The B-class submarines were initially assigned to the Third Division of the Home Fleet, based at Portsmouth and Devonport, and were tasked with coastal-defence duties and defending the Straits of Dover in wartime.

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.

[5] 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.

During the boat's 6–10 June patrol in conjunction with the Italian submarine Pullino, B10 made an unsuccessful attack on the small steamship SS Arsa that was towing two barges.

[6] After returning from patrol on 9 August, she moored next to the Italian armoured cruiser Marco Polo which was serving as a depot ship for the British submarines and other small craft.

Later that night 21 aircraft from the Austro-Hungarian Naval Air Service (Kaiserliche und Königliche Seeflugwesen) attacked the military installations around Venice.

A workman drilled into the tank on 31 August and ignited a fire that could only extinguished by flooding the dry dock, which ruined all of the work already done.