HMS B6 was one of 11 B-class submarines built for the Royal Navy in the first decade of the 20th century. The boat survived the First World War and was sold for scrap in 1921.
The B class was an enlarged and improved version of the preceding A class. The submarine had a length of 142 feet 3 inches (43.4 m) overall, a beam of 12 feet 7 inches (3.8 m) and a mean draft of 11 feet 2 inches (3.4 m). They displaced 287 long tons (292 t) on the surface and 316 long tons (321 t) submerged. The B-class submarines had a crew of two officers and thirteen ratings.
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. When submerged the propeller was driven by a 180-horsepower (134 kW) electric motor. They could reach 12 knots (22 km/h; 14 mph) on the surface and 6.5 knots (12.0 km/h; 7.5 mph) underwater. 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).