Mölders joined the Luftwaffe, the air force of Nazi Germany, in 1934. In 1938, he volunteered for service in the Condor Legion, which supported General Francisco Franco's Nationalist side in the Spanish Civil War, and shot down 14 aircraft. With the start of World War II, he took part in the "Phoney War", Battle of France, and the Battle of Britain. With his tally standing at 68 victories, Mölders and his unit, the "Jagdgeschwader" 51 (JG 51), were transferred to the Eastern Front in June 1941 for the opening of Operation Barbarossa, achieving 101 victories by mid-July 1941.