During the Second World War Pleasence was initially a conscientious objector, but later changed his stance and was commissioned into the Royal Air Force, serving with 166 Squadron, RAF Bomber Command. His Lancaster NE112 was shot down on 31 August 1944, during a raid on Agenville. He was taken prisoner and placed in the German prisoner-of-war camp Stalag Luft I, where he produced and acted in plays. He would later play Flight Lieutenant Colin Blythe in The Great Escape where much of the story takes place inside a German POW camp.
During the last year of the war, he spent his time being beaten and mentally tortured by sadistic Nazi guards, while dreaming of the day that would bring him freedom. This day came in 1946, when he was recovered from the P.O.W. camp and discharged with the rank of flight lieutenant.
Lt. Pleasence, we salute you for your service. R.I.P.