There was some surprise that Stanley Baker, who in 1960 was considered the most popular British movie star, accepted the relatively small supporting role of Private "Butcher" Brown. Baker revealed that he wanted to be in the movie because he was impressed at how anti-war the screenplay by the blacklisted writer Carl Foreman was.
Gregory Peck often said he was disappointed that so many viewers had missed how anti-war the film was intended to be. Peck was a lifelong pacifist who strongly opposed US involvement in the Korean and Vietnam wars. He was also against joining World War II until Adolf Hitler invaded the Soviet Union.
Actor Michael Trubshawe (Weaver) was David Niven's oldest friend. The two men served in the military together as young men, and Niven was later responsible for persuading Trubshawe to pursue an acting career. Niven also made it an inside joke to try to mention Trubshawe's name in as many of his own films as he could, usually as a reference to some unseen character.
For the scene where the commandos scale the near-vertical cliff, the rockface was a painted backdrop laid out on the ground, so the actors were actually climbing over the studio floor and then the image was tilted in camera.
Although Navarone is a fictional place, the novel of the same title is based on The Battle of Leros, in the Dodecanese, the location of the deepest port in the region and coastal battery which defended it.
The original 1961 road show release used Technicolor prints made in London, which gave the film eye-popping clarity and disguised many of the imperfections of the sets and special effects. When it came time to turn out mass runs of prints for the general release, Columbia shipped the original negative to a bargain-rate lab in New York, where it was reconfigured for normal Eastmancolor printing. This meant re-cutting the negative to insert standard opticals to approximate the Technicolor process's smooth dissolves, etc. No preservation separations were made and the negative wasn't properly protected. Poor-quality dupe sections were soon patched in to replace damaged pieces of the negative. Eventually two entire reels would have to be replaced in this way, after that New York lab accidentally destroyed the originals through handling errors. Columbia also discarded the film's original sound elements and stereo tracks. A collector's magnetic print was used to recover the original four channel stereo mix.
The screenplay differs drastically from Alistair MacLean's book in terms of characters, including the identity of the traitor and the two women who don't even appear in the novel. The two guides were actually men but the women characters did more or less follow the novel.
Kenneth More was originally cast as Miller but was released from the film (and his contract at Rank) after abusing and swearing at Rank chief John Davis during a BAFTA dinner at the Dorchester. He was replaced by David Niven.
James Darren was cast as Private Spyros Pappadimos in hopes it would get him out of the "teen idol" stage. However, the sequel to Gidget (1959) came out later in the year, starring James Darren as Moondoggie.
Gregory Peck revealed, in a later interview, his bemusement at co-star Anthony Quinn's decision to wear a red undershirt, which was only somewhat revealed through most of the film, but which became a glaring focal point when wet and placed against a most blue and gray background near the end of the movie.
"Yialo Yialo" ("Seashore, Seashore"), heard sung at a wedding celebration, is a Greek folk song about love and the sea. As with many provincial folk songs, verses are often improvised as it's sung. The first verse heard in the film (asking the sea not to wake the singer's beloved) is standard, while the second verse, sung by actor/singer James Darren, is ostensibly improvised. The verse asks the mountains to bow down so that he can see his dearest love, "Anoula", and far-away home, "Rahoula". This improvisation came about as follows. Carl Foreman's production coordinator with the Greek government, Daniel Bourla, who also functioned as the producer of two shorts made on the filming of Guns of Navarone - one directed by 'John Schlesinger' and one by Bourla - tried to obtain an affidavit from the Greek government certifying that Yalo Yalo was in public domain. The certification was issued but it erroneously listed Bourla as its author. Whereupon, Bourla issued a release himself for the use of this song and added a needed additional verse to the song using the name Anoula (Anna being his girlfriend at the time).
Although in the plot Mallory is supposed to be fluent in German, Gregory Peck could not speak the language, and so his German lines are all dubbed by Robert Rietty. Peck was also dubbed when speaking Greek.
