James Caan received top first billing. American actor Caan plays a Canadian (a Caanadian?) amongst a cast of characters who are predominantly English.

Apparently, director William A. Graham worked on the film's original screen story with writer John C. Champion but is uncredited for such.

Location shooting was filmed in Scotland.

Operation Source was also the subject of an earlier movie, Above Us the Waves, made about fourteen years earlier.

Released in 1969, this picture was actually produced in 1967.

The fifty-man allie submarine seen at the start of the movie was called the Gauntlet. The name of the German battleship also seen during the opening and later was called the 'Lindendorf'.

The movie utilizes black-and-white archive footage (such as for parachuting) as part of the story (not as historical reference) and as such these shots do not match. It is rare for this type of color - b/w inter-cutting to occur in full color movie where the archive footage is not intended to be a historical reference.

The real life World War II German battleship the 'Tirpitz' was renamed the 'Lindendorf' for this movie.

This film's 'Submarine X-1' title refers to the X class submarine which was a real World War II midget submarine class built for the Royal Navy during the 1943-44 period. The mini-subs were also known as X-Craft.

This movie is based on both the real-life Chariot human torpedo attacks on the German battleship Tirpitz during the Second World War as well as Operation Source, which was a series of attacks by X-class midget submarines on Nazi German warships, the Tirpitz, Scharnhorst and Lutzow, in Northern Norway during World War II.

This war movie is loosely based on a real World War II mission, Operation Source, which was staged during September 1943. Operation Source involved a number of secret attacks on a number of German battleships, namely the 'Lutzow', 'Scharnhorst' and 'Tirpitz', in northern Norway using X-class mini submarines

This World War II submarine movie was based on an actual Second World War mission whilst the Australian video-cassette sleeve notes state that this movie is "Based on classified data released by the British Government."