On 5 July, Mietusch arrived at Cuxhaven-Nordholz Airfield where III. "Gruppe" was based and took over command from Hermichen. In July, the "Gruppe" received the Bf 109 G-4 and G-6 variants and the pilots began familiarizing themselves with this aircraft type while flying in Defense of the Reich. On the night of 24/25 July, the RAF and USAAF launched Operation Gomorrah, the attack on Hamburg during the last week of July 1943. The RAF initiated the attack at night which created a firestorm in the city. The following day, the USAAF attacked Hamburg with 100 B-17 bombers, spreading the destruction. Further 118 B-17 bombers bombed Kiel that day. Defending against these attacks, Mietusch claimed his first aerial victory as "Gruppenkommandeur" when he shot down a B-17 north of Hamburg. The USAAF targeted the German aircraft industry on 17 August in the Schweinfurt–Regensburg mission. Mietusch led his "Gruppe" against the bombers and shot down two B-17 bombers, the first southeast of Schleiden in the Eifel hills, and the second south of Laacher See. On 29 November, VIII Bomber Command attacked Bremen. III. "Gruppe" intercepted the bombers prior to their bomb run and Mietusch shot a B-17 from its combat box west of Oldenburg. This was referred to as a "Herausschuss" (separation shot) and denoted a severely damaged heavy bomber which was forced to separate from its combat box and was counted as an aerial victory.