The Invasion is the first story to feature the United Nations Intelligence Taskforce. It was designed by its writer, script editor Derrick Sherwin, to be a sequel to The Web of Fear - as well as acting as a trial run for a planned change to the format of the series, where the Doctor would be based on Earth full time, and involved in some Quatermass-style adventures.
Initially it had been hoped to have Colonel Lethbridge-Stewart, Professor Travers and his daughter Anne all making a return. This would have cost a little as the characters were created by writers Henry Lincoln and Mervyn Haisman (with whom Sherwin had just fallen out over The Dominators).
In the end only the Colonel came back - now promoted to Brigadier and placed in charge of the military-scientific UNIT, which would form the backdrop to the planned changes.
The Invasion adds to that decades long UNIT dating controversy, which got underway in The Web of Fear. The Abominable Snowmen had been said to take place in 1935, but Travers talked about it taking place 40 years before meeting the Doctor, Jamie and Victoria again in the London Underground - placing Web around 1975.
Here, the Brigadier states that the events of Web were around four years ago. That would push this Cyberman story to 1979.
The production team certainly intended the UNIT stories to be set in the near future, but the problem is that they never gave any definitive dates on screen. This near future setting was also hampered by the presence of things which contradicted it - such as the lack of any Victoria Line in Web, meaning it has to be set around the time of broadcast, rather than the mid 1970's.
This story includes a scene where Zoe destroys an International Electromatics computer with an insoluble problem using ALGOL. It's unlikely someone from the 21st Century would be familiar with ALGOL (it dated rapidly). Computers don't blow up when given problems they can't solve. An error message perhaps, or it would have just sat there. Wendy Padbury struggles with the word "integer" in this scene.
Season Six suffered, more than any other, from problems with scripts. I strongly suspect that this was down to the personality of Sherwin himself, as no other script editor suffered quite the problems he had to contend with regarding last minute story collapses.
The Invasion was supposed to be a shorter story, but got extended to 8 episodes due to issues with other scripts. The Cybermen don't turn up until the halfway mark, but at least we have an excellent human villain to keep us interested until they get here. This is Tobias Vaughn.
There's a scene where Vaughn bullies Prof Watkins. The old scientist says he will shoot Vaughn if gets half a chance - so Vaughn gives him a gun. He's confident in his survival because he's been given a Cyberman body - but what if Watkins had shot him between the eyes? He's only Cyberman from the neck down.
How many Cybermen are there in London? We're told of many UFO sightings before the story even starts, and see lots of pods at the IE premises - yet Vaughn and his goons are reanimating them one at a time.
Vaughn has also left his duplication of the Cerebration Mentor a bit late - having only a single example just before the invasion is due to commence. He seriously thinks this will allow him to dominate the Cybermen globally.
The scenic crew have trouble with the panel which opens and closes to reveal the Cyber-Director - and at times you can clearly see the wires which are working the machine.
The word "Cybermen" doesn't get used in the story title, or in any of the dialogue until they have appeared on screen. Fine, but the Radio Times printed a picture of one to accompany the first episode.
The Cybermen have remarkable defences at their base on the Moon, to accurately target a missile at the TARDIS in space when it has only just materialised.
(And where is the Master from The Mind Robber? This story begins with the TARDIS coming back together again, so it must prove that the events of The Mind Robber were all in the Doctor's head).
Later, the Cybermen can't hit the Earth with a missile without coming very close in - and their fleet can't find the planet without a homing beacon, despite having a base on the Moon. And what happened to that base? It just gets forgotten about.
Zoe mentions them seeing a spaceship on the moon, when they didn't.
What is the Cyberman plan, as it seems to change as the story progresses. They want to invade the Earth, but only attack London. After a setback, they then decide to drop a bomb. Why not just drop the bomb in the first place? It sounds that they are more interested in exploiting the planet's mineral wealth, rather than capturing humans for conversion.
Why do the Cybermen insist on going along with Vaughn and, more importantly, why does Vaughn put up with Packer?
Watkins' rescue takes place off screen - we're just told about a great action sequence. (We know this was because director Douglas Camfield ran out of time on location filming, but it still looks bad on screen). It's immediately followed by Gregory's death, which is so rushed that - pre-VHS age - some people thought it wasn't even Ian Fairbairn who was being gunned down.
There is an overdose of stock footage in the final episode, and the model work is terrible, as we see fireworks bouncing off the models - failing to match the description of what the missiles are supposed to be doing.
This is the penultimate story which is incomplete - episodes one and four being missing. However, Nicholas Courtney was on record for claiming to have seen a tape of these, albeit silent copies.
