[1] For surface running, the boats were powered by a single 16-cylinder 600-brake-horsepower (447 kW) Vickers petrol engine that drove one propeller shaft.

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 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 five British submarines made a total of 13 patrols off the Austro-Hungarian coast before the end of 1915, hampered by bad weather and drifting mines, followed by 13 more in the first two months of 1916.

Redesignated as S9 in August 1917, the boat was assigned to patrol the Otranto Barrage that was intended to prevent the Austro-Hungarian Navy from breaking out of the Adriatic, although she proved to be very unreliable in service.