"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).

Gregory Peck declined to attempt an English accent in order to play Captain Mallory.

Gregory Peck often said he was disappointed that so many viewers had missed how anti-war the film was intended to be.

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.

Dean Martin and Alec Guinness were considered for David Niven's role.

Rock Hudson was considered for Gregory Peck's role. Cary Grant was also briefly considered, but was rejected as being too old at 56.

William Holden asked for $750,000 plus 10% of the gross to play Mallory. He was turned down and Gregory Peck was cast.

Anthony Quinn was always Carl Foreman's first choice to play Stavros.

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.

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.

Anthony Quayle spent part of WWII in Albania organizing guerilla forces.

J. Lee Thompson's handling of intimate drama on Tiger Bay and of large scale action setpieces on North West Frontier landed him the director gig.

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' came out later in the year, starring James Darren as Moondoggie.

James Darren was concurrently on honeymoon during filming.

David Niven initially felt that he was badly miscast in the offbeat role of a corporal, but later said he considered it to be one of his best performances despite being too old for the part.

David Niven wears a Light Infantry cap badge on his beret. This was the regiment he was commissioned into in WW2.

80s rock group Big Country borrowed from Dimitri Tiomkin's score to create the guitar riff on their hit "Fields of Fire".

According to the 50th anniversary book about the RAF's Battle of Britain Memorial Flight the Flight's Lancaster appeared in the film.

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.

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.