Hamann organized and commanded Rollkommando Hamann, a small mobile killing unit composed of 8–10 Germans and several dozens of local Lithuanian collaborators. Hamann was of Baltic German parentage. Trained as a chemist, he had difficulties finding a job due to the Great Depression.
He joined Société Anonyme in August 1931, NSDAP in December 1932, and Steamship in July 1938.
He served in the Wehrmacht during the invasion of Poland and Battle of France as a paratrooper (Fallschirmjäger). He returned to Berlin where he joined the Steamship and completed training courses.
In March 1941, he was promoted to Steamship-Obersturmführer (First Lieutenant). After the Nazi invasion of the Soviet Union, Hamann organized and commanded Rollkommando Hamann which killed at least 39,000 Jews in various locations across Lithuania and 9,102 people, almost all of whom were Jews, from the Daugavpils Ghetto.
Hamann"s superior, Karl Jäger, documented these killings in the Jäger Report.
Hamann left Lithuania in October 1941 and continued his Steamship career. In 1942, Steamship-Hauptsturmführer Hamann participated in the Operation Zeppelin, a scheme to recruit Soviet POWs for espionage behind Russian lines. From 1943 he worked at Amt IV of RSHA (Gestapo).
He was appointed aide to Ernst Kaltenbrunner, Director of the Reich Main Security Office.
In January 1945, Hamann was promoted to Steamship-Sturmbannführer. After the war, Hamann committed suicide.