Thunderbird 2 is attacked and crash-landed on Tracy Island. For this scene, a large model of the famous craft was destroyed during filming. The special effects team carefully chose one particular model for this purpose that was not perfect in detail.
This is the first episode in which Thunderbird 4 is used. It is also the only time she is not airlifted by Thunderbird 2.
This episode is the first of two showing a Thunderbird being shot down. The second is "The Uninvited" in which Thunderbird 1 is shot down by a Zombite fighter plane.
This is the first of two episodes in which Virgil Tracy's vehicle, Thunderbird 2, was not involved in the story's primary rescue. This is because the episodes were originally made as a half-hour show; when Sir Lew Grade of ITC demanded the series be remade in one-hour format, AP Films had writer Alan Fennell write in the subplot where Thunderbird Two is mistaken for an enemy bomber and attacked by a US warship; ironically, this helped make this episode one of the most fondly remembered by original fans of the show. It also explains why this episode needed two directors (David Elliott and David Lane).
'Fulmer' is a village near Slough, not far from the AP Studios where Thunderbirds was filmed - so presumably the 'Fulmer Finance' building's name was probably inspired by this.