Director Kevin Connor said "Doug McClure was a great asset. In fight scenes he was especially good due to his hours of American TV action films. He knew exactly where the camera was at all times and threw punches precisely where the effect would work for the screen. He was always co-operative and came up with many ideas."
The real U-33 of World War One served in the Mediterranean and survived the war.
Michael Palin found a gun from this production in a skip in the studio where this was shot. He kept it.
The film was the 14th biggest hit at the British box office in 1975.
Special effect technician Roger Dicken confirmed that the film's dinosaurs take inspiration from the paintings of famous mid-20th century Czech artist Zdenek Burian, one of the most prolific paleoartists of all time. The Styracosaurus was based directly on Burian's painting and therefor has the same anatomical inaccuracies, such as an overly wide snout. Burian's painting was actually a copy itself, he had based it on the dinosaur models of American sculptor Vernon Edwards.