Like his father before him, Cade left his young family to fight for Australia in the Armed Forces in World War II. Cade was appointed captain, Australian Army Medical Corps, A.I.F., on 1 July 1940 and posted to the 2nd/9th Field Ambulance. Although trained as a psychiatrist, Dr. Cade served as a surgeon and departed for Singapore in 1941 on RMS Queen Mary. He was promoted to major in September 1941. After the Fall of Singapore to Japan, he became a prisoner of war at Changi Prison from February 1942 to September 1945. During his imprisonment, he reportedly would observe some fellow inmates having strange, vacillating behaviour. He thought perhaps a toxin was affecting their brains and when it was eliminated through their urine, they lost their symptoms.