC's digital channel BBC4 as recently as June 26, 2004, as part of that channel's Sixties Season.

Location filming of "The War Games" took place in East Sussex during April 1969. To depict the desolate landscape of "no-man's land" during 1917, the location shoot was done at the Brighton Corporation Refuse Tip at Sheepcote, near Brighton. The very same location had been used just a few months before, also to depict "no-man's land in 1917" by Richard Attenborough, for his film "Oh What A Lovely War"

In one or two of the location filming scenes, Zoe is seen in the background struggling to hold her trousers up. Her belt broke, but filming was so far behind that the director said to carry on.

The episode was intended to prove that Earth-based stories could be produced cheaply and effectively. Ironically, it was the most expensive Doctor Who episode ever produced when made, and remained so for several years.

A stuntman received a bad leg injury in episode 3 when he was hit by the car Jon Pertwee was driving. Jon felt so bad about it that he became ill himself, which threatened to disrupt filming. (Source: DVD commentary).

The actor who plays the man falling off the tower after being shot is actually the same actor as the soldier who fired the shot. (Source: DVD commentary).

Spearhead from Space is the first of only two Doctor Who stories to be originated entirely on film as opposed to videotape; this was an emergency measure necessitated by the unavailability of studios due to industrial action at the BBC. It was also the first ever Doctor Who adventure to be filmed in colour (contrary to popular myth, NO 1960s episodes of Doctor Who were made in colour.

The helicopter that explodes into flames and crashes in this episode was simply a piece of "stock footage" taken from the 1963 James Bond Movie 'From Russia with Love'

This Doctor Who story, first broadcast between April 8th and May 13th 1972, is called 'The Mutants'. However, the second ever Doctor Who story, first broadcast December 21st 1963 to February 1st 1964, was ALSO called 'The Mutants'. Looks as though no-one bothered to check if the title had already been used...

David Troughton, who plays King Peladon, is the son of the second Doctor Who, Patrick Troughton. Both Troughtons had previously appeared together in the Season 6 (1969) story 'The War Games'; Patrick Troughton as The Doctor, and David Troughton in the minor part of a solider called Private Moor. Additional trivia point: David Troughton shared a flat with future (sixth) Doctor Who Colin Baker at the time of the making of 'The Curse of Peladon' (January 1972).

"The Three Doctors" was the last appearance of William Hartnell in (and as) Doctor Who. The show was written to include all three actors that had played the role as a way of celebrating the shows 10th anniversary. However, by the time the show was made, William Hartnell was in failing health (due to the debilitating ailment, arterial sclerosis). Because Hartnell was so frail, he could only play the part of Doctor Who seated in a chair, reading his lines from cue cards. (The plot device of Hartnell being "caught in a time eddy" was written in to explain why Hartnell was only ever seen in the story on TV Monitors). Also due to Hartnell's failing health, his contribution to "The Three Doctors" was limited to one day's filming (Monday 6th November 1972) at the BBC's Ealing Studios. "The Three Doctors" was also the last time Hartnell did any acting: he died two-and-a-half years later, on 24th April 1975, aged 68.

The first thing the Third Doctor does on-screen is collapse out of the TARDIS, which is also the last thing he does in that incarnation.

Chief of Security Nyder wears an iron cross on his uniform which mysteriously disappears in episode 3 - apparently the producers felt it was too close a reference to Nazism so it was removed from the show. (Source: DVD commentary).

The actor Michael Wisher who plays Davros always wore a kilt to the studio, as he preferred it to trousers. It is never seen, of course, as his lower body is always hidden inside his Dalek chair. (Source: DVD commentary).

The filming location for this story was Stargroves, a country mansion near Newbury in Berkshire. At the time, it was owned by Mick Jagger of the Rolling Stones.

A pile of straw - seen in the road as Weng-Chiang searches for the time cabinet - was placed there to hide a modern (1970s) car which had, despite requests to the contrary, been parked in the road prior to filming, and whose owner refused to move it.

Robophobia, an irrational fear of robots, is at one point referred to as 'Grimwade's syndrome'. This was an in-joke reference to production assistant Peter Grimwade (later to become a director and writer on the series) who had bemoaned the fact that the stories on which he was assigned to work almost always involved robots.

The deactivation discs for the robots (or "corpse markers" as they are referred to in the script) are not as glamorous or hi-tech as you might think. They are, in fact, bicycle reflector discs, bought from Halford's Cycle Shops.