on 23 December 1938. Initially serving as a pilot and Staffeloffizier (squadron officer) in Jagdgeschwader 2 "Richthofen" (JG 2—2nd Fighter Wing), named after the after World War I fighter ace Manfred von Richthofen, he was promoted to Oberleutnant (first lieutenant) on 1 June 1939. He then held the position of Technischer Offizier (technical officer) with Stab of Jagdgruppe 176 (176th Fighter Group), which was formed from the II. Gruppe (2nd Group) of Zerstörergeschwader 76 (ZG 76—76th Destroyer Wing). In mid 1939, Joppien was posted to the 1. Staffel (1st Squadron) of Jagdgeschwader 51 (JG 51—51st Fighter Wing). World War II World War II in Europe began on Friday, 1 September 1939, when German forces invaded Poland. On 23 November 1939, on the Western Front, Joppien claimed his first victory, an Armée de l'Air (French Air Force) Morane-Saulnier M.S.406 of GC III/7, piloted by Sergent (Sergeant) Guillaume who crash landed at Heillecourt where the aircraft completely burned out. During the encounter, his Messerschmitt Bf 109 was damaged by enemy fire resulting in undercarriage failure on landing. His aircraft overturned, fortunately for Joppien, he escaped unhurt. For this achievement, he was awarded the Iron Cross 2nd Class () on 13 December 1939. Battle of France and Britain The Battle of France, the German invasion of France and the Low Countries, began on 10 May 1940. During this campaign, Joppien was awarded the Iron Cross 1st Class () on 10 June 1940. By 25 June 1940, the date which marked the end of the French campaign, he claimed three further victories, which brought his total to four aerial victories. On 10 June, I. Gruppe was ordered to Jever Airfield and to Leeuwarden Airfield on 21 June. The Gruppe was then ordered to Saint-Inglevert Airfield on 12 July and participated in the Battle of Britain against the Royal Air Force (RAF). On 5 August 1940, Joppien became Staffelkapitän (squadron leader) of the 1. Staffel (1st squadron) of JG 51. He succeeded Hauptmann Douglas Pitcairn who was injured in a takeoff accident that day. He claimed his first aerial victory as a Staffelkapitän on 11 August. That day, the Gruppe encountered RAF Supermarine Spitfire fighters off of Dover. During these battles, after 21 aerial victories claimed, he was awarded the Knight's Cross of the Iron Cross () on 16 September 1940. Two days later, he was promoted to Hauptmann (captain). He accumulated further victories against