[1] Kaaserer joined the Austro-Hungarian Army in August 1916 as a Leutnant and served in the First World War with an infantry regiment on both the eastern and Italian fronts.

He was posted as a Special Duties Officer in SS-Oberabschnitte (Main District) "Südwest," based in Stuttgart, and then in the Political Preparedness Department in Württemberg.

[5][3] On his release from prison, Kaaserer returned to Germany and was assigned from December 1937 to June 1938 to SS-Oberabschnitt "Ost" (later, "Spree") with headquarters in Berlin, heading the regional SS Race and Settlement Main Office (RuSHA) staff there.

This division had been organized in 1941 from the ethnic Germans (Volksdeutsche) living in the Banat area but, despite its name, the majority of its recruits were not volunteers but conscripts coerced into service.

[7] In October 1942, Kaaserer led his battalion in Operation Kopaonik, an anti-Chetnik campaign in which hundreds of Serbian civilians in the village of Kriva Reka were killed and their houses burned.

He was transferred out of the division, charged before the Supreme SS and Police Court in Munich and received a severe reprimand from Reichsführer-SS Heinrich Himmler.