In a 2014 interview with "Doctor Who Magazine", script editor Terrance Dicks recalled that he was present at the "birth" of UNIT during the production of the "Doctor Who" serial "The Invasion" (1968). He credited both scriptwriter and script editor Derrick Sherwin and producer Peter Bryant as having come up with the idea beforehand, claiming that they were testing the concept in "The Invasion" before it had become central to the show in the "Doctor Who" serial "Spearhead from Space" (1970). In a series of interviews originally recorded for the 2006 DVD of the "Doctor Who" serial "Inferno" (1970), actor Nicholas Courtney, who played Brigadier Lethbridge-Stewart in "The Invasion", similarly described "The Invasion" as a "dummy run" for the idea of the Doctor, the main protagonist of "Doctor Who", being exiled to Earth. Dicks also said that the idea of exiling the Doctor was done because making every serial take place on Earth was cheaper to produce than if every serial had to have a new alien planet built, and that UNIT was an idea Sherwin had come up with to answer the question of what to do with the Doctor after he was exiled to Earth. Speaking in an interview on the 2012 DVD of the "Doctor Who" serial "The Krotons" (1968–69), Sherwin said that he wanted "Doctor Who" to be "down on Earth anyway, for credibility", and described UNIT as "the ideal vehicle" for this.