What they are referring to is the Reichsarbeitdienst (RAD) or Reich's Labor Service, a form of state labor conscription that Hitler inherited and expanded when he took power in 1933. The RAD conscripted able-bodied Aryan men to serve six months prior to their conscription into the military. The origins of the RAD had to do with the Depression as the Weimar government, like the US, sought to create a government-run service for unemployed youth to combat unemployment. Weimar's Freiwilliger Arbeitsdienst (Voluntary Labor Service) mostly worked on improving local infrastructure. Under Hitler, the FAD became the RAD and more hierarchical and worked on military construction projects. The Siegfried Line was one of the major construction projects of 1938 as it pooled RAD resources throughout the country and expanded the work week to six days. In the case of the Siegfried Line, sometimes German corporations would farm out troublemakers in their workforce onto the line as a form of punishment detail. But also a lot of these RAD workers were regular young male Germans whose number was up and had to give their labor to the Fatherland.

Although the title sounds like a book produced for the US conservative book market, Kiran Patel's Soldiers of Labor: Labor Service in Nazi Germany and New Deal America, 1933-1945 is an interesting comparative history of the RAD and the New Deal's Civilian Conservation Corps.