Donald Pleasence had actually been a Royal Air Force pilot in World War II, who was shot down, became a prisoner of war and was tortured by the Germans. When he kindly offered advice to Sturges, he was politely asked to keep his "opinions" to himself. Later, when another star from the film informed Sturges that Pleasence had actually been a RAF Officer in a World War II German POW Stalag camp, Sturges requested his technical advice and input on historical accuracy from that point forward.
James Garner had been a soldier in the Korean War and was twice wounded. He was a scrounger during that time, as is his character Flt Lt Hendley.
Richard Attenborough was an RAF air gunner/photographer who served in the RAF for three years unlike his character, based on Squadron Leader Roger Bushell who was a Spitfire Pilot in 92 Squadron in the early years of World War Two.
Several cast members were actual P.O.W.s during World War II. Hannes Messemer was held in a Russian camp and Til Kiwe and Hans Reiser were prisoners of the Americans.
Executive Meddling: Early on in the production, Sturges began receiving memos from distributor United Artists requesting female roles in the picture. One even suggested having the dying Ashley-Pitt cradled in the lap of a beautiful girl in a low-cut blouse. The studio wanted to cast this bit by having a Miss Prison Camp contest in Munich. Sturges would have none of it.
Hostility on the Set: Richard Attenborough said many years later working with Steve McQueen on this film was one of the toughest challenges he had ever faced and their on set relationship was not peaceful. McQueen was not combative but he wouldn't hesitate to let anyone know if things were not as he would wish them to be or believed that they ought to be.
Wag the Director: The motorcycle chase was added at the insistence of Steve McQueen, who signed onto the film on the condition that he show off his biking skills. After viewing the rushes, McQueen decided his part was minor and undeveloped. He was particularly upset that his character virtually disappears from the film for about thirty minutes in the middle so he walked out demanding rewrites. John Sturges admitted the half-hour gap was likely a problem, but with the production already behind schedule due to the heavy rain, he felt he couldn't take time out to do rewrites and rescheduling. James Garner said he and James Coburn got together with McQueen to determine what his specific gripes were. Garner later said it was apparent McQueen wanted to be the hero but didn't want to be seen doing anything overtly heroic that contradicted his character's cool detachment and sardonic demeanor. At the same time, McQueen never really liked his character's calm acquiescence to his time in the cooler or the famous bit with the catcher's mitt and ball. Sturges considered writing the character out of the story altogether, but United Artists informed him they considered McQueen indispensable to the picture's success and would spring for the extra money to hire another writer, Ivan J. Moffitt, to deal with the star's demands. McQueen returned to work.
Richard Harris was originally cast as Roger Bartlett, but dropped out because filming This Sporting Life was behind schedule and he was displeased with the diminished role of Big X after script changes had been made.
Writing by the Seat of Your Pants: According to John Sturges, the screenplay went through six writers and eleven versions, and was still a work in progress during the actual shooting. "I'm not proposing that's a good way to make a picture, but it was the right way to make this one," he later said.