[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.

[1] On the surface, the B class had a range of 1,000 nautical miles (1,900 km; 1,200 mi) at 8.7 knots (16.1 km/h; 10.0 mph).

They could carry a pair of reload torpedoes, but generally did not as they would have to remove an equal weight of fuel in compensation.

The boat was lost when she accidentally collided with SS Amerika 4 mi (6.4 km) northeast of Dover in the early hours of 4 October 1912.

O’Brien and was one of several submarines sent to Dover to take part in Channel exercises during the extended lead up to the First World War.