[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.

On 4 June she was patrolling off Pola with only her conning tower above water when she was attacked by two Austro-Hungarian Lohner L flying boats.

Redesignated as S7 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.