Guest star Jill Ireland was in real-life the wife of series star David McCallum. The character she plays in this episode, Marion, was conceived as a recurring character, but the idea was dropped, although Ireland would return to the series several more times, playing Marion and other characters.
The Fear-Makers (1964) (broadcast 9/28/64) also featured a gas that induced fear in those exposed to it - so within 8 days U.S. television audiences could've seen 2 different shows with this very similar plot device.
Armand Ravel killed himself rather than face trial for his actions in the French Secret Army. From 1954 to 1962 the North African nation of Algeria fought a guerrilla war for independence from French colonial rule. The right wing French paramilitary Organisation Armee Secrete was a terrorist group that committed many war crimes against Algerians.
The anti-aircraft missile that Pattner and his cronies fire is a radar-directed Raytheon Hawk, considered quite a formidable system. Some of its associated acquisition and targeting radars are also seen. Introduced in the 1960s, Hawk was a mainstay of air defense for the US and its allies through the 1980s.