Yugoslav monitor Vardar

Temes (II) was commissioned into the Danube Flotilla in 1915, and was in action against the Serbian Army at Belgrade in early October, when the Serbs evacuated the city in the face of an Austro-Hungarian assault. During the final river crossing and reinforcement of the resulting bridgehead, Temes (II) provided close support. During this task, she attempted to draw fire away from the battle-damaged monitor Enns but after receiving a direct hit in the crew quarters aft, she had to move out of range. She was run ashore to put out fires and stop leaks, before being towed out of the battle area by an armed steamer, and taken to Budapest for repairs.[7]

In November 1915, the other monitors were assembled at Rustschuk, Bulgaria.[8] The geopolitical position of Romania was uncertain, with the Central Powers being aware that the Romanians were negotiating to enter the war on the side of the Entente. To protect the 480-kilometre (300 mi) Danubian border between Romania and Bulgaria, the flotilla established a sheltered base in the Belene Canal.[9] When the Romanians entered the war on 27 August 1916, the monitors were again at Rustschuk, having been joined by Temes (II) after her repairs were completed. The monitors were immediately attacked by three improvised torpedo boats operating out of the Romanian river port of Giurgiu. The torpedoes that were fired missed the monitors, but struck a lighter loaded with fuel. The 1st Monitor Division, including Temes (II), was tasked with escorting supply ships back to the Belene anchorage. This was followed by forays of the Division both east and west of Belene, during which both Turnu Măgurele and Zimnicea were shelled.[10] On 9 May 1917, she was renamed SMS Bosna as the original SMS Temes was due to return to service after a complete rebuild.[1]

In April 1918, Bosna—along with three other monitors, two patrol boats and a tug—were formed into Flottenabteilung Wulff (Fleet Division Wulff) under the command of Flottenkapitän (Fleet Captain) Olav Wulff. Flottenabteilung Wulff was sent through the mouth of the Danube and across the Black Sea to Odessa, where it spent several months supporting the Austro-Hungarian troops enforcing the peace agreement with Russia. It returned to the Danube at the end of August, and was anchored at Brăila on 12 September. On 16 October, Bosna and the rest of the 1st Monitor Division sailed from Brăila to Belene. The Danube Flotilla then protected Austro-Hungarian troops withdrawing towards Budapest, fighting French and irregular Serbian forces as they withdrew, and arrived on 6 November.[11]

After the Armistice of Villa Giusti signed by the Austro-Hungarians on 3 November 1918, Bosna was operated by the navy of the Hungarian People's Republic between 6 November and 13 December.[12] She was then crewed by sailors of the newly created Kingdom of Serbs, Croats and Slovenes (KSCS, later the Kingdom of Yugoslavia) in 1918–19. Under the terms of the Treaty of Saint-Germain-en-Laye concluded in September 1919, Bosna was transferred to the KSCS along with a range of other vessels, including three other river monitors,[13] but was officially handed over to the KSCS Navy and renamed Vardar in 1920.[14] In 1925–26, Vardar was refitted, but by the following year only two of the four river monitors of the KSCS Navy were being retained in full commission at any time.[15] In 1932, the British naval attaché reported that Yugoslav ships were engaging in little gunnery training, and few exercises or manoeuvres, due to reduced budgets.[16]

On 6 April 1941, the German-led Axis invasion of Yugoslavia began, and Vardar was based at Dubovac, as the flagship of the 1st Monitor Division,[17] responsible for the Romanian border on the Danube, under the operational control of the 3rd Infantry Division Dunavska.[18] She was commanded by Poručnik bojnog broda[lower-alpha 2] Milivoj Kockar.[17] On that day, Vardar and her fellow monitor Sava fought off several attacks by individual Luftwaffe aircraft on their base.[20] Over the next three days, the two monitors laid mines in the Danube near the Romanian border.[21]

On 11 April, the two monitors were forced to withdraw from Dubovac towards Belgrade,[22] during which they came under repeated attacks by Junkers Ju 87 Stuka dive bombers.[23] Vardar and her fellow monitor were undamaged, and anchored at the confluence of the Danube and Sava near Belgrade about 20:00, where they were joined by the monitor Morava. The three captains conferred, and decided to scuttle their vessels due to the high water levels in the rivers and low bridges, which meant there was insufficient clearance for the monitors to navigate freely. The crews of the monitors were transshipped to two tugboats, but when one of the tugboats was passing under a railway bridge, charges on the bridge accidentally exploded and the bridge fell onto the tugboat. Of the 110 officers and men aboard the vessel, 95 were killed.[22][24]

After the scuttling of the monitors, around 450 officers and men from the Vardar and various other riverine vessels gathered at Obrenovac. Armed only with personal weapons and some machine guns stripped from the scuttled vessels, they started towards the Bay of Kotor in the southern Adriatic in two groups. The smaller of the two groups reached its objective,[25] but the larger group only made it as far as Sarajevo by 14 April when they surrendered to German troops approaching the city.[26] The Bay of Kotor was captured by the Italian XVII Corps on 17 April.[27]