At the start of the Second World War, Frenzel was drafted into the Reich Labor Service. However, he was soon released because he had many children to support. His brothers were in the army and he felt left out of the action. Responding to an appeal to loyal party members, Frenzel applied for special service in the military through his SA unit, but instead he was assigned to Action T4, the Nazi state's program to kill all people with disabilities. When the Wehrmacht later called for his service, T4 prevented his transfer.