While the ninth episode broadcast, this was actually the twentieth filmed.
The warship uses a Seaslug surface-to-air missile to destroy the UFO in the beginning of the episode. In reality, a Seaslug was only ever fired once at a hostile aircraft, in 1982 during the Falklands War. It missed.
Philip Madoc (Ship's Capt.) is one of the eleven actors to appear in both Journey to the Far Side of the Sun (1969) and the UFO series. This was also his second episode, having previously appeared as Straker's ex-wife's new husband in A Question of Priorities (1970).
At the time of writing this episode's script, Col. Virginia Lake's character was either written as "2nd in Command" or 'Colonel Alec Freeman' ([George Sewell]). By the time of filming, Sewell had left the production of UFO, and it had not been decided who would replace him. Initially, Gary Raymond was considered, but eventually Wanda Ventham was chosen.
Skydiver 1 is known to have had three captains in the course of the series, Peter Carlin (Peter Gordeno), Lew Waterman (Gary Myers), formerly an astronaut pilot of a Moonbase Interceptor, and (David Warbeck).