Credited as technical advisor for war games models, respected figure designer Peter Gilder supplied Schneider's American Civil War diorama, built by himself. In 1978 he was reunited with Woodward as a combatant in editions of Battleground (1978), a six-part war gaming series made by Tyne Tees Television which it is thought reused some of the figures and terrain from this film (certainly the Battle of Gettysburg featured in one edition).
In the original teleplay, Callan decides to kill Schneider with a Noguchi Magnum after discovering that Schneider is running guns for the corporation. In the film, this reference has been deleted. However, there is a scene in which Hunter surprises Callan as he visits the library to research the Noguchi Corporation. Without the Schneider/Noguchi connection, there seems no reason for Callan to be interested in where the gun came from, and it seems possible that this scene is a leftover from an earlier script draft that preserved the original plot twist.
Anthony Valentine was unable to reprise his television role of Toby Meres, as he was busy recording the BBC's WWII drama Colditz (1972).
First film with optical soundtrack (mono) encoded with A-type Dolby noise reduction.