In June 1934, he left the SA to join the
SS (#107,426) instead, under the advice of a friend who told him that SS membership would help him get into the police. However, he appealed the decision, and was allowed to enter the officer training scheme at
Braunschweig. Initially he failed, but, following another appeal, was given a second chance, and at 26 passed the course and was given a trial run as an SS officer. When Esterwegen was closed in 1936, he was transferred to a unit near
Sachsenhausen concentration camp before being sent for
Wehrmacht training, and was sent to the front when the
Second World War broke out. Hassebroek's reports improved significantly whilst he was at war, and in 1942, he was promoted to
Hauptsturmführer, his first promotion. ==Concentration camp commandant==