During the Second World War, when the company was chaired by Nazi Party activist Wilhelm Zangen, slave labour was employed at their tube rolling mills.Wistrich, Robert S. (2001). Who's who in Nazi Germany (3 ed.). Routledge, p. 183 Zangen served four months in prison for his involvement, although he remained a leading figure with Mannesmann until his retirement in 1966.S. Jonathan Wiesen, West German Industry and the Challenge of the Nazi Past, 1945-1955, UNC Press Books, 2004, p. 28
