At the outbreak of World War I, Weber, aged 50, volunteered for service and was appointed as a reserve officer in charge of organizing the army hospitals in Heidelberg, a role he fulfilled until the end of 1915.[11][17] Weber's views on the war and the expansion of the German empire changed during the course of the conflict.[16][17][18] Early on, he supported nationalist rhetoric and the war effort, though with some hesitation, viewing the war as a necessity to fulfill German duty as a leading state power. In time, however, Weber became one of the most prominent critics of German expansionism and of the Kaiser's war policies.[6] Weber publicly attacked the Belgian annexation policy and unrestricted submarine warfare, later supporting calls for constitutional reform, democratisation, and universal suffrage.[6]