Following the outbreak of World War II, Thiele joined the Militia and served as a signaller. Interested in becoming a pilot, he transferred to the Royal Australian Air Force (RAAF) on 10 October 1942. He graduated from flying school the following year and was commissioned as officer. In 1944, Thiele was posted to the Mediterranean theatre, where he served with No. 458 Squadron RAAF, a maritime patrol/strike unit, flying Vickers Wellingtons, from bases at Foggia, Italy, and Gibraltar. He was promoted to Flight Lieutenant in September 1945 and was discharged on 16 January 1946, after returning to Australia.