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.
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.
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.
Wildfrid Bonnin, the Public Health Inspector for the London Borough of Lambeth, went to inspect the mobile canteen catering for 100 workers on location. He was pleasantly surprised to discover what they were filming, as he used to be an air raid warden with Violette's father.
Director Lewis Gilbert and producer Daniel M. Angel wanted a double to be used for the jump from the parachute training tower, but Virginia McKenna insisted on doing it herself. Slowed slightly by a wire (as are all trainee parachutists) she landed with a professional-looking roll on the mat below. Picking herself up, she smiled and said "That was fun. I'd like to do it again."