the new, more powerful Messerschmitt Bf 109 F-4 model. On 21 June 1941, the Gruppe was ordered to Mizil in preparation of Operation Barbarossa, the German invasion of the Soviet Union. Its primary objective was to provide fighter protection for the oil fields and refineries at Ploiești. The invasion of the Soviet Union began on 22 June. The next day, the Gruppe moved to Mamaia, the northern district of Constanța on the Black Sea coast. There, Köppen claimed his first two aerial victories on 24 June. He was credited with shooting down two Soviet Ilyushin DB-3 bombers in the morning near Constanța. Two days later, he again claimed two DB-3 bombers in that combat area. The Gruppe moved to Belaya Tserkov on 1 August and also used an airfield at Yampil from 6 to 8 August. There, Köppen claimed a Polikarpov I-16 fighter on 2 August and another I-16 fighter on 4 August near Kiev. On 6 August, he claimed an aerial victory over Polikarpov I-16 fighter. Three days later, two Tupolev SB-2 bombers were claimed by him followed by two further SB-2 bombers on 17 August. He claimed his twelfth aerial victory on 19 August over a Mikoyan-Gurevich MiG-3 fighter. This put him in second place within III. Gruppe with respect to number of aerial victories claimed, one behind his Staffelkapitän (squadron leader) Oberleutnant Günther Rall. On 27 August, III. Gruppe had reached an airfield named Stschastliwaja located approximately east-southeast of Oleksandriia. In the early morning of 2 September, elements of III. Gruppe moved to Myronivka where they escorted Junkers Ju 87 dive bombers heading for Novomoskovsk. Near Kremenchuk on the Dnieper, Köppen claimed two Vultee V-11 attack aircraft shot down. On 12 September, 8. and 9 Staffel moved to an airfield at Beryslav, staying there for three days. Here, Köppen claimed two Polikarpov I-153 fighters shot down, one on 13 September and another the next day. By 23 September, Köppen had increased his number of aerial victories to 17. The next day, III. Gruppe moved to the Poltava Air Base, supporting the 17th Army in the First Battle of Kharkov. Köppen's total number of aerial victories stood at 31 on 23 October, making him the leading fighter pilot of III. Gruppe at the time. On 2 November, the Gruppe moved to Taganrog where they stayed until 1 January 1942. On 18 December 1941, Köppen was awarded the Knight's