Brändle, who already was a civilian motor-powered aircraft and glider pilot, volunteered for military service in the Luftwaffe of Nazi Germany in 1935. He was posted to Jagdgeschwader 53 (JG 53—53rd Fighter Wing) under command of Oberstleutnant Werner Junck, in 1939 and claimed 14 aerial victories on the Western Front. In May 1942 he was given command of II. Gruppe (2nd group) of Jagdgeschwader 3 “Udet” (JG 3—3rd Fighter Wing). Fighting on the Eastern Front, he was awarded the Knight’s Cross of the Iron Cross on 01-07-1942 after 49 aerial victories. In July and August 1942, he claimed a further 50 aerial victories in the southern sector of the Eastern Front. After claiming his 100th aerial victory he was awarded the Knight’s Cross of the Iron Cross with Oak Leaves on 27-08-1942.
On 05-07-1943 during the Battle of Kursk, Brändle achieved his 150th aerial victory and in August 1943 was transferred to the Western Front fighting in Defense of the Reich.