P.R. Reid wrote three books on Colditz: "The Colditz Story" (1952) and "The Latter Days at Colditz" (1953). The earlier book, based largely on Reid's own experiences, was the basis for the film. In 1984, Reid also published "Colditz: The Full Story," a less personal and more thoroughly researched account of Colditz during WWII.
According to the film, the first British soldier to escape from Colditz Castle was Lieutenant Colonel Airey Neave D.S.O OBE MC who made the British Home Run in January 1942.
According to the movie's epilogue, prior to the liberation of Colditz during April 1945, there were a total of 320 escape attempts from Colditz Castle. Of these, there were 56 successful escapes (5 Polish; 14 British; 15 Dutch; and 22 French). The film maintains that this was "a record unequaled in any P.O.W. camp in the two world wars".
Anthony Faramus, billed here as a "British Officer" prisoner, actually was a prisoner of Germany during World War II, though not at Colditz. He was arrested in the Channel Islands early in the war, as a saboteur. He spent the remainder of the war in various German prisons, including Buchenwald and Mathausen concentration camps. He wrote about his ordeals in the book "The Faramus Story." He was also closely associated with British double agent Eddie Chapman.
The character portrayed by John Mills, Capt. Patrick Reid, is based on P.R. Reid, author of the novel on which the film was based. Reid, imprisoned at Colditz 1940-42 until his successful escape, also was technical consultant on the film. The German security officer, Paul Priem, also is portrayed (by Denis Shaw) under his actual name. Priem had died in 1943. All the other character names were invented for the film.
The large outer courtyard of Colditz Castle which can be seen in the film is known as the Kommandantur.
The song sung by the POWs in the theatrical revue towards the film's end, "I Belong to Colditz", is a parody of one of Will Fyffe's signature songs, "I Belong to Glasgow." The sequence also parodies Flanagan and Allen's double-act, including the song, "Underneath the Arches" Refer - Bud Flanagan and Chesney Allen.