Romanian Air Force personnel. Here, the trio of Füllgrabe, Graf and Grislawski were joined by Ernst Süß, and later by Leopold Steinbatz and Edmund Roßmann. War against the Soviet Union Following its brief deployment in the Balkan Campaign, III. Gruppe was back in Bucharest by mid-June. There, the unit was again subordinated to the Luftwaffenmission Rumänien and reequipped with the new, more powerful Bf 109F-4 model. On 21 June, 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. Prior to the invasion, Handrick was replaced by Major Albert Blumensaat as commander of III. Gruppe. Blumensaat was then replaced by Hauptmann Hubertus von Bonin on 1 October. At the time, von Bonin was still in convalescence so that Hauptmann Franz Höring, the commander of 9. Staffel, was also made the acting Gruppenkommandeur (group commander). On 22 July 1942, the Geschwaderkommodore (wing commander) of JG 52, Major Herbert Ihlefeld, was severely injured in a flight accident and had to surrender command during his convalescence. In consequence, Major Gordon Gollob, the commander of Jagdgeschwader 77 (JG 77—77th Fighter Wing), temporarily took over command of JG 52 as acting Geschwaderkommodore. On 17 August, Gollob was ordered dispatch one Schwarm, a flight of four aircraft, of every III. Gruppe squadron to the Don-bend. The pilots selected for this mission included Füllgrabe, Graf and Süß. Defense of the Reich In response to political humiliation caused by de Havilland Mosquito bombing raids into Germany, Reichsmarschall Hermann Göring, the commander-in-chief of the Luftwaffe, ordered the formation of two specialized high-altitude Luftwaffe units. These units were Jagdgeschwader 25, commanded by Major Herbert Ihlefeld, and Jagdgeschwader 50, commanded by his friend Graf. Graf was permitted to choose his personnel and had his friends Füllgrabe, Grislawski and Süß transferred from III. Gruppe of JG 52. In December 1943, he was posted to Ergänzungs-Jagdgruppe Ost (Supplemantary Fighter Group East) as fighter pilot instructor. On 10 January 1944, the United States Army Air Forces targeted the Luther-Werke, at the time a factory of the Messerschmitt Bf 110, Messerschmitt Me 210 and Messerschmitt Me 410, in Braunschweig, and the aircraft repair works in Waggum, a district of Braunschweig. The 3rd Bombardment Division sent 169 bombers, escorted by 466 fighter aircraft. Defending against this attack, Füllgrabe shot down one of