During shooting, Gregory Peck and David Niven became close friends, bonding initially over Peck's ability to consume vast quantities of brandy, which the actors used to stay warm while filming in a cold studio tank, without muffing a line. Their families visited each other frequently in later years, and Peck would deliver the eulogy at Niven's funeral.
Stanley Baker's character, Pvt. Brown is referred to as "The Butcher of Barcelona" by Capt Mallory, as a reference to his service with the Republican forces in the Spanish Civil War. In the 1930s, Carl Foreman, the producer and screenwriter of the film, had been a member of the Communist Party, many of whose members fought for the Republic during the Civil War. Foreman was blacklisted during the early 1950s and moved to England, where he continued to work in the film industry. During the period of the blacklist, left-wing supporters of the Spanish Republic often were denounced for being "premature anti-fascists" for having fought against Franco, Hitler and Mussolini before the U.S. went to war against the Axis two years after the collapse of the Spanish Republic.
There had been some concern that the cast would not get along, particularly since Anthony Quinn had a reputation for being difficult to work with. However, in the event things went smoothly, although according to Quinn Stanley Baker did not get along with the others. Some of the cast believed that Baker felt he should have been playing Mallory.
Lead character Mallory is chosen for the mission specifically because of his mountain climbing prowess - the name for the character may well have been based on real-life mountaineer George Mallory, who died trying to summit Mount Everest in 1924 (his body would remain, undiscovered, upon the mountain for another 75 years) Incidentally, real-life Mallory's climbing partner's name was Andrew "Sandy" Irvine, which, if you include the nickname, has the initials of fictional Mallory's partner (A.S. for Andrea Stavrou) in it.
The last sequence shot was the actual setting of the bombs. With three days left to shoot, David Niven was felled by an infection from a split lip sustained shooting in the studio tank. As doctors tried to identify the infection so they could treat it effectively, the production ground to a halt for a month. Finally, Niven defied his doctors' orders and returned to the set to finish the film before he had fully recovered. The relapse that resulted put him in the hospital for seven weeks.
Andreas's revolver that he points at Mallory from behind the newspaper is an Enfield No 2 Mk I* (identifiable as the "*" modification by the lack of the hammer spur). It fired the anemic .380/200 service round and is widely considered to be one of the worst service sidearms ever foisted on an unwilling army.
The film's initial $2 million budget rose quickly thanks to the rigours of location shooting, including filming in areas that were only accessible by donkey and the need to hire 1,000 Greek soldiers to play the German army.
When Mallory says of Stavros: "He's from Crete; those people don't make idle threats", he's inverting the famous quote by the Cretan philosopher Epimenides, that "all Cretans are liars". The end of the movie reveals which of the two is right.
The scene near the end of the movie where the guns fire on the approaching British ships show the gun crew dressed in anti flash gear covering there ears in a synchronised movement. This was used as the basis for the viewing mice in A Grand Day Out (1989) featuring Wallace and Gromitt, where they don their sunglasses as the rocket was taking off.
The team is recruited from various British Army outfits, which is identifiable via their cap badges. Miller (Niven) wears the cap badge of the "Durham Light Infantry" Franklin (Quayle) wears the insignia for the "9th Queen's Royal Lancers". Brown (Baker) wears the insignia for the "Queen's Own Royal West Kent Regiment." Major Baker (Cuthbertson), who houses the team before they head out, wears the "Royal Regiment of Artillery" insignia.
When the team stops the German truck on the road, pretending their own vehicle has broken down, the soldier who peeks through the drape in the back of the truck is Harrison Ford, who was then just 19 years old.
One of the warships in the film, then a training ship in the Hellenic Navy known as Aetos (D-01), was previously the Cannon class destroyer escort USS Slater. The ship was later returned to US and the USS Slater is now a museum ship in Albany, New York.
The trivia item below may give away important plot points.
Once Anna is revealed as the traitor Miller finishes his argument by saying "Q.E.D. "Q.E.D" is an old Greek/Latin phrase, "quod erat demonstrandum", meaning "which is what had to be proven" and was(is) used to drive the point home.