A model of a submarine was created by purchasing a Woolworth's submarine model kit and then altering the propeller. By chance, the alterations to the model strongly resembled an actual prototype submarine being developed by the Ministry of Defence. After footage of the model was broadcast as part of the story, Barry Letts received a visit from two Ministry of Defence officials, who were concerned that the footage was of the prototype.
Donald Sumpter is one of the 39 actors to have been in both the 20th Century and 21th Century Doctor Who Series.
This episode was watched by 8.3 million viewers on its original transmission.
Donald Sumpter has acted in both the color and black and white era of Doctor who.