HMS B1 was the lead boat of the B-class submarines built for the Royal Navy in the first decade of the 20th century.

[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 built at the Vickers shipyard in Barrow-in-Furness and launched on 25 October 1904.