[Note 1] That day, he was also promoted to Leutnant (second lieutenant) and transferred to Kampfgeschwader 138 (KG 138–138th Bomber Wing).

[2] World War II in Europe had begun on Friday, 1 September 1939, when German forces invaded Poland.

Bauer claimed his first aerial victory on 15 May 1940 west of Bruges, a Royal Air Force (RAF) Hawker Hurricane.

[6] Bauer was promoted to Oberleutnant (first lieutenant) on 1 June 1940 and was awarded the Iron Cross 1st Class (Eisernes Kreuz 1.

Gruppe was withdrawn from the English Channel and relocated to Gütersloh Airfield for a period of rest and replenishment.

Gruppe spent a couple of days of R&R skiing in the Kleinwalsertal before returning for active service on 17 March.

Staffel (9th squadron) of JG 3, succeeding Oberleutnant Max Jaczak who killed in a flying accident the day before.

Gruppe supported Army Group South in its strategic goal towards the heavily populated and agricultural heartland of Ukraine, taking Kiev before continuing eastward over the steppes of southern USSR to the Volga with the aim of controlling the oil-rich Caucasus.

[13] On 23 July 1941, Bauer claimed two Polikarpov I-153 biplane fighters shot down, taking his to total to 36 aerial victories.

[14] That afternoon, his Bf 109 F-2 (Werknummer 8987—factory number) sustained heavy damage in combat with a flight of Ilyushin DB-3 bombers at the Dnieper.

Gruppe of JG 3 had been redeployed to an area of operations north of Lake Ilmen in support of the airlift resupplying German forces in the Demyansk Pocket.

[18] In combat with 6 Udarnaya Aviatsionnaya Gruppa (6 UAG—6th Soviet Strike Aviation Group) on 4 April, he claimed his 50th aerial victory, a Lavochkin-Gorbunov-Gudkov LaGG-3 fighter.

[23] Bauer and together with Oberleutnant Erwin Clausen were presented the Oak Leaves by Adolf Hitler at the Führerhauptquartier at Rastenburg.

[25] On recovery, Bauer was put in command of Ergänzungs-Jagdgruppe Ost (Supplementary Fighter Group, East) in southern France on 9 August 1943.