Klöpper was born on 9 January 1918 in Größ Bülten, present-day part of Ilsede, at the time in the Province of Hanover within the German Empire.

Staffel of JG 77 engaged five Armée de l'air Morane-Saulnier M.S.406 fighters west of Dinant.

[3] On the first day of Operation Barbarossa, the German invasion of the Soviet Union on 22 June 1941, he claimed his first victory on the Eastern Front, when he shot down a Russian SB-3 bomber.

The combat occurred at an altitude of 9,000 meters (30,000 feet) in the area of Groningen, Leeuwarden and Meppel, ending over the Zuiderzee.

Following this encounter, Klöpper crashed his Bf 109 G-6 (Werknummer 410 106—factory number) southwest of Meppel after flying through a low cloud cover.

[7] During his career, he shot down a total of 94 enemy planes in approximately 500 combat missions (18 victories were on the Western Front), of which eight were four engined bombers and seven Il-2 Sturmoviks.