Mission To The Unknown - Production

Production

The episode came about because the earlier story Planet of Giants was cut from four episodes to three during post production and an additional episode was allocated to the series. Although the cast contracts had not yet been signed, it was difficult to add a single episode to a planned run of four and six episode stories and so it was decided to make a one-off trailer for the forthcoming epic story The Daleks' Master Plan (Serial V).

Terry Nation wrote this episode partially as an attempt to create a story about the Daleks that did not involve the Doctor or his companions, such that he could eventually develop and sell the idea of a Dalek series, divorced from the Doctor Who universe. In the proposed series, the Space Security Service was tasked with hunting Daleks, and it would follow their adventures — an approach that can be seen in short stories and comic strips written for the 1965 Dalek Outer Space Book (cover dated 1966). An unmade pilot titled The Destroyers was written, but the series concept was never sold.

The episode was made by the same team as Galaxy 4 (Serial T), with both stories sharing pre-filming and, possibly, the same production code (see below). It was also the final Doctor Who episode on which Verity Lambert served as producer.