This mini-series was filmed as that and then re-cut into a two hour theatrical release version, and as such, exists as a six hour mini-series and a two hour feature film.
Evan Michaelian (Michael York) is the only completely fictional character.
Art Director Keith Wilson once said of his quest to find an original Enigma coding machine for the production: "The secrecy surrounding Enigma is one of the most fascinating achievements of World War II. For over thirty years, no one in the know said or wrote anything at all about the acquisition of the German code machine. All of which, of course, made my job more difficult. My search for Enigma wasn't as crucial as (William) Stephenson's, but as filming got under way, and the Enigma machine seemed as untraceable as ever, it began to take on something of the same urgency. Finally, I visited an old mate of mine who hires out props to film companies, and for the hundredth time I asked the same question: 'Don't suppose you have an Engima machine?' The usual response was total puzzlement, but he replied quite calmly: 'No, but I know where you can get one.' And he did, too."
The meaning and relevance of the word "Intrepid" from this mini-series' title was that it was the code-name for Sir William Stephenson, who ran a top secret spy ring organization during World War II. This mini-series is about events relating to this spy network.
Sir William Stephenson was pleased that David Niven was cast to play him in this mini-series. Niven was actually one of the wartime secret agents in the "Intrepid" spy-ring organization. Stephenson once said of Niven: "He's one person who knows what real war means. (Sir Winston) Churchill told me personally that, although David had left Britain by then and gone to Hollywood to be in movies, 'David is a fine young man'. Despite the fact that he was doing a job in Hollywood, Niven came back to England to serve in the war, and I regarded him highly for that."