the RAF and on account of his 40th victory achieved on 21 April was honorably mentioned in the Wehrmachtbericht propaganda radio report, the first of three such mentions, on 22 April. The next day, he was the 11th officer or soldier of the Wehrmacht honored with the Knight's Cross of the Iron Cross with Oak Leaves () which was presented to him by Adolf Hitler. On 18 October, Joppien was appointed Gruppenkommandeur (group commander) of I. Gruppe of JG 51. He succeeded Oberleutnant Richard Leppla who had temporarily led the Gruppe after its former commander, Hauptmann Hans-Heinrich Brustellin had taken been transferred. The Gruppe was withdrawn from operations at the English Channel on 25 May 1941 and relocated to Krefeld Airfield for a short period of maintenance and overhaul. Operation Barbarossa and death In June 1941, JG 51 and the majority of the Luftwaffe were transferred to the Eastern Front in preparation for Operation Barbarossa, the invasion of the Soviet Union on 22 June 1941. There, on 30 June 1941, he shot down five Soviet bombers near Bobruysk in eastern Belarus, his aerial victories 47–51. This "ace-in-a-day" achievement earned him his second mention in the Wehrmachtbericht on 1 July 1941. On 5 July 1941, he was wounded following his 58th victory claimed and spent several weeks in convalescence. On 25 August 1941, Joppien and his wingman, Leutnant Erwin Fleig, engaged in combat with Soviet fighters and bombers near Yelnya, Bryansk Oblast, a village in Krasnovichsky Selsoviet of Unechsky District of Bryansk Oblast, southwest of Bryansk. In the subsequent action Joppien was shot down and killed in his Messerschmitt Bf 109 F-2 (Werknummer 9670—factory number) "Black" by a Soviet Polikarpov I-16 fighter. Fleig later gave to protocol that he and Joppien had attacked three Petlyakov Pe-2 bombers, escorted by three I-16 fighter aircraft, at an altitude of . Fleig saw that Joppien had attacked a Pe-2 bomber, which trailing smoke, was going down. Fleig then observed Joppien's Bf 109 making a sharp right turn and crashed into the ground. By this date, Joppien had shot down 70 enemy aircraft claimed in roughly 270 combat missions. The Wehrmachtbericht announced his death on 29 August 1941. Following his death, command of I. Gruppe went to Hauptmann Wilhelm Hachfeld who had previously commanded 2. Staffel. Summary of career Aerial victory claims According to US historian David T. Zabecki, Joppien was credited with 70 aerial