 At the start of World War I , Körös was based at Zemun , just upstream from Belgrade on the Danube . Her commander was Linienschiffsleutnant ( LSL ) Josef Meusburger , and she was accompanied by another three monitors and three patrol boats . Austria @-@ Hungary declared war on Serbia on 28 July 1914 , and that night the flotilla fired the first shots of the war against fortifications at the Zemun – Belgrade railway bridge over the river Sava and on the Topčider Hill , although Körös was not initially involved . The Serbs were outgunned by the monitors , and by August began to receive assistance from the Russians . This support included the supply and emplacement of naval guns and the establishment of river obstacles and mines . 
