From August 1943, Bartels served with 11. "Staffel" of "Jagdgeschwader" 27 "Afrika" (JG 27—27th Fighter Wing). This "Staffel" was subordinated to the newly created IV. "Gruppe" of JG 27. The "Gruppe" had been formed in May 1943 at the Kalamaki Airfield in Athens, Greece under the command of "Hauptmann" Rudolf Sinner. 11. "Staffel" was commanded by "Oberleutnant" Alfred Buk. On 17 July, IV. "Gruppe" moved to Tanagra Airfield. Bartels claimed his first aerial victories with JG 27 on 1 October. Flying from Gadurrà Airfield on Rhodes, he claimed two Douglas A-20 Havoc bombers, also known as Bostons, near of Kos. In early October, the United States Army Air Forces (USAAF) flew many missions in support of British forces fighting in the Dodecanese campaign. On 5 October, IV. "Gruppe" intercepted a flight of Consolidated B-24 Liberator bombers over the northern Attica. In this encounter, Bartels claimed the destruction of two B-24 bombers. Three days later, 105 USAAF aircraft attacked German airfields in Greece. IV. "Gruppe" encountered the escort fighters and shot down three Lockheed P-38 Lightning fighters, all of them credited to Bartels.