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 several German battleships, namely the "Lutzow", "Scharnhorst", and "Tirpitz", in northern Norway, using X-class mini submarines.
James Caan received top billing. Caan plays a Canadian amongst a cast of characters who are predominantly English.
This World War II submarine movie was based on an actual mission, while the Australian videocassette sleeve notes state that this movie is, "Based on classified data released by the British Government."
The movie utilizes black and white archive footage (such as for parachuting) as part of the story (not as historical reference) and as such, these shots do not match.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 and black and white intercutting to occur in a full color movie, where the archive footage is not intended to be a historical reference.