"Cockleshell Heroes" is also the name of a military march tune and is frequently heard being played by the Band of the British HM Royal Marines.
Bryan Forbes's script was rewritten by Richard Maibaum at the request of José Ferrer. Irving Allen then had Forbes rewrite Maibaum's revision and direct some sequences. This was done as Maibaum's version was not humorous enough and without Ferrer's knowledge. Ferrer then found out about this other re-write and then walked way from the movie.
David Lodge who plays Marine Ruddock thought that of his 100-plus films this was the best.
Vivienne Knight in her Trevor Howard biography 'Trevor Howard: A Gentleman and a Player' states in relation to this movie that " . . . the Portuguese government had decreed that filming in Portugal for this movie would have to stop unless the film company guaranteed to make a documentary about Portugal to be shown with 'Cockleshell Heroes'. It was a rare stab at blackmail coming from any government, particularly as it must have been obvious that, once the film was sold for distribution, nobody could possibly guarantee that another film would be shown with it. However, Euan Lloyd Warwick Pictures production assistant was not about to argue. He had been deputized to write, produce and direct the documentary; he also got the excellent second unit cameraman, Ted Moore, who later won an Oscar for A Man for All Seasons. Trevor Howard volunteered to do the commentary. The schedule was arranged to give Trevor two free days and the unit of three went off to shoot footage of caves and any other points of interest they could find. They also found the famous fado singer,
A film review in the 'Hollywood Reporter' states that German patrol boat crews and sentries in this movie were played by professionally trained British marines and sailors.
According to 'Daily Variety', during April and May of 1955, there was four weeks of location filming for this movie in Portugal, situated in the environs of the Tagus River.
According to an article in 'The New York Times', production company Warwick Films considered shooting this movie in the CinemaScope format. If this had been the case, this would have been the first English film to do so.
According to the 'Hollywood Reporter' in September 1956, this movie was the first non-German war film to be screened in West Germany.
American movie debut for British actor Trevor Howard.
British actor Trevor Howard once said of this movie: "The best thing about 'Cockleshell Heroes' was filming in Portugal. Beautiful country. While I was there I ended up doing the commentary for a documentary about the country which won more awards than the film ever did. I went all over the world promoting the documentary. As for the film - well."
First feature of Jess Conrad.
First film from the British Warwick production company that was filmed in Cinemascope.
Of all of Victor Maddern film roles this was his favorite role.
Only two of the canoe commando marine characters survive this movie's military mission. They are Major Stringer (José Ferrer) and Marine Clarke (Anthony Newley). This is in keeping with the same number of survivors in the actual Second World War Operation Frankton that this movie is based on. The rest of the marines were either captured, interrogated and executed or drowned. The two real life survivors were Ex-Corporal Bill Sparks (W.E. Sparks and Major H. G. Blondie Hasler aka R.M. {Retd} Colonel H.G. Hasler D.S.O., O.B.E (H.G. Hasler) and they both acted as technical consultants and advisers to this movie.
Scenes at the marine training boot camp were filmed at the Eastney Barracks, Southsea, Hampshire, England. This facility is now the British Royal Marines Museum.
Second film directed by José Ferrer.
The 'Hollywood Reporter' in January 1953 reported that Hugh Hastings had been commissioned to write the film script for this movie but he is not listed as one of this movie's writers in its credits and as such it is not known to what extent his work (if any) was included in the final shooting script.
The 'Los Angeles Times' in April 1956 reported that this movie's United States Premiere in San Diego, California was attended by members of the USMC - the United States Marine Corps.
The Cockleshell of the title refers to the small two-man Cockle MK II folding kayak canoes that were used in the mission attack on the Nazi shipping at Bordeaux.
The depth-charge bombing German anti-submarine ship in this movie was played by two ships from the Royal Navy, the HMS Leeds Castle and the HMS Flint Castle.