 On that day , Sava and her fellow monitor Vardar fought off several attacks by individual Luftwaffe aircraft on their base . Over the next three days , the two monitors laid mines in the Danube near the Romanian border . On 11 April , they were forced to withdraw from Dubovac towards Belgrade . During their withdrawal , they came under repeated attacks by Junkers Ju 87 Stuka dive bombers . Sava and her fellow monitor were undamaged , and anchored at the confluence of the Danube and Sava near Belgrade at about 20 : 00 , where they were joined by the 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 then 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 . 
