After the start of the First World War and the unsuccessful pursuit of the German ships "Goeben" and "Breslau" in August 1914, the B-class submarines were transferred to the Dardanelles area in mid-September to prevent any breakout attempt by the German ships. After the arrival of the larger and more modern E-class submarines in early 1915, the B-class boats began to return to Malta. After the Kingdom of Italy joined the Allies in May 1915, the B-class submarines in the Mediterranean were transferred to Venice to reinforce Italian forces in the northern Adriatic. The first boats began arriving there in October, but "B10" was still being refitted and did not join them until 20 March 1916, although she had made one patrol from Brindisi, Italy, that had to be terminated early with mechanical problems. After her arrival, the boat made uneventful patrols in the Kvarner Gulf on 9–11 and 26–28 April, and followed them up with three more patrols in May during which "B10" saw no targets. During the boat's 6–10 June patrol in conjunction with the , "B10" made an unsuccessful attack on the small steamship that was towing two barges. During her next patrol on 2–4 July, the boat snagged the mooring wire on a naval mine, but was able to sever it before it could hit the submarine. Later that month, "B10" was harassed by seven Austro-Hungarian torpedo boats on the 19th.