Schmidt planned to study without interruption, therefore volunteered at age 18 for military service in 1937. He began serving with an anti-aircraft battery of Luftwaffe at Vegesack near Bremen. In World War II, after brief service on the Eastern Front during the invasion of the Soviet Union in 1941 (including the Siege of Leningrad), he returned to Germany in 1942 to work as a trainer and advisor at the Ministry of Aviation. During his service in World War II, Schmidt was awarded the Iron Cross 2nd Class. He attended the People's Court as a military spectator at some of the show trials for officers involved in the 20 July plot, in which an unsuccessful attempt was made to assassinate Hitler at Rastenburg, and was disgusted by Roland Freisler's conduct. Toward the end of the war, from December 1944 onwards, he served as an Oberleutnant in the Flakartillery on the Western Front during the Battle of the Bulge and the Ardennes Offensive. He was captured by the British in April 1945 on Lüneburg Heath, and was a prisoner of war until August of that year in Belgium. In 1958 Schmidt was promoted to Hauptmann of the Bundeswehr reserve.