The first shots of World War I were fired by the Austro-Hungarian river monitor Bodrog on Serbian defences near Belgrade.

River monitors are military craft designed to patrol rivers. They are normally the largest of all riverine warships in river flotillas, and mount the heaviest weapons. The name originated from the US Navy's USS Monitor, which made her first appearance in the American Civil War, and being distinguished by the use of revolving gun turrets, which were particularly useful in rivers, whose narrow channels could severely limit the directions vessels could face.

The Yugoslav monitor Sava is a Temes-class river monitor that was built for the Austro-Hungarian Navy as SMS Bodrog. She fired the first shots of World War I just after 01:00 on 29 July 1914, when she and two other monitors shelled Serbian defences near Belgrade. She was part of the Danube Flotilla, and fought the Serbian and Romanian armies from Belgrade to the mouth of the Danube. In the closing stages of the war, she was the last monitor to withdraw towards Budapest, but was captured by the Serbs when she grounded on a sandbank downstream from Belgrade. After the war, she was transferred to the newly created Kingdom of Serbs, Croats and Slovenes, and renamed Sava. She remained in service throughout the interwar period, although budget restrictions meant she was not always in full commission.

Belgrade is the capital and largest city of Serbia. It is located at the confluence of the Sava and Danube rivers and at the crossroads of the Pannonian Plain and the Balkan Peninsula. According to the 2022 census, the population of Belgrade city proper stands at 1,197,114, its contiguous urban area has 1,298,661 inhabitants, while population of city's administrative area totals 1,681,405 people. It is one of the major cities of Southeast Europe and the third-most populous city on the river Danube.