Wilhelm Ritter von Thoma was born in Dachau in 1891 as son of a Bavarian tax official and became career officer with the Bavarian Army. Thoma took part in the first World War with 3rd Bavarian Infantry Regiment (part of 2nd, then, from 1915, 11th Bavarian Infantry Division) on the Western (1914/15/16/17/18) and Eastern Front (1915/16), the Serbian Campaign (1915) and the Romanian Front in 1916/17. During the Second Battle of the Marne in July 1918 he was captured by French-American forces and became Prisoner of war until September, 1919.