The color master tape of this episode was wiped by the BBC in the 1970s and the BBC only held a 16mm black and white telerecording. The episode remained only in black in white until the 1990s, when the color signal from a domestic NTSC recording and the black and white telerecording were used to create a new color master on D3 digital tape.
The side arms used by the UNIT officers should have been Brownings. The long single barrel shows they were not.
This episode was watched by 7.5 million viewers on its original transmission.