Of the 92 days she spent filming, Virginia McKenna only had two days off from the rigorous schedule which included getting up at 5:30 each morning. The two days off were to marry Bill Travers and have a very brief honeymoon.
Technical advisor Leo Marks was in charge of the codes and ciphers for all S.O.E. Agents during the war, when he was only 20. Some have suggested that the Paul Scofield character is loosely based on Marks.
After firing machine guns, jumping from a parachute training platform, spending weeks learning unarmed combat, wading through an ice cold lake at night, spending many hours doing physical jerks and cross country runs, there was one thing that made Virginia McKenna scream with terror: a cockroach in a pile of vegetables.
Sir Michael Caine appears briefly as one of the prisoners on the train. As Violette (Virginia McKenna) starts to escape, he leans forwards and calls out for water.
"The Life That I Have" was written by Leo Marks, an English cryptographer. It was used as a poem code in World War II. During the war, published poems were often used for encrypting messages, but since the original sources could be found by enemy crypt-analysts, the code was easily broken. By writing his own creation, Marks was able to counter the enemy's actions. The poem was issued by Marks to Violette Szabo. It was written by him on Christmas Eve 1943 in memory of his girlfriend, Ruth, who had recently died in a plane crash. Marks, who became a scriptwriter after the war, would only let the poem be used on condition that his authorship was not revealed.