After he completed flight training, Gildner was posted to an aerial reconnaissance unit where he served as a pilot. In the fall of 1938, he was posted to the 6. Staffel (6th Squadron) of Jagdgeschwader 132 "Richthofen" (JG 132—132nd Fighter Wing), named after the World War I fighter ace Manfred von Richthofen. This squadron was subordinated to the II. Gruppe (2nd group) of JG 132. On 1 November 1938, II. Gruppe was detached from JG 132 and was reassigned as I. Gruppe of Zerstörergeschwader 141 (ZG 141—141st Destroyer Wing). I./ZG 141 was based at Jüterbog-Damm and was equipped with the Messerschmitt Bf 109 D-1. On 1 May 1939, I./ZG 141 was renamed again and became the I. Gruppe of Zerstörergeschwader 1 (ZG 1—1st Destroyer Wing) and was the equipped with the Messerschmitt Bf 110 heavy fighter. World War II World War II in Europe had begun on Friday 1 September 1939 when German forces invaded Poland. Flying with I./ZG 1, Gildner participated in the invasion of Poland and the Norwegian Campaign. In February 1940, I./ZG 1 was placed under the command of Hauptmann (Captain) Wolfgang Falck. With the start of the Norwegian Campaign in April 1940, I./ZG 1 was moved to Aalborg airfield. There, the airfield came under night attacks by the Royal Air Force (RAF) Bomber Command, leading Falck to conduct his first experiments of nocturnal aerial combat. During the Battle of France, Gildner claimed his first aerial victory on 10 May 1940 over a Bristol Blenheim bomber in the vicinity of Waalhaven. His second and last daytime aerial victory was claimed over a French Morane-Saulnier M.S.406 fighter on 5 June 1940. Night fighter career Following the 1939 aerial Battle of the Heligoland Bight, RAF attacks shifted to the cover of darkness, initiating the Defence of the Reich campaign. By mid-1940, Generalmajor (Brigadier General) Josef Kammhuber had established a night air defense system dubbed the Kammhuber Line. It consisted of a series of control sectors equipped with radars and searchlights and an associated night fighter. Each sector named a Himmelbett (canopy bed) would direct the night fighter into visual range with target bombers. In 1941, the Luftwaffe started equipping night fighters with airborne radar such as the Lichtenstein radar. This airborne radar did not come into general use until early 1942. Following the Battle of France, Falck was tasked with the creation of the Luftwaffe's first night fighter wing,