Behind the scenes, it was notable for its then-groundbreaking use of out-of-sequence recording. The final episode, "The Bomb", was the first in Doctor Who history to be recorded according to set availability and then edited into proper sequence. (DCOM: "The Bomb") Director Michael Imison also notably achieved a number of special effects shots through the liberal use of forced perspective, something which hadn't been widely attempted in Doctor Who to that time. Imison's use of playback to indicate that the bridge computers and control consoles on the Ark were fully operational was also unusually sophisticated for the Hartnell era.