 In November 1915 , Bodrog and the other monitors were assembled at Rustschuk , Bulgaria . The Central Powers were aware that the Romanians were negotiating to enter the war on the side of the Entente , so the flotilla established a sheltered base in the Belene Canal to protect the 480 @-@ kilometre ( 300 mi ) Danube border between Romania and Bulgaria . During 1915 , the 37 mm ( 1 @.@ 5 in ) guns on the Bodrog were replaced with a single 66 mm ( 2 @.@ 6 in ) L / 18 gun , and three machine guns were also fitted . 
