[3] In 1935, Bretnütz transferred to the newly formed Luftwaffe and received flight and fighter pilot training at Döberitz.

Following the creation of I. Gruppe (1st group) of Jagdgeschwader 334 (JG 334—334th Fighter Wing) at Mannheim-Sandhofen Airfield in 1937, Bretnütz was posted to 1.

[6] In Spain, he claimed two aerial victories, a Polikarpov I-15 fighter on 6 November 1938, and a Tupolev SB-2 bomber on 28 December.

[11] World War II in Europe began on Friday, 1 September 1939, when German forces invaded Poland.

Staffel on a mission which intercepted French Curtiss P-36 Hawk fighters, escorting a reconnaissance aircraft, near Bad Bergzabern.

[14] On 31 March 1940, Bretnütz claimed two Morane-Saulnier M.S.406 fighters near Saargemünd during an afternoon aerial encounter and a Vickers Wellington bomber that evening.

One of the Hurricanes was probably flown by Flight Lieutenant James Brindley Nicolson who was shot that day and Pilot Officer Martyn King.

[18] On 20 October, Bretnütz made a forced landing in his Bf 109 E-7 (Werknummer 4112—factory number) near Saint-Inglevert following damage sustained during aerial combat.

[19] That day, he had claimed a Hawker Hurricane fighter shot dow, his twentieth aerial victory of World War II.

Two days later, he traveled to the headquarters of Hermann Göring, the Commander-in-Chief of the Oberkommando der Luftwaffe (Air Force High Command), for the presentation of the Knight's Cross.

[21] The Gruppe was withdrawn from the Channel Front on 20 December 1940 and transferred to Köln-Butzweilerhof Airfield for a period of rest and replenishment.

[22] The bulk of the Geschwader's air elements were moved via Jever, in northern Germany, to Mannheim-Sandhofen Airfield on 8 June 1941.

Gruppe was transferred to Neusiedel in East Prussia, present-day Malomožaiskojė in Kaliningrad Oblast in Russia, between 12–14 June.

In this aerial battle, his Bf 109 F-2 (Werknummer 6674) was hit by the bombers return fire, damaging the aircraft and injuring him.

His mother and wife later travelled to Insterburg and had his body cremated, taking his remains to Mannheim where he was reinterred on the family grave.