As Wilhelm studied at the Vienna War College, there began the World War I. Upon graduation in 1915 he went to the frontlines starting his military service in a company of the 13th Galicia Lancer (Ulan) Regiment. The regiment was dominated by Ukrainians around Zoloczow (Zolochiv). While serving in the regiment Wilhelm started to read works of Mykhailo Hrushevsky, Ivan Franko, Taras Shevchenko and others. His soldiers gave him as a present a Ukrainian embroidered shirt-vyshyvanka which he carried under his uniform. Habsburg asked his soldiers to call him Vasyl and later for the embroidered shirt was nicknamed as Vyshyvanyi. During that period he repeatedly had to defend the Galician Ukrainians whom the local administration consisted predominantly of Poles were arresting under suspicion of disloyalty to Austria-Hungary